1 00:00:00,000 --> 00:00:02,425 [SQUEAKING][RUSTLING][CLICKING] 2 00:00:15,543 --> 00:00:17,710 JEFFREY GROSSMAN: All right, how are you guys doing? 3 00:00:17,710 --> 00:00:18,640 [CHEERING] 4 00:00:18,640 --> 00:00:19,690 Thank you. 5 00:00:19,690 --> 00:00:20,290 You know why? 6 00:00:20,290 --> 00:00:23,110 This is such an amazing day. 7 00:00:23,110 --> 00:00:26,840 All right, first of all, we're going to talk about phases. 8 00:00:26,840 --> 00:00:33,400 And there are two lectures that I have introduced 9 00:00:33,400 --> 00:00:37,240 this semester that are new, that have never been seen before, 10 00:00:37,240 --> 00:00:38,960 until right now. 11 00:00:38,960 --> 00:00:41,070 One of them is this one. 12 00:00:41,070 --> 00:00:42,730 Right, Dane, thank you. 13 00:00:42,730 --> 00:00:46,300 And then, check this out, this morning over the wires 14 00:00:46,300 --> 00:00:47,850 comes this news. 15 00:00:47,850 --> 00:00:50,950 And it's the Nobel Prize in chemistry 16 00:00:50,950 --> 00:00:55,300 this year was given to 3 of sort of the founders of lithium ion 17 00:00:55,300 --> 00:00:56,440 batteries. 18 00:00:56,440 --> 00:00:58,180 And the other new lecture that I'm 19 00:00:58,180 --> 00:01:00,160 giving this semester, later on, is 20 00:01:00,160 --> 00:01:02,020 on the chemistry of batteries. 21 00:01:02,020 --> 00:01:03,820 It's like coincidence? 22 00:01:03,820 --> 00:01:05,200 [LAUGHTER] 23 00:01:05,200 --> 00:01:06,700 I don't think so. 24 00:01:06,700 --> 00:01:09,850 Did someone in Stockholm know? 25 00:01:09,850 --> 00:01:10,870 I don't know. 26 00:01:10,870 --> 00:01:13,130 But it's really, really cool. 27 00:01:13,130 --> 00:01:14,050 And this is awesome. 28 00:01:14,050 --> 00:01:15,820 And there's so much great stuff online now 29 00:01:15,820 --> 00:01:17,850 about lithium ion batteries, because of this. 30 00:01:17,850 --> 00:01:20,350 I mean there was before, but there is a lot of press on this 31 00:01:20,350 --> 00:01:20,850 now. 32 00:01:20,850 --> 00:01:22,870 It's very interesting to read about. 33 00:01:22,870 --> 00:01:23,740 OK. 34 00:01:23,740 --> 00:01:27,790 So now, what is happening? 35 00:01:27,790 --> 00:01:30,350 I say the word boiling all the time. 36 00:01:30,350 --> 00:01:30,850 Right. 37 00:01:30,850 --> 00:01:34,650 I've been saying it all the time, especially the last week. 38 00:01:34,650 --> 00:01:37,930 And I mean at home, too, I'm saying boiling a lot. 39 00:01:37,930 --> 00:01:40,542 And it's because it's a proxy for bond strength, 40 00:01:40,542 --> 00:01:42,250 intramolecular bond strength and boiling, 41 00:01:42,250 --> 00:01:43,450 I've been kind of going back and forth. 42 00:01:43,450 --> 00:01:43,920 Right. 43 00:01:43,920 --> 00:01:45,503 But so, today, we're going to go, what 44 00:01:45,503 --> 00:01:47,410 is happening when you boil? 45 00:01:47,410 --> 00:01:48,040 All right. 46 00:01:48,040 --> 00:01:50,410 Well, you know that you're changing a phase, 47 00:01:50,410 --> 00:01:54,735 as you can see from this highly accurate drawing of water 48 00:01:54,735 --> 00:01:56,110 molecules in the gas phase, water 49 00:01:56,110 --> 00:01:58,210 molecules in the liquid phase. 50 00:01:58,210 --> 00:02:00,160 But what's really under the hood? 51 00:02:00,160 --> 00:02:03,650 And of course, the story starts with Otto. 52 00:02:03,650 --> 00:02:06,520 Now who was Otto? 53 00:02:06,520 --> 00:02:08,590 Otto Von Guericke. 54 00:02:08,590 --> 00:02:11,980 Otto Von Guericke in the 1600s. 55 00:02:11,980 --> 00:02:13,270 He was like-- you know what-- 56 00:02:13,270 --> 00:02:14,860 Aristotle. 57 00:02:14,860 --> 00:02:19,440 Aristotle, he was all about like nature abhors a vacuum. 58 00:02:19,440 --> 00:02:20,500 Does it really? 59 00:02:20,500 --> 00:02:21,310 I don't know. 60 00:02:21,310 --> 00:02:25,000 I don't-- you know, does nature really hate? 61 00:02:25,000 --> 00:02:27,100 Like, let's try some stuff out. 62 00:02:27,100 --> 00:02:30,140 Let's try to make a vacuum, and see what happens. 63 00:02:30,140 --> 00:02:32,470 So he figured out a way to take these two 64 00:02:32,470 --> 00:02:34,540 hemispheres, these two big bowls, 65 00:02:34,540 --> 00:02:36,140 and kind of pull all the air out. 66 00:02:36,140 --> 00:02:36,640 There he is. 67 00:02:36,640 --> 00:02:38,100 He looks very happy there. 68 00:02:38,100 --> 00:02:39,360 Right. 69 00:02:39,360 --> 00:02:42,430 And he's pulling-- because he's pumping the air out inside 70 00:02:42,430 --> 00:02:44,240 of here, and look he did. 71 00:02:44,240 --> 00:02:46,050 He went around the countryside in Germany, 72 00:02:46,050 --> 00:02:48,850 and he would attach-- gesundheit-- just attach eight 73 00:02:48,850 --> 00:02:51,160 horses to one side, and eight horses to another, 74 00:02:51,160 --> 00:02:53,633 16 horses pulling. 75 00:02:53,633 --> 00:02:55,300 Eight that way, eight that way, and they 76 00:02:55,300 --> 00:02:57,590 couldn't pull it apart. 77 00:02:57,590 --> 00:02:58,990 This is what he did. 78 00:02:58,990 --> 00:03:01,330 It doesn't look like he's got a lot of crowd, 79 00:03:01,330 --> 00:03:02,980 but maybe he did better. 80 00:03:02,980 --> 00:03:04,320 I don't see any houses either. 81 00:03:04,320 --> 00:03:05,650 I don't know where he is. 82 00:03:05,650 --> 00:03:08,650 But that's the experiment that he did all 83 00:03:08,650 --> 00:03:10,780 throughout the countryside. 84 00:03:10,780 --> 00:03:14,560 And he called it the power of the vacuum. 85 00:03:14,560 --> 00:03:18,620 Nature abhors a vacuum, the power of the vacuum. 86 00:03:18,620 --> 00:03:19,470 Power of the vacuum. 87 00:03:19,470 --> 00:03:21,160 It's not the power of the vacuum. 88 00:03:21,160 --> 00:03:25,180 Oh, Otto, it's not the power of the vacuum, 89 00:03:25,180 --> 00:03:28,480 because vacuum has no power, and nature doesn't hate it. 90 00:03:31,120 --> 00:03:36,590 But pressure-- so atmosphere has power. 91 00:03:36,590 --> 00:03:38,540 Technically, it has force. 92 00:03:38,540 --> 00:03:39,680 Atmosphere has pressure. 93 00:03:39,680 --> 00:03:42,430 What he showed in that experiment, 94 00:03:42,430 --> 00:03:44,090 and if there's one experiment I want 95 00:03:44,090 --> 00:03:47,713 you to remember from this class, it's not this one. 96 00:03:47,713 --> 00:03:48,680 [LAUGHTER] 97 00:03:48,680 --> 00:03:51,410 But this is a cool one. 98 00:03:51,410 --> 00:03:53,480 But what he showed wasn't the power vacuum, 99 00:03:53,480 --> 00:03:57,840 he showed the power of one atmosphere of pressure. 100 00:03:57,840 --> 00:04:00,240 He showed the power of pressure. 101 00:04:00,240 --> 00:04:01,460 And so we start. 102 00:04:01,460 --> 00:04:05,120 Pressure is force over area. 103 00:04:05,120 --> 00:04:09,620 Typical units would be like newtons per meter squared, 104 00:04:09,620 --> 00:04:11,690 right. 105 00:04:11,690 --> 00:04:13,890 And if you're going newtons per meter squared, 106 00:04:13,890 --> 00:04:15,860 then this is called the pascal. 107 00:04:15,860 --> 00:04:22,670 And for reference, if you have one pascal, one pascal, 108 00:04:22,670 --> 00:04:30,260 it's about the pressure of a dollar bill, $1 resting 109 00:04:30,260 --> 00:04:31,338 on a table. 110 00:04:31,338 --> 00:04:31,880 I don't know. 111 00:04:31,880 --> 00:04:33,020 Why do I use that one? 112 00:04:33,020 --> 00:04:37,400 Because I remember it, $1 resting on a table. 113 00:04:37,400 --> 00:04:41,040 And so that's the force per area of the bill resting on a table. 114 00:04:41,040 --> 00:04:45,080 So if you had 100,000 of them, right, 115 00:04:45,080 --> 00:04:47,820 if you had 100,000 of them, and you stacked them up, 116 00:04:47,820 --> 00:04:50,960 then that's one atmosphere. 117 00:04:50,960 --> 00:04:52,420 That's just a different unit. 118 00:04:52,420 --> 00:04:55,140 It's about 100,000 pascals. 119 00:04:55,140 --> 00:05:01,540 So the power that he was exhibiting in this experiment 120 00:05:01,540 --> 00:05:04,830 is the power of the atmosphere. 121 00:05:04,830 --> 00:05:12,020 We've got-- we've got atmosphere all around us, pushing on us. 122 00:05:12,020 --> 00:05:13,080 It's pushing on us. 123 00:05:13,080 --> 00:05:17,000 And so, we got like a car worth of atmosphere, 124 00:05:17,000 --> 00:05:19,073 literally, on us, but it's pushing on us 125 00:05:19,073 --> 00:05:20,240 in all different directions. 126 00:05:20,240 --> 00:05:21,860 And we're pushing back. 127 00:05:21,860 --> 00:05:25,820 Luckily, we've got stuff inside of us, 128 00:05:25,820 --> 00:05:27,980 so we don't like implode. 129 00:05:27,980 --> 00:05:29,460 Right. 130 00:05:29,460 --> 00:05:33,290 That force is strong, and that's a demonstration of how strong, 131 00:05:33,290 --> 00:05:36,790 how much one atmosphere is. 132 00:05:36,790 --> 00:05:37,760 Right. 133 00:05:37,760 --> 00:05:40,910 It's force per area, the power of one atmosphere. 134 00:05:40,910 --> 00:05:43,160 Well, that's also directly related to boiling. 135 00:05:43,160 --> 00:05:45,140 And how do we get from here to boiling? 136 00:05:45,140 --> 00:05:48,110 Well, so we need a couple of concepts, right. 137 00:05:48,110 --> 00:05:53,180 So first, we need the concept of evaporation. 138 00:05:53,180 --> 00:05:55,320 And I'm going to use this-- 139 00:05:55,320 --> 00:05:57,950 I'm going to use this example of like water molecules, right. 140 00:05:57,950 --> 00:05:58,910 So this is a-- 141 00:05:58,910 --> 00:06:01,010 this is a glass of water. 142 00:06:01,010 --> 00:06:01,610 Right. 143 00:06:01,610 --> 00:06:04,418 And so, if I have a glass of water, 144 00:06:04,418 --> 00:06:06,710 I'm going to draw them like these little things-- yeah, 145 00:06:06,710 --> 00:06:08,930 and now molecules kind of near the surface-- 146 00:06:08,930 --> 00:06:10,860 well, it could leave. 147 00:06:10,860 --> 00:06:15,080 And that is-- that's a molecule, not a v, right, and that's 148 00:06:15,080 --> 00:06:17,930 evaporation, evaporation. 149 00:06:17,930 --> 00:06:20,120 Evaporation. 150 00:06:20,120 --> 00:06:21,980 But, you know, the other way you could go 151 00:06:21,980 --> 00:06:24,740 is, you could say, well, what if there was this liquid here, 152 00:06:24,740 --> 00:06:27,380 and you've got these molecules, kind of like that. 153 00:06:27,380 --> 00:06:28,880 And you had one here. 154 00:06:28,880 --> 00:06:30,320 And it kind of comes back. 155 00:06:30,320 --> 00:06:31,850 Well, that's condensation. 156 00:06:31,850 --> 00:06:33,440 You guys kind of know this, right? 157 00:06:33,440 --> 00:06:34,390 Condensation. 158 00:06:37,490 --> 00:06:39,350 Evaporation and condensation. 159 00:06:39,350 --> 00:06:41,660 Oh, but this is not what's interesting. 160 00:06:41,660 --> 00:06:43,790 I mean it's interesting, but it's-- but it's more 161 00:06:43,790 --> 00:06:46,120 interesting now if you close it off. 162 00:06:46,120 --> 00:06:50,460 And so, let's do that with these super amazing animations 163 00:06:50,460 --> 00:06:52,250 here-- they're there. 164 00:06:52,250 --> 00:06:52,920 Look at that. 165 00:06:52,920 --> 00:06:53,150 OK. 166 00:06:53,150 --> 00:06:55,160 So now what I've done, I've got a liquid and a solid. 167 00:06:55,160 --> 00:06:56,780 And in both cases, there's a liquid. 168 00:06:56,780 --> 00:06:57,830 You could have solid. 169 00:06:57,830 --> 00:06:59,330 Molecules can come off. 170 00:06:59,330 --> 00:07:00,160 We'll get to that. 171 00:07:00,160 --> 00:07:00,660 How? 172 00:07:00,660 --> 00:07:01,820 Why? 173 00:07:01,820 --> 00:07:03,630 They can come off. 174 00:07:03,630 --> 00:07:04,980 But now I've closed it. 175 00:07:04,980 --> 00:07:08,180 Now if I close the container, what 176 00:07:08,180 --> 00:07:10,250 would happen if I start with nothing? 177 00:07:10,250 --> 00:07:13,057 So now I start with a liquid, and I close it in a container. 178 00:07:13,057 --> 00:07:14,390 You see-- look at the molecules. 179 00:07:14,390 --> 00:07:15,618 They're kind of coming off. 180 00:07:15,618 --> 00:07:17,660 And maybe they'll hit the walls or bounce around, 181 00:07:17,660 --> 00:07:22,142 maybe at some point, they'll come back into the liquid. 182 00:07:22,142 --> 00:07:23,050 Right. 183 00:07:23,050 --> 00:07:24,130 OK. 184 00:07:24,130 --> 00:07:26,770 So evaporation went that way. 185 00:07:26,770 --> 00:07:28,580 Condensation went that way. 186 00:07:28,580 --> 00:07:33,280 Now-- ah-- now, if I were to plot, 187 00:07:33,280 --> 00:07:39,010 if I were to close this and plot, for example, a rate. 188 00:07:39,010 --> 00:07:42,370 And I say, well, I want to know how quickly evaporation 189 00:07:42,370 --> 00:07:44,803 is happening. 190 00:07:44,803 --> 00:07:46,220 It's just going to keep happening. 191 00:07:46,220 --> 00:07:49,850 I mean I'm starting with, you see in the videos-- 192 00:07:49,850 --> 00:07:53,210 these videos are real-- 193 00:07:53,210 --> 00:07:55,620 you see it doesn't stop happening. 194 00:07:55,620 --> 00:07:56,120 right. 195 00:07:56,120 --> 00:07:56,912 It keeps happening. 196 00:07:56,912 --> 00:07:59,810 So if I have no vapor in there to begin with, well, then, 197 00:07:59,810 --> 00:08:02,920 OK, evaporation is going to go like this. 198 00:08:02,920 --> 00:08:06,740 All right, maybe this is time, it is time. 199 00:08:06,740 --> 00:08:09,760 And then-- so that's evaporation. 200 00:08:09,760 --> 00:08:11,760 But then, at a certain time, at a certain point, 201 00:08:11,760 --> 00:08:14,480 I'm going to have enough gas molecules, gas water 202 00:08:14,480 --> 00:08:15,710 molecules in there. 203 00:08:15,710 --> 00:08:18,325 So it starts out at 0, and they're 204 00:08:18,325 --> 00:08:20,450 going to build up in there, and at a certain point, 205 00:08:20,450 --> 00:08:21,240 you got that. 206 00:08:21,240 --> 00:08:21,740 Right. 207 00:08:21,740 --> 00:08:24,060 And so, this would be condensation. 208 00:08:24,060 --> 00:08:24,560 OK. 209 00:08:24,560 --> 00:08:27,630 We're starting with the basics, condensation. 210 00:08:27,630 --> 00:08:28,970 Right. 211 00:08:28,970 --> 00:08:32,270 And then at a certain point, they 212 00:08:32,270 --> 00:08:37,985 reach what's called dynamic equilibrium, dynamic eqm, 213 00:08:37,985 --> 00:08:39,260 eqm is equilibrium. 214 00:08:41,780 --> 00:08:44,660 So the dynamic equilibrium is really important, 215 00:08:44,660 --> 00:08:48,590 because what happens there is nothing is stopping. 216 00:08:48,590 --> 00:08:49,820 It's not the thing stopped. 217 00:08:49,820 --> 00:08:52,220 You can see it in the videos. 218 00:08:52,220 --> 00:08:55,570 I found it online, so it must be right. 219 00:08:55,570 --> 00:08:58,100 So like, you know, it's continually going. 220 00:08:58,100 --> 00:08:59,510 It's a dynamic process. 221 00:08:59,510 --> 00:09:02,090 It's a dynamic equilibrium, but they are equal. 222 00:09:02,090 --> 00:09:06,110 That point that happens in these containers, 223 00:09:06,110 --> 00:09:08,460 you can measure the pressure. 224 00:09:08,460 --> 00:09:10,240 That is very important. 225 00:09:10,240 --> 00:09:11,340 Right. 226 00:09:11,340 --> 00:09:13,680 Because it's exerting a pressure on the container. 227 00:09:13,680 --> 00:09:16,140 It's exerting a pressure on the liquid. 228 00:09:16,140 --> 00:09:17,220 Pressure. 229 00:09:17,220 --> 00:09:18,150 Atmosphere. 230 00:09:18,150 --> 00:09:22,210 Pressure, inside of a closed container, vapor pressure. 231 00:09:22,210 --> 00:09:23,130 P vapor. 232 00:09:27,330 --> 00:09:30,383 That happens when you hit that dynamic equilibrium. 233 00:09:30,383 --> 00:09:31,800 Now why am I telling you all this? 234 00:09:31,800 --> 00:09:33,180 Well, the vapor pressure is going 235 00:09:33,180 --> 00:09:36,680 to be how we understand phase change. 236 00:09:36,680 --> 00:09:39,300 And so-- and so-- 237 00:09:39,300 --> 00:09:43,590 you kind of get a sense already, kind of get a sense already, 238 00:09:43,590 --> 00:09:46,950 that this is going to be related-- 239 00:09:46,950 --> 00:09:53,860 this is related, you know, this depends on the bonding. 240 00:09:53,860 --> 00:09:54,360 Right. 241 00:09:54,360 --> 00:09:58,910 So I just told you that water was really special. 242 00:09:58,910 --> 00:10:00,640 So that means that how it-- 243 00:10:00,640 --> 00:10:02,500 it's the bonding between the water molecules 244 00:10:02,500 --> 00:10:05,860 and how often can it get out of the liquid, 245 00:10:05,860 --> 00:10:08,587 it's related to the bonding. 246 00:10:08,587 --> 00:10:11,210 Right. 247 00:10:11,210 --> 00:10:14,670 So if you take molecules that we talked about on Monday-- 248 00:10:14,670 --> 00:10:18,020 these are just from Monday-- propane and butane, 249 00:10:18,020 --> 00:10:20,600 now you understand, right? 250 00:10:20,600 --> 00:10:23,960 Why is there this difference in the vapor pressure of protane-- 251 00:10:23,960 --> 00:10:26,390 propane, and the vapor pressure of butane? 252 00:10:26,390 --> 00:10:27,830 Well, it's how they bond together. 253 00:10:27,830 --> 00:10:29,390 And you know exactly why. 254 00:10:29,390 --> 00:10:33,050 Because these are only able to do [INAUDIBLE].. 255 00:10:33,050 --> 00:10:34,160 And so, this has a-- 256 00:10:34,160 --> 00:10:35,810 has a higher surface area. 257 00:10:35,810 --> 00:10:38,030 We talk about this in terms of the boiling point, 258 00:10:38,030 --> 00:10:40,580 remember, as a proxy for the intermolecular bonding 259 00:10:40,580 --> 00:10:41,200 strength. 260 00:10:41,200 --> 00:10:43,732 And now I'm giving you the vapor pressure. 261 00:10:43,732 --> 00:10:46,190 So this is the vapor pressure of these things is different. 262 00:10:46,190 --> 00:10:49,250 Those are measured-- those are given a kilopascal. 263 00:10:49,250 --> 00:10:51,200 So if it's water-- 264 00:10:51,200 --> 00:10:53,473 so the water vapor pressure-- 265 00:10:53,473 --> 00:10:56,700 right-- let's see, make sure I get this value-- 266 00:10:56,700 --> 00:11:00,030 yes-- P-- 267 00:11:00,030 --> 00:11:08,010 I'll just put a Pv for water, is about 2.3 kilopascal. 268 00:11:08,010 --> 00:11:10,960 So it's a lot lower than those. 269 00:11:10,960 --> 00:11:11,460 Right. 270 00:11:11,460 --> 00:11:14,220 Those are-- now, in atmospheres, and this 271 00:11:14,220 --> 00:11:20,410 is going to be important, 0.02 atmospheres. 272 00:11:20,410 --> 00:11:22,740 Just switching around units, that's all. 273 00:11:22,740 --> 00:11:23,700 It's same thing. 274 00:11:23,700 --> 00:11:24,820 Gesundheit. 275 00:11:24,820 --> 00:11:25,350 Right. 276 00:11:25,350 --> 00:11:30,030 So now, if a liquid is- you can think about this as, 277 00:11:30,030 --> 00:11:31,650 well, this is a proxy already. 278 00:11:31,650 --> 00:11:33,210 I can understand this conceptually. 279 00:11:33,210 --> 00:11:33,810 Right. 280 00:11:33,810 --> 00:11:36,990 It's a proxy for the intermolecular bonding. 281 00:11:36,990 --> 00:11:41,410 If you take something like glycerol-- 282 00:11:41,410 --> 00:11:45,840 well, glycerol is-- let's draw glycerol just for fun. 283 00:11:45,840 --> 00:11:52,620 Carbon, carbon, Oh-- let's see, it's got another carbon, 284 00:11:52,620 --> 00:11:56,940 OH, it's got another OH, look at all that, OHs. 285 00:11:56,940 --> 00:11:59,280 It's got some hydrogens down here. 286 00:11:59,280 --> 00:12:01,530 It's got another hydrogen in there, 287 00:12:01,530 --> 00:12:05,130 and it's got two more hydrogens out here. 288 00:12:05,130 --> 00:12:09,485 No, I am not paying attention to VSEPR right now. 289 00:12:09,485 --> 00:12:10,860 I'm just getting it on the board. 290 00:12:10,860 --> 00:12:12,990 But look-- but look at that. 291 00:12:12,990 --> 00:12:17,040 Right away, you're like, oh, look at those hydrogen bond 292 00:12:17,040 --> 00:12:18,720 opportunities. 293 00:12:18,720 --> 00:12:19,350 Yeah. 294 00:12:19,350 --> 00:12:22,572 This could bond more strongly than water to itself, right. 295 00:12:22,572 --> 00:12:24,030 It's got all that hydrogen bonding. 296 00:12:24,030 --> 00:12:25,980 It's got even more than water. 297 00:12:25,980 --> 00:12:34,920 And so the vapor pressure of this is 0.01 pascal. 298 00:12:34,920 --> 00:12:36,990 So much lower. 299 00:12:36,990 --> 00:12:41,180 And as a general rule, we like to compare everything to water. 300 00:12:41,180 --> 00:12:45,690 So if something has a vapor pressure that is higher 301 00:12:45,690 --> 00:12:53,130 than water, so it's called volatile, Pv greater than Pv 302 00:12:53,130 --> 00:12:56,350 water, it is volatile. 303 00:12:56,350 --> 00:13:00,960 It's a volatile liquid, like butane and propane. 304 00:13:00,960 --> 00:13:07,110 If it's less than Pv water, then it's called-- 305 00:13:07,110 --> 00:13:11,810 here it comes-- all those chemists-- non-volatile. 306 00:13:11,810 --> 00:13:13,050 Look at that. 307 00:13:13,050 --> 00:13:16,920 Look at that beautiful naming originality. 308 00:13:16,920 --> 00:13:17,420 OK. 309 00:13:17,420 --> 00:13:18,870 But this is the thing, right, I've 310 00:13:18,870 --> 00:13:21,193 given you this concept of vapor pressure. 311 00:13:21,193 --> 00:13:22,610 I've talked about it a little bit. 312 00:13:22,610 --> 00:13:25,230 You can relate it to something you just learned on Monday. 313 00:13:25,230 --> 00:13:30,060 But I still have not come back to boiling. 314 00:13:30,060 --> 00:13:31,320 And that really is it. 315 00:13:31,320 --> 00:13:37,890 It's that boiling is actually understood by vapor pressure. 316 00:13:37,890 --> 00:13:40,380 That is how we understand boiling. 317 00:13:40,380 --> 00:13:42,200 And so you can think about it-- let's just 318 00:13:42,200 --> 00:13:42,990 give it to you conceptually. 319 00:13:42,990 --> 00:13:43,490 Right. 320 00:13:43,490 --> 00:13:46,260 So if you had-- 321 00:13:46,260 --> 00:13:48,012 let's go back to those buckets there. 322 00:13:48,012 --> 00:13:49,470 Think of it-- we'll go back to like 323 00:13:49,470 --> 00:13:50,730 evaporation and condensation. 324 00:13:50,730 --> 00:13:53,310 But now, instead of being in a closed container, 325 00:13:53,310 --> 00:13:56,380 right, now I'm outside. 326 00:13:56,380 --> 00:14:00,420 So if I had, let's say I had this container here. 327 00:14:00,420 --> 00:14:02,850 And I've got all these waters in it. 328 00:14:02,850 --> 00:14:04,830 Right. 329 00:14:04,830 --> 00:14:06,150 But now I'm outside. 330 00:14:06,150 --> 00:14:10,020 So I've got the power of one atmosphere, right. 331 00:14:10,020 --> 00:14:13,430 One atmosphere. 332 00:14:13,430 --> 00:14:16,100 Well, you know, now you see, like, OK, 333 00:14:16,100 --> 00:14:19,520 if a molecule is able to evaporate from the liquid, 334 00:14:19,520 --> 00:14:22,490 if a molecule is able to leave the liquid bonding 335 00:14:22,490 --> 00:14:25,370 environment, breaking the bond, that's 336 00:14:25,370 --> 00:14:28,760 why we can relate it to intermolecular forces, right. 337 00:14:28,760 --> 00:14:30,770 It's breaking those bonds in the liquid, 338 00:14:30,770 --> 00:14:32,360 and becoming a gas phase molecule. 339 00:14:32,360 --> 00:14:34,340 It's changing its phase. 340 00:14:34,340 --> 00:14:35,810 Well, you know, then the question 341 00:14:35,810 --> 00:14:38,910 is, is it like going to-- what's it going to do? 342 00:14:38,910 --> 00:14:41,090 You know, is it going to kind of hang out here? 343 00:14:41,090 --> 00:14:43,400 And are the forces of the atmosphere, 344 00:14:43,400 --> 00:14:46,010 is the atmospheric pressure going to kind of hold it 345 00:14:46,010 --> 00:14:47,540 around there? 346 00:14:47,540 --> 00:14:52,340 Or, is it going to be able to leave? 347 00:14:52,340 --> 00:14:55,170 Well, this is a very simple conceptual picture. 348 00:14:55,170 --> 00:14:56,430 Right. 349 00:14:56,430 --> 00:14:58,430 If you thought that the forces of the atmosphere 350 00:14:58,430 --> 00:14:59,888 were going to always hold it there, 351 00:14:59,888 --> 00:15:02,860 then you'd say the atmosphere is a container. 352 00:15:02,860 --> 00:15:03,680 And it's not. 353 00:15:03,680 --> 00:15:05,510 But, actually, evaporation only happens 354 00:15:05,510 --> 00:15:08,940 because a breeze can come along and blow this away-- 355 00:15:08,940 --> 00:15:11,280 right-- out in the air. 356 00:15:11,280 --> 00:15:13,720 So those forces are super important, 357 00:15:13,720 --> 00:15:17,250 because as soon as the vapor pressure is greater 358 00:15:17,250 --> 00:15:19,530 than the atmospheric pressure, well, 359 00:15:19,530 --> 00:15:22,110 now you can get a sense of what-- the vapor pressure is 360 00:15:22,110 --> 00:15:26,100 greater than the pressure outside over that surface 361 00:15:26,100 --> 00:15:28,890 of the air here, then the molecule is just 362 00:15:28,890 --> 00:15:31,470 going to fly right out and power through it. 363 00:15:31,470 --> 00:15:33,015 That is the definition of boiling. 364 00:15:35,760 --> 00:15:38,340 Boiling is a pressure effect. 365 00:15:38,340 --> 00:15:42,720 It's that the vapor pressure of this material, which 366 00:15:42,720 --> 00:15:46,620 is related to how strongly it's bonded in the liquid compared 367 00:15:46,620 --> 00:15:50,070 to the gas phase, that that goes higher than the surrounding 368 00:15:50,070 --> 00:15:51,270 pressure. 369 00:15:51,270 --> 00:15:53,340 That's the definition of boiling. 370 00:15:56,560 --> 00:15:58,770 So you can see why water doesn't boil. 371 00:15:58,770 --> 00:16:00,740 Like having a bucket of water, and I watch it, 372 00:16:00,740 --> 00:16:01,820 it's not going to boil. 373 00:16:01,820 --> 00:16:05,160 0.02 atmospheres is not greater than one. 374 00:16:05,160 --> 00:16:07,730 Right. 375 00:16:07,730 --> 00:16:10,120 But so I haven't gotten there yet. 376 00:16:10,120 --> 00:16:11,760 I haven't made it boil. 377 00:16:11,760 --> 00:16:13,460 But I want to make a boil. 378 00:16:13,460 --> 00:16:16,980 And that is where we go next, because that is really 379 00:16:16,980 --> 00:16:18,450 what temperature is. 380 00:16:18,450 --> 00:16:21,870 See, the vapor pressure is really 381 00:16:21,870 --> 00:16:26,460 a link between temperature and boiling. 382 00:16:26,460 --> 00:16:29,580 It's the length that you need to understand between temperature 383 00:16:29,580 --> 00:16:30,930 and boiling. 384 00:16:30,930 --> 00:16:34,530 The reason why-- when you increase the temperature 385 00:16:34,530 --> 00:16:36,600 of the water, the reason why it boils 386 00:16:36,600 --> 00:16:40,020 is because you change its vapor pressure. 387 00:16:40,020 --> 00:16:41,550 That's why it boils. 388 00:16:41,550 --> 00:16:43,110 That's what boiling is. 389 00:16:43,110 --> 00:16:43,610 OK. 390 00:16:43,610 --> 00:16:47,550 It's when you get it above the atmospheric pressure. 391 00:16:47,550 --> 00:16:48,050 No. 392 00:16:51,400 --> 00:16:52,490 OK. 393 00:16:52,490 --> 00:16:55,090 So the-- so we got-- 394 00:16:55,090 --> 00:16:57,580 OK-- so are we-- where-- there we go-- 395 00:16:57,580 --> 00:17:00,230 we'll come to that in a minute. 396 00:17:00,230 --> 00:17:03,970 So if I were to plot now, the vapor pressure-- 397 00:17:03,970 --> 00:17:05,770 let's do this carefully here. 398 00:17:05,770 --> 00:17:06,760 OK. 399 00:17:06,760 --> 00:17:13,000 I'm going to make a plot of the vapor pressure, Pv, right, 400 00:17:13,000 --> 00:17:15,200 versus temperature. 401 00:17:15,200 --> 00:17:17,720 So I just told you there's a dependence on the temperature. 402 00:17:17,720 --> 00:17:18,220 Right. 403 00:17:18,220 --> 00:17:19,930 So versus temperature. 404 00:17:19,930 --> 00:17:23,619 Let's go to-- oh, I don't know-- let's go to room temperature. 405 00:17:23,619 --> 00:17:29,860 So around here, and I just told you that at 0.022 for 25 406 00:17:29,860 --> 00:17:32,950 C. OK, good. 407 00:17:32,950 --> 00:17:35,680 So 0.02 for 25. 408 00:17:35,680 --> 00:17:38,710 0.02 for 25 C. So that's the vapor pressure. 409 00:17:38,710 --> 00:17:40,820 That's the temperature. 410 00:17:40,820 --> 00:17:42,970 But I also told you that boiling-- 411 00:17:42,970 --> 00:17:47,980 if I'm at-- so this is 0-- but I also told you that boiling-- 412 00:17:47,980 --> 00:17:50,210 so this would be like one atmosphere. 413 00:17:50,210 --> 00:17:52,440 Let's suppose the units are atmospheres. 414 00:17:52,440 --> 00:17:53,960 Right. 415 00:17:53,960 --> 00:17:54,730 OK. 416 00:17:54,730 --> 00:17:56,562 So I told you that boiling happens-- 417 00:17:56,562 --> 00:17:59,020 now we know that water-- we know what the answer is, right, 418 00:17:59,020 --> 00:17:59,800 up here. 419 00:17:59,800 --> 00:18:04,900 That's got to be boiling for 100 C, right. 420 00:18:04,900 --> 00:18:08,133 That's where the water goes above 421 00:18:08,133 --> 00:18:09,550 or meets the atmospheric pressure, 422 00:18:09,550 --> 00:18:11,350 and then goes above it. 423 00:18:11,350 --> 00:18:13,105 So once the vapor pressure-- so if this 424 00:18:13,105 --> 00:18:16,720 is the vapor pressure of water, this is what we have so far. 425 00:18:16,720 --> 00:18:18,800 But we need more than that. 426 00:18:18,800 --> 00:18:21,550 So you can say, well, why is it-- 427 00:18:21,550 --> 00:18:23,120 so we know this-- 428 00:18:23,120 --> 00:18:26,660 why is it that if I go to Denver, the-- 429 00:18:26,660 --> 00:18:28,840 so like this is in Boston-- 430 00:18:28,840 --> 00:18:30,370 this is in Boston. 431 00:18:30,370 --> 00:18:32,350 This is Boston. 432 00:18:32,350 --> 00:18:33,890 But if I live in Denver-- 433 00:18:33,890 --> 00:18:36,460 how many people live in Denver-- 434 00:18:36,460 --> 00:18:38,710 well, I mean you're not living there now, but-- 435 00:18:38,710 --> 00:18:41,010 but, welcome to Boston. 436 00:18:41,010 --> 00:18:42,870 Oh, ho, ho. 437 00:18:42,870 --> 00:18:47,020 And if I go like this-- 438 00:18:47,020 --> 00:18:51,750 now see the thing is, now you boil at-- this 439 00:18:51,750 --> 00:18:55,060 is-- this is in Denver. 440 00:18:55,060 --> 00:18:59,190 So you guys don't have as much air in Denver. 441 00:18:59,190 --> 00:19:08,250 The pressure in Denver is 0.83, 0.83 atmospheres. 442 00:19:08,250 --> 00:19:10,290 But I just said that, you know, you 443 00:19:10,290 --> 00:19:12,390 boil when you have the vapor pressure is higher 444 00:19:12,390 --> 00:19:14,350 than the atmospheric pressure. 445 00:19:14,350 --> 00:19:16,122 So that means, whatever this curve 446 00:19:16,122 --> 00:19:17,580 is, it means that I'm going to boil 447 00:19:17,580 --> 00:19:19,050 at a different temperature. 448 00:19:19,050 --> 00:19:22,380 And it turns out that's 100, and if you're in Denver, 449 00:19:22,380 --> 00:19:25,590 it takes longer to boil potatoes, 450 00:19:25,590 --> 00:19:28,500 because the boiling temperature is 95. 451 00:19:28,500 --> 00:19:29,100 That's why. 452 00:19:29,100 --> 00:19:30,450 But it's all because of this. 453 00:19:30,450 --> 00:19:32,430 It's all because of how evaporation 454 00:19:32,430 --> 00:19:36,360 happens as it relates to the atmospheric pressure. 455 00:19:36,360 --> 00:19:38,700 Yeah, but-- the thing is, though, what we need-- 456 00:19:38,700 --> 00:19:41,300 and by the way, you know, you can go the other way, too. 457 00:19:41,300 --> 00:19:41,800 Right. 458 00:19:41,800 --> 00:19:43,200 You go up. 459 00:19:43,200 --> 00:19:46,550 If you go below sea level, then the atmospheric pressure 460 00:19:46,550 --> 00:19:47,050 is higher. 461 00:19:47,050 --> 00:19:52,080 So if you go to the Dead Sea, your water boils at 101.4. 462 00:19:52,080 --> 00:19:54,830 If you go to the top of Mount Everest, it's 70. 463 00:19:54,830 --> 00:19:56,760 You never boil potatoes there. 464 00:19:56,760 --> 00:19:59,970 Well, you can, but they'll never cook. 465 00:19:59,970 --> 00:20:00,870 So how do you-- 466 00:20:00,870 --> 00:20:02,610 how does this get connected? 467 00:20:02,610 --> 00:20:04,050 That's really the question. 468 00:20:04,050 --> 00:20:06,930 What is-- so what is this? 469 00:20:06,930 --> 00:20:07,440 Right. 470 00:20:07,440 --> 00:20:09,750 Where does that-- where does that dependence come from? 471 00:20:09,750 --> 00:20:11,280 And that's where we need something 472 00:20:11,280 --> 00:20:12,360 called kinetic theory. 473 00:20:12,360 --> 00:20:14,828 Now I'm not going to teach you kinetic theory. 474 00:20:14,828 --> 00:20:17,370 And I'm not going to say that you responsible for knowing it. 475 00:20:17,370 --> 00:20:20,045 But I'm showing you what it means. 476 00:20:20,045 --> 00:20:22,170 What kinetic theory does, which you would learn in, 477 00:20:22,170 --> 00:20:24,490 say like a thermal class, right. 478 00:20:24,490 --> 00:20:27,180 Well, kinetic theory does is it gives us 479 00:20:27,180 --> 00:20:30,660 this relationship between how many molecules have a given 480 00:20:30,660 --> 00:20:33,690 energy, in this case, it's a kinetic energy, right, 481 00:20:33,690 --> 00:20:35,340 and the temperature. 482 00:20:35,340 --> 00:20:37,200 That's what can in theory does for us. 483 00:20:37,200 --> 00:20:39,190 So let's see, if I had-- 484 00:20:43,550 --> 00:20:50,270 if I had to write this in a kind of just simple dependence way, 485 00:20:50,270 --> 00:20:53,665 what it's telling us, in, general is-- 486 00:20:53,665 --> 00:20:55,040 so this would be kinetic theory-- 487 00:20:57,900 --> 00:20:59,670 kinetic theory of gases, if you want. 488 00:20:59,670 --> 00:21:02,210 That's what we're talking about there. 489 00:21:02,210 --> 00:21:03,810 OK. 490 00:21:03,810 --> 00:21:05,550 This would give us the following. 491 00:21:05,550 --> 00:21:11,890 This is what you get is that the log of the fractions-- 492 00:21:14,940 --> 00:21:24,110 fraction of molecules with some energy, E, OK, with energy-- 493 00:21:24,110 --> 00:21:26,940 I'll write it out just so there's not confusion-- energy, 494 00:21:26,940 --> 00:21:30,900 E, the log of that, the natural log of that, 495 00:21:30,900 --> 00:21:34,710 is going to go as that energy divided by temperature. 496 00:21:34,710 --> 00:21:37,298 It gives you a connection between what 497 00:21:37,298 --> 00:21:38,340 I'm plotting here really. 498 00:21:38,340 --> 00:21:40,640 That's where that plot comes from. 499 00:21:40,640 --> 00:21:41,160 OK. 500 00:21:41,160 --> 00:21:43,890 The fraction of molecules with kinetic energy, 501 00:21:43,890 --> 00:21:49,150 E, goes as that energy divided by temperature. 502 00:21:49,150 --> 00:21:50,200 The log of that. 503 00:21:50,200 --> 00:21:51,850 That's what kinetic theory gives me. 504 00:21:51,850 --> 00:21:54,250 That fills it in, except that I-- 505 00:21:54,250 --> 00:21:56,480 it still isn't vapor pressure. 506 00:21:56,480 --> 00:21:56,980 Right. 507 00:21:56,980 --> 00:21:58,420 This still isn't vapor pressure. 508 00:21:58,420 --> 00:22:03,220 And so for that, you need one more piece. 509 00:22:03,220 --> 00:22:07,210 And that is given to us by Clausius-Clapeyron. 510 00:22:07,210 --> 00:22:12,312 So the Clausius-Clapeyron equation-- 511 00:22:12,312 --> 00:22:14,740 ah-- Clapeyron-- does not-- 512 00:22:14,740 --> 00:22:16,820 I'm not going to derive it. 513 00:22:16,820 --> 00:22:19,270 You don't need to know how to derive it. 514 00:22:19,270 --> 00:22:22,540 But it goes from the kinetic theory to vapor pressures. 515 00:22:22,540 --> 00:22:28,640 So this one tells us that the log of the vapor pressure 516 00:22:28,640 --> 00:22:30,140 equals minus-- 517 00:22:30,140 --> 00:22:34,430 and here we go-- this is the next really important concept-- 518 00:22:34,430 --> 00:22:36,765 the heat of vaporization-- 519 00:22:36,765 --> 00:22:38,510 and we'll get to this in a second-- 520 00:22:38,510 --> 00:22:42,060 divided by RT plus a constant. 521 00:22:42,060 --> 00:22:44,300 So that's the ideal gas constant. 522 00:22:44,300 --> 00:22:45,720 That's the temperature. 523 00:22:45,720 --> 00:22:50,040 And this is the enthalpy or the heat of vaporization. 524 00:22:50,040 --> 00:22:59,670 So it's the energy to vaporize a liquid. 525 00:22:59,670 --> 00:23:00,780 Good. 526 00:23:00,780 --> 00:23:04,180 Now, often, this is given in per mole. 527 00:23:04,180 --> 00:23:06,280 So it would be like the energy of vaporizing 528 00:23:06,280 --> 00:23:08,250 a mole of a liquid, but it's an energy. 529 00:23:08,250 --> 00:23:11,280 It's an amount of energy needed to turn it, 530 00:23:11,280 --> 00:23:13,110 whatever you got to put into it, to turn it 531 00:23:13,110 --> 00:23:15,630 into a gas from a liquid. 532 00:23:15,630 --> 00:23:17,190 That's that enthalpy of vaporization. 533 00:23:17,190 --> 00:23:19,290 And R is the ideal gas constant, in this case. 534 00:23:19,290 --> 00:23:22,140 You know, so if it's R-- 535 00:23:22,140 --> 00:23:25,470 if R is in the equation, it's got to be per mole, 536 00:23:25,470 --> 00:23:28,890 right, because it's R. Remember, we've 537 00:23:28,890 --> 00:23:30,090 already talked about that. 538 00:23:30,090 --> 00:23:31,900 Since it's R, it's the ideal gas constant. 539 00:23:31,900 --> 00:23:37,860 So that's, now, OK, so that is how you get between-- 540 00:23:37,860 --> 00:23:39,510 that is how you get this relationship. 541 00:23:39,510 --> 00:23:43,110 You get it, and, again, this is an important equation. 542 00:23:43,110 --> 00:23:45,750 You get it from the kinetic theory gases, 543 00:23:45,750 --> 00:23:47,970 but this is what the outcome is for us. 544 00:23:47,970 --> 00:23:52,000 This is what matters, is the Clausius-Clapeyron equation. 545 00:23:52,000 --> 00:23:55,230 And so, and so now, you can actually now, 546 00:23:55,230 --> 00:23:57,540 if somehow you knew how much energy it 547 00:23:57,540 --> 00:24:00,030 took to vaporize a mole of this stuff, 548 00:24:00,030 --> 00:24:02,130 well, now you've got a curve. 549 00:24:02,130 --> 00:24:05,070 That's all I need to know, right, is how much energy is-- 550 00:24:05,070 --> 00:24:08,250 so now, I can say, well, let's see, that's OK-- 551 00:24:08,250 --> 00:24:14,470 I got-- I got, maybe butane is going to go like this. 552 00:24:14,470 --> 00:24:18,120 And then glycerol might go like that. 553 00:24:18,120 --> 00:24:20,030 Maybe this is propanol. 554 00:24:20,030 --> 00:24:21,240 Right. 555 00:24:21,240 --> 00:24:25,330 Propane, glycerol, and so on. 556 00:24:25,330 --> 00:24:25,830 Yeah. 557 00:24:25,830 --> 00:24:28,230 But I'm still missing this concept. 558 00:24:28,230 --> 00:24:32,280 So I can now get dependence, but how do I get delta H? 559 00:24:32,280 --> 00:24:34,030 That's the next piece of the puzzle. 560 00:24:34,030 --> 00:24:34,530 Right. 561 00:24:34,530 --> 00:24:36,860 How do I get delta H? 562 00:24:36,860 --> 00:24:37,620 OK. 563 00:24:37,620 --> 00:24:41,590 So, you know, so far I've got this really cool result, right. 564 00:24:41,590 --> 00:24:44,370 I've got that P-- 565 00:24:44,370 --> 00:24:46,420 so far I've got that-- 566 00:24:46,420 --> 00:24:48,910 I'm going back to bowling-- 567 00:24:48,910 --> 00:24:50,170 I'm going back to boiling. 568 00:24:50,170 --> 00:24:50,670 Right. 569 00:24:50,670 --> 00:24:56,250 For boiling, I know that-- 570 00:24:56,250 --> 00:25:02,790 so the ion-- so P vapor is related to the IMFs, right. 571 00:25:02,790 --> 00:25:08,520 I know that P vapor is related to the temperature. 572 00:25:08,520 --> 00:25:14,470 And I know that the atmospheric pressure is important. 573 00:25:14,470 --> 00:25:14,970 Right. 574 00:25:14,970 --> 00:25:19,150 Atmospheric pressure is related to boiling. 575 00:25:19,150 --> 00:25:19,650 Yeah. 576 00:25:19,650 --> 00:25:19,860 OK. 577 00:25:19,860 --> 00:25:21,550 That's redundant, because you've got 578 00:25:21,550 --> 00:25:23,342 to get higher than the atmospheric pressure 579 00:25:23,342 --> 00:25:24,120 to boiling. 580 00:25:24,120 --> 00:25:26,400 That's how we defined it. 581 00:25:26,400 --> 00:25:30,090 So, but, again, this specific dependence 582 00:25:30,090 --> 00:25:32,160 is what I wanted on temperature, and I have it, 583 00:25:32,160 --> 00:25:34,740 except that I now need to know what this delta H is. 584 00:25:34,740 --> 00:25:37,020 OK. 585 00:25:37,020 --> 00:25:40,650 So here we go-- why is this related to pizza? 586 00:25:40,650 --> 00:25:43,470 Everything's related to pizza at the end of the day. 587 00:25:43,470 --> 00:25:47,250 But see, now we need to talk about delta H, 588 00:25:47,250 --> 00:25:49,950 and what it means. 589 00:25:49,950 --> 00:25:52,920 And you know, the way-- 590 00:25:52,920 --> 00:25:55,140 the easiest way to show what it means 591 00:25:55,140 --> 00:25:58,560 is to plot how this relates to phase change. 592 00:25:58,560 --> 00:26:02,830 How heat, right, that's how we're changing phase here 593 00:26:02,830 --> 00:26:03,970 with temperatures. 594 00:26:03,970 --> 00:26:05,350 We're changing the temperature. 595 00:26:05,350 --> 00:26:08,190 We're adding heat into the system. 596 00:26:08,190 --> 00:26:09,430 What does it do? 597 00:26:09,430 --> 00:26:10,460 What does it do? 598 00:26:10,460 --> 00:26:13,630 Well, you know, so one type of plot that you can make for that 599 00:26:13,630 --> 00:26:22,600 would be temperature versus thermal, thermal energy input. 600 00:26:22,600 --> 00:26:24,580 Now a lot of times what you'll see in textbooks 601 00:26:24,580 --> 00:26:26,560 is they call that q. 602 00:26:26,560 --> 00:26:27,920 It's an energy term. 603 00:26:27,920 --> 00:26:29,430 So it's like in joules, right. 604 00:26:29,430 --> 00:26:29,972 Let's say. 605 00:26:29,972 --> 00:26:31,930 But it's how much thermal energy you put it in, 606 00:26:31,930 --> 00:26:33,170 then you can draw it out like this. 607 00:26:33,170 --> 00:26:33,670 Right. 608 00:26:33,670 --> 00:26:37,450 So if you draw it out, then you would have your phases. 609 00:26:37,450 --> 00:26:42,070 So this would be like a gas, a liquid, a solid, and these 610 00:26:42,070 --> 00:26:43,060 would be phase changes. 611 00:26:46,420 --> 00:26:48,550 This, and that. 612 00:26:48,550 --> 00:26:52,240 So I'm adding thermal energy into the system. 613 00:26:52,240 --> 00:26:54,050 It's raising the temperature of the system. 614 00:26:54,050 --> 00:26:55,507 That's why these are going up. 615 00:26:55,507 --> 00:26:58,090 But the solid is getting hotter, and then, all of a sudden, it 616 00:26:58,090 --> 00:26:58,420 melts. 617 00:26:58,420 --> 00:26:58,690 OK. 618 00:26:58,690 --> 00:26:58,960 Good. 619 00:26:58,960 --> 00:26:59,590 So it melted. 620 00:26:59,590 --> 00:27:02,770 It melts. 621 00:27:02,770 --> 00:27:06,643 And then it's a liquid, and, all of a sudden, it vaporizes. 622 00:27:06,643 --> 00:27:07,910 Right. 623 00:27:07,910 --> 00:27:08,760 Vaporize. 624 00:27:08,760 --> 00:27:10,390 But you can go the other way. 625 00:27:10,390 --> 00:27:13,040 If you go the other way, it's condensation out here. 626 00:27:13,040 --> 00:27:13,540 All right. 627 00:27:13,540 --> 00:27:15,250 Or freezing in here. 628 00:27:15,250 --> 00:27:17,780 Melting, freezing, vaporization, condensation. 629 00:27:17,780 --> 00:27:20,290 But I like to draw it this way, because this way we're 630 00:27:20,290 --> 00:27:23,470 going to see very nicely what delta H is. 631 00:27:23,470 --> 00:27:25,960 So here's-- now I'm going to draw it with temperature 632 00:27:25,960 --> 00:27:27,110 on the x-axis. 633 00:27:27,110 --> 00:27:31,900 So temperature-- and this is going to be H. 634 00:27:31,900 --> 00:27:34,285 And I'm drawing this as the thermal energy-- 635 00:27:34,285 --> 00:27:36,570 let's see, I'm going to write it in the same terms-- 636 00:27:36,570 --> 00:27:37,070 right. 637 00:27:37,070 --> 00:27:38,530 So this is thermal energy. 638 00:27:38,530 --> 00:27:44,260 Now in this case, thermal energy, 639 00:27:44,260 --> 00:27:48,760 we use this thing called enthalpy, enthalpy. 640 00:27:48,760 --> 00:27:52,837 But you don't need to worry too much about it, for this class, 641 00:27:52,837 --> 00:27:54,670 you can think about it as the thermal energy 642 00:27:54,670 --> 00:27:56,780 content of the material. 643 00:27:56,780 --> 00:27:58,390 So if I have a change in that, wells, 644 00:27:58,390 --> 00:28:01,460 it's because I've lost or gained thermal energy. 645 00:28:01,460 --> 00:28:02,290 Right. 646 00:28:02,290 --> 00:28:03,910 If you take a thermal class, you'll 647 00:28:03,910 --> 00:28:06,220 learn a lot more about enthalpy. 648 00:28:06,220 --> 00:28:08,560 And that this is true only if you have constant pressure 649 00:28:08,560 --> 00:28:10,510 conditions, but that's not relevant here. 650 00:28:10,510 --> 00:28:14,360 I just want you to know, this is like this. 651 00:28:14,360 --> 00:28:15,050 OK. 652 00:28:15,050 --> 00:28:19,660 But this is the total thermal energy in your material. 653 00:28:19,660 --> 00:28:27,620 And by the way, you know, q, heat, the word heat is q. 654 00:28:27,620 --> 00:28:32,030 That is the definite-- heat means thermal energy transfer. 655 00:28:32,030 --> 00:28:35,750 Thermal energy transfer, a flow of heat. 656 00:28:35,750 --> 00:28:36,980 That makes sense. 657 00:28:36,980 --> 00:28:40,280 But you cannot say that this has 10 joules of heat. 658 00:28:40,280 --> 00:28:42,012 No, don't say that. 659 00:28:42,012 --> 00:28:43,970 You will sound like you're from another school. 660 00:28:43,970 --> 00:28:46,170 [LAUGHTER] 661 00:28:46,670 --> 00:28:50,330 You don't have-- you have that much enthalpy. 662 00:28:50,330 --> 00:28:50,900 Yeah. 663 00:28:50,900 --> 00:28:51,770 But not that much. 664 00:28:51,770 --> 00:28:54,500 Heat is a transfer of thermal energy, please. 665 00:28:57,090 --> 00:28:57,590 OK. 666 00:28:57,590 --> 00:28:58,860 Now here we go. 667 00:28:58,860 --> 00:28:59,360 All right. 668 00:28:59,360 --> 00:29:01,417 So let's suppose I were to draw this. 669 00:29:01,417 --> 00:29:03,000 Well, now I'm going to have the same-- 670 00:29:03,000 --> 00:29:04,250 I'm going to have phases. 671 00:29:04,250 --> 00:29:05,120 Right. 672 00:29:05,120 --> 00:29:08,240 And so here we go, here we go, here we go. 673 00:29:08,240 --> 00:29:11,570 And this is my gas, and this is my liquid, 674 00:29:11,570 --> 00:29:13,215 and this is my solid. 675 00:29:13,215 --> 00:29:14,840 There's a couple of cool things, right. 676 00:29:14,840 --> 00:29:18,020 So now-- so that's the thermal energy, H. 677 00:29:18,020 --> 00:29:20,420 But so now, if I were to take part 678 00:29:20,420 --> 00:29:24,170 of the solid like that, and just look at it, while it's a solid. 679 00:29:24,170 --> 00:29:27,350 I'm adding thermal energy to it. 680 00:29:27,350 --> 00:29:29,060 I'm increasing its temperature. 681 00:29:29,060 --> 00:29:30,560 We got a way to relate those things. 682 00:29:30,560 --> 00:29:32,780 It's called the heat capacity. 683 00:29:32,780 --> 00:29:34,040 All right. 684 00:29:34,040 --> 00:29:36,330 It's called the heat capacity. 685 00:29:36,330 --> 00:29:41,660 So if I look at that, OK, I can do that. 686 00:29:41,660 --> 00:29:43,090 Let's go here. 687 00:29:43,090 --> 00:29:43,850 All right. 688 00:29:43,850 --> 00:29:47,090 If I look at that, then I can relate those by-- 689 00:29:47,090 --> 00:29:49,790 well, I'm using q, because it's a change, right, that's 690 00:29:49,790 --> 00:29:51,690 the change in the enthalpy. 691 00:29:51,690 --> 00:29:52,190 All right. 692 00:29:52,190 --> 00:29:54,080 That's the energy transfer. 693 00:29:54,080 --> 00:29:56,960 It goes as the heat capacity times the change 694 00:29:56,960 --> 00:29:58,160 in the temperature. 695 00:29:58,160 --> 00:30:01,160 That s just means it's the heat capacity of the solid. 696 00:30:01,160 --> 00:30:05,480 Literally, that's the definition of heat capacity. 697 00:30:05,480 --> 00:30:07,160 Right. 698 00:30:07,160 --> 00:30:10,250 This would be like units of joules per kelvin. 699 00:30:10,250 --> 00:30:11,780 OK. 700 00:30:11,780 --> 00:30:15,390 So and, example of heat capacity, I love pizza, 701 00:30:15,390 --> 00:30:18,980 and so an example of heat capacity is the following. 702 00:30:18,980 --> 00:30:21,500 You burn, hopefully, you don't. 703 00:30:21,500 --> 00:30:24,050 But if you take it out of the oven, and you take a bite, 704 00:30:24,050 --> 00:30:26,330 right away, you will burn the roof of your mouth 705 00:30:26,330 --> 00:30:28,060 on the cheese. 706 00:30:28,060 --> 00:30:31,660 On the cheese, because cheese has a lot of water in it 707 00:30:31,660 --> 00:30:33,010 compared to the crust. 708 00:30:33,010 --> 00:30:37,280 And water has a really high heat capacity. 709 00:30:37,280 --> 00:30:38,360 What is heat capacity? 710 00:30:38,360 --> 00:30:42,560 It's the capacity of it to have thermal energy. 711 00:30:42,560 --> 00:30:45,710 And the water has a really high one, 712 00:30:45,710 --> 00:30:48,500 and so, when you take this out, everything's 713 00:30:48,500 --> 00:30:50,360 at the same temperature for just an instant. 714 00:30:50,360 --> 00:30:51,980 They're all at the same temperature. 715 00:30:51,980 --> 00:30:55,282 If you eat it right here, please don't, you 716 00:30:55,282 --> 00:30:57,740 burn your mouth on the crust the same way as on the cheese. 717 00:30:57,740 --> 00:30:59,420 But since you're waiting, now the crust 718 00:30:59,420 --> 00:31:01,378 gives out-- it doesn't have much heat capacity. 719 00:31:01,378 --> 00:31:02,570 So it all goes away. 720 00:31:02,570 --> 00:31:05,360 All that thermal energy leaves very quickly 721 00:31:05,360 --> 00:31:06,890 from the crust, but not the cheese, 722 00:31:06,890 --> 00:31:07,910 because it's got so much more. 723 00:31:07,910 --> 00:31:09,650 And if we want to get a little more serious about it, 724 00:31:09,650 --> 00:31:11,210 we can talk about the oceans. 725 00:31:11,210 --> 00:31:12,470 And so, I put this in here. 726 00:31:12,470 --> 00:31:14,870 Because we talk a lot about climate change, what 727 00:31:14,870 --> 00:31:18,050 you're talking about are the temperatures of the atmosphere. 728 00:31:18,050 --> 00:31:19,620 We talk about that a lot. 729 00:31:19,620 --> 00:31:21,050 But what gets sort of shoved aside 730 00:31:21,050 --> 00:31:25,910 is the temperature of the ocean, and that is rising, 731 00:31:25,910 --> 00:31:27,950 and it's not rising that quickly, luckily, 732 00:31:27,950 --> 00:31:30,830 but that's because the ocean has such a high heat capacity. 733 00:31:30,830 --> 00:31:34,670 That's where most of this thermal energy is going. 734 00:31:34,670 --> 00:31:37,430 It's going into the ocean. 735 00:31:37,430 --> 00:31:37,930 Right. 736 00:31:37,930 --> 00:31:39,555 And we need to start talking about that 737 00:31:39,555 --> 00:31:44,600 a whole lot more, because it's a lot higher than it used to be. 738 00:31:44,600 --> 00:31:48,620 This is the historical reference, pretty flat. 739 00:31:48,620 --> 00:31:53,940 A volcano erupts, 500 years ago, you get a blip this big. 740 00:31:53,940 --> 00:31:55,030 Now we're here. 741 00:31:55,030 --> 00:31:55,530 Right. 742 00:31:55,530 --> 00:31:58,590 So the amount of thermal energy this ocean is holding for us 743 00:31:58,590 --> 00:32:00,600 is very high. 744 00:32:00,600 --> 00:32:01,140 OK. 745 00:32:01,140 --> 00:32:02,340 Now so that's high capacity. 746 00:32:02,340 --> 00:32:04,430 That's kind of an important part, 747 00:32:04,430 --> 00:32:07,030 but, look, the other thing we have here-- ah, 748 00:32:07,030 --> 00:32:08,928 I keep hitting the wrong-- is this. 749 00:32:08,928 --> 00:32:10,470 And that's what I want to talk about. 750 00:32:10,470 --> 00:32:14,820 This is that delta H. Now in this case, 751 00:32:14,820 --> 00:32:18,180 it's the change in energy of fusion, 752 00:32:18,180 --> 00:32:20,010 because you're fusing to make a solid. 753 00:32:20,010 --> 00:32:23,066 In this case, it's called delta H of vaporization. 754 00:32:23,066 --> 00:32:27,606 You could call it condensation vaporization. 755 00:32:31,940 --> 00:32:33,230 That's the thing we needed. 756 00:32:33,230 --> 00:32:34,920 And now you see it so beautifully. 757 00:32:34,920 --> 00:32:35,420 All right. 758 00:32:35,420 --> 00:32:41,060 You see it so beautifully right there, because, now, you see-- 759 00:32:41,060 --> 00:32:45,140 so what is it that causes me to need to put a lot of energy 760 00:32:45,140 --> 00:32:49,730 into a material to change its bonds so that it can vaporize? 761 00:32:49,730 --> 00:32:52,310 It's all about the bonding strength. 762 00:32:52,310 --> 00:32:53,300 It's all about the-- 763 00:32:53,300 --> 00:32:55,080 everything comes to the bonding strength. 764 00:32:55,080 --> 00:32:55,580 Right. 765 00:32:55,580 --> 00:32:57,500 And so I have these kind of two things, right. 766 00:32:57,500 --> 00:33:02,360 Within one phase, within one phase, 767 00:33:02,360 --> 00:33:08,990 I can relate delta H to delta T. And that relationship is here. 768 00:33:08,990 --> 00:33:10,370 I'm in the solid phase. 769 00:33:10,370 --> 00:33:11,430 I can relate them. 770 00:33:11,430 --> 00:33:14,570 That's actually called sensible heat. 771 00:33:14,570 --> 00:33:17,145 Sensible heat. 772 00:33:17,145 --> 00:33:19,395 It's the energy that you would give off when you cool, 773 00:33:19,395 --> 00:33:22,370 or it's the energy that you'd absorb when you heat. 774 00:33:22,370 --> 00:33:24,630 But now I've got this other thing, 775 00:33:24,630 --> 00:33:28,180 which is at the phase change, at the phase change. 776 00:33:28,180 --> 00:33:29,930 Well, now, the temperature doesn't change, 777 00:33:29,930 --> 00:33:31,850 but I'm putting all of this energy 778 00:33:31,850 --> 00:33:34,010 in, or getting it all out. 779 00:33:34,010 --> 00:33:35,910 That's what delta H is. 780 00:33:35,910 --> 00:33:36,410 All right. 781 00:33:36,410 --> 00:33:40,430 So delta T is 0, because the temperature is constant. 782 00:33:40,430 --> 00:33:42,950 And delta H is sort of, generally, 783 00:33:42,950 --> 00:33:46,375 called the latent heat, latent heat. 784 00:33:46,375 --> 00:33:47,750 If you're talking about the phase 785 00:33:47,750 --> 00:33:49,167 change between a solid and liquid, 786 00:33:49,167 --> 00:33:51,860 it's the heat of fusion, heat of melting. 787 00:33:51,860 --> 00:33:55,415 If you're talking about between the liquid and gas 788 00:33:55,415 --> 00:33:56,665 vaporization, or condensation. 789 00:33:56,665 --> 00:33:58,200 So that's that energy change. 790 00:33:58,200 --> 00:34:02,190 And it's related to, well, what we've been talking about, 791 00:34:02,190 --> 00:34:03,800 but here it isn't a nice diagram. 792 00:34:03,800 --> 00:34:04,300 Right. 793 00:34:04,300 --> 00:34:07,350 Now, where do we go from here? 794 00:34:07,350 --> 00:34:09,350 Well, there's something so cool about this graph 795 00:34:09,350 --> 00:34:11,699 that I can show you really easily. 796 00:34:11,699 --> 00:34:13,830 I can also tell you how to do this, 797 00:34:13,830 --> 00:34:15,440 which is that things can-- 798 00:34:15,440 --> 00:34:18,320 these are the phase change transition temperatures, 799 00:34:18,320 --> 00:34:20,389 but things don't need to transition at those. 800 00:34:20,389 --> 00:34:24,400 In fact, oftentimes, you might get something like that. 801 00:34:24,400 --> 00:34:26,360 Not as much in the gas, but liquid to solid, 802 00:34:26,360 --> 00:34:27,650 you certainly can get it. 803 00:34:27,650 --> 00:34:30,530 This is called super cooled. 804 00:34:30,530 --> 00:34:31,190 Why? 805 00:34:31,190 --> 00:34:35,780 Because, for some reason, [INAUDIBLE],, for some reason, 806 00:34:35,780 --> 00:34:39,800 it's remained a liquid below its phase change temperature. 807 00:34:39,800 --> 00:34:42,020 Here's water, super cooled, poured into a glass. 808 00:34:42,020 --> 00:34:45,020 It's one of the most fun things you can do in life. 809 00:34:45,020 --> 00:34:46,100 There it is. 810 00:34:46,100 --> 00:34:47,213 It's a liquid. 811 00:34:47,213 --> 00:34:49,505 As soon as it hits the glass, it's like, wait a second, 812 00:34:49,505 --> 00:34:51,530 I want to be a solid. 813 00:34:51,530 --> 00:34:53,650 I'm over here. 814 00:34:53,650 --> 00:34:54,520 I'm over here. 815 00:34:54,520 --> 00:34:56,620 I need to be a solid. 816 00:34:56,620 --> 00:34:58,000 And you can do this. 817 00:34:58,000 --> 00:34:58,720 You can make-- 818 00:34:58,720 --> 00:35:01,000 I can tell you how to make it. 819 00:35:01,000 --> 00:35:03,430 You can make super cooled water at home. 820 00:35:03,430 --> 00:35:04,580 It's really fun. 821 00:35:04,580 --> 00:35:06,910 But that was what you're doing there, now you know, 822 00:35:06,910 --> 00:35:10,553 is you're bringing this down below the phase change. 823 00:35:10,553 --> 00:35:11,470 It's remaining liquid. 824 00:35:11,470 --> 00:35:13,095 Now all of a sudden, it hits the glass, 825 00:35:13,095 --> 00:35:14,380 and, but what am I doing? 826 00:35:14,380 --> 00:35:16,160 I need to solidify. 827 00:35:16,160 --> 00:35:17,140 All right. 828 00:35:17,140 --> 00:35:17,740 OK. 829 00:35:17,740 --> 00:35:21,570 This is the reason why all this matters is heat is a big deal. 830 00:35:21,570 --> 00:35:24,550 90%, you now, this is-- you can study this. 831 00:35:24,550 --> 00:35:26,170 There are wonderful charts to study. 832 00:35:26,170 --> 00:35:28,960 But depending on what you want to do, 833 00:35:28,960 --> 00:35:30,970 heat is almost always involved. 834 00:35:30,970 --> 00:35:34,510 Heat being a transfer of thermal energy. 835 00:35:34,510 --> 00:35:37,210 And so 90% of the current energy budget, 836 00:35:37,210 --> 00:35:40,860 basically, goes through the middle in some way. 837 00:35:40,860 --> 00:35:42,690 That's a lot. 838 00:35:42,690 --> 00:35:44,190 But then, if you look at things like 839 00:35:44,190 --> 00:35:47,660 this, which you shouldn't, because you can't read it, 840 00:35:47,660 --> 00:35:48,540 but if you blow up-- 841 00:35:48,540 --> 00:35:50,850 these are all the inputs on the left, 842 00:35:50,850 --> 00:35:52,770 all the ways we make energy. 843 00:35:52,770 --> 00:35:54,000 Here's how we use it. 844 00:35:54,000 --> 00:35:55,690 And here's the result. 845 00:35:55,690 --> 00:35:59,340 Here's where I want to get the punch line is, rejected energy. 846 00:35:59,340 --> 00:36:03,060 Whatever these units, doesn't matter, it's 60%. 847 00:36:03,060 --> 00:36:04,540 What is rejected energy mean? 848 00:36:04,540 --> 00:36:05,860 Wasted. 849 00:36:05,860 --> 00:36:08,080 All this precious fossil fuel stuff we're burning 850 00:36:08,080 --> 00:36:09,830 and all the solar energy we're collecting, 851 00:36:09,830 --> 00:36:13,570 anything we're doing here, 60% of it goes into heat, 852 00:36:13,570 --> 00:36:15,540 wasted heat. 853 00:36:15,540 --> 00:36:17,530 And so the reason why this matters 854 00:36:17,530 --> 00:36:19,360 is because there are these materials 855 00:36:19,360 --> 00:36:22,340 that we can use to try to capture some of that. 856 00:36:22,340 --> 00:36:22,840 Right. 857 00:36:22,840 --> 00:36:25,070 There are materials we can use to try to capture some of that, 858 00:36:25,070 --> 00:36:26,530 and it all comes down to chemistry. 859 00:36:26,530 --> 00:36:29,420 These are called phase change materials. 860 00:36:29,420 --> 00:36:32,856 And if you plot the melting temperature, that's this-- 861 00:36:32,856 --> 00:36:35,860 that's this melting temperature, right, Tm, 862 00:36:35,860 --> 00:36:41,260 versus how much of its delta H, how much delta H you have, 863 00:36:41,260 --> 00:36:43,600 you get all sorts of classes and materials. 864 00:36:43,600 --> 00:36:46,270 But, you know, so you might want a certain melting temperature 865 00:36:46,270 --> 00:36:48,520 from wherever you're operating, but then you might not 866 00:36:48,520 --> 00:36:50,622 get a high enough delta H, or you 867 00:36:50,622 --> 00:36:53,080 might want really high delta Hs, but then the thing doesn't 868 00:36:53,080 --> 00:36:55,820 melt until 700c, which is way too high. 869 00:36:55,820 --> 00:36:57,732 So we got to fill this out. 870 00:36:57,732 --> 00:36:58,690 We need materials here. 871 00:36:58,690 --> 00:36:59,648 We need materials here. 872 00:36:59,648 --> 00:37:01,910 That's a call to chemistry. 873 00:37:01,910 --> 00:37:03,680 That's a call to chemistry. 874 00:37:03,680 --> 00:37:06,470 So then, it all has to do with the phase change. 875 00:37:06,470 --> 00:37:07,310 It's a weird name. 876 00:37:07,310 --> 00:37:09,720 These are called phase change materials, 877 00:37:09,720 --> 00:37:12,530 but that's true of all materials. 878 00:37:12,530 --> 00:37:15,650 But, here, when you're talking about storing thermal energy, 879 00:37:15,650 --> 00:37:17,990 we use the term phase change materials. 880 00:37:17,990 --> 00:37:18,770 OK. 881 00:37:18,770 --> 00:37:22,520 Now the last concept, and I'll just touch on, and then 882 00:37:22,520 --> 00:37:28,650 spend a little time on Friday on, is the concept of a map. 883 00:37:28,650 --> 00:37:30,230 These are maps. 884 00:37:30,230 --> 00:37:31,490 These are maps. 885 00:37:31,490 --> 00:37:33,290 But you can go even bigger. 886 00:37:33,290 --> 00:37:38,162 And back in the day, back in the day, PVT was a big deal. 887 00:37:38,162 --> 00:37:39,620 You went to a party, you were going 888 00:37:39,620 --> 00:37:43,670 to talk about PVT. You were. 889 00:37:43,670 --> 00:37:45,710 And you know, and so, everybody had 890 00:37:45,710 --> 00:37:47,110 their own way of looking at it. 891 00:37:47,110 --> 00:37:48,590 Gay-Lussac, P versus T. 892 00:37:48,590 --> 00:37:52,340 But look, if I do P versus T, and hold volume 893 00:37:52,340 --> 00:37:55,520 constant, right, I might get like a line there, like P-- 894 00:37:55,520 --> 00:37:59,420 if this is pressure, all right, and this is temperature, 895 00:37:59,420 --> 00:38:02,600 you might get something like P versus T is a straight line, 896 00:38:02,600 --> 00:38:03,990 if you hold other stuff constant. 897 00:38:03,990 --> 00:38:04,160 Right. 898 00:38:04,160 --> 00:38:04,660 That's good. 899 00:38:04,660 --> 00:38:07,040 But that's not what I'm interested in today. 900 00:38:07,040 --> 00:38:10,610 I'm interested in where the phase boundaries are. 901 00:38:10,610 --> 00:38:11,310 Right. 902 00:38:11,310 --> 00:38:16,170 This is a materials map, and it gives me the boundary, 903 00:38:16,170 --> 00:38:18,988 that's what this is all about. 904 00:38:18,988 --> 00:38:20,280 That's what this was all about. 905 00:38:20,280 --> 00:38:23,580 Because, look, that's why I went through all this. 906 00:38:23,580 --> 00:38:24,510 You boil. 907 00:38:24,510 --> 00:38:25,340 What is boil? 908 00:38:25,340 --> 00:38:27,100 Phase change. 909 00:38:27,100 --> 00:38:27,690 Phase change. 910 00:38:27,690 --> 00:38:33,720 You boil when Pv is greater than P at [INAUDIBLE].. 911 00:38:33,720 --> 00:38:36,120 So that is the phase boundary. 912 00:38:36,120 --> 00:38:39,900 It's when you have both the gas and the liquid coexisting. 913 00:38:39,900 --> 00:38:40,920 Where is it? 914 00:38:45,040 --> 00:38:47,550 Ah, there it is, because I can get 915 00:38:47,550 --> 00:38:50,160 my pressure of vaporization, if I only 916 00:38:50,160 --> 00:38:52,750 know this, or vice versa. 917 00:38:52,750 --> 00:38:53,250 Right. 918 00:38:53,250 --> 00:38:56,550 And then I get that. 919 00:38:56,550 --> 00:38:57,390 It's up here. 920 00:38:57,390 --> 00:38:58,522 That's the phase boundary. 921 00:38:58,522 --> 00:39:00,730 Oh, yeah, that's all cool, but this is where it's at. 922 00:39:00,730 --> 00:39:03,360 I want to know where stuff changes phase. 923 00:39:03,360 --> 00:39:04,830 All right. 924 00:39:04,830 --> 00:39:06,510 And, of course, you can go further. 925 00:39:06,510 --> 00:39:08,730 And I've got to show you something here. 926 00:39:08,730 --> 00:39:10,480 There's a couple more things about-- these 927 00:39:10,480 --> 00:39:12,490 are called phase diagrams, right. 928 00:39:12,490 --> 00:39:16,720 These are maps of materials, and they are beautiful things, 929 00:39:16,720 --> 00:39:18,560 and incredibly important. 930 00:39:18,560 --> 00:39:21,400 And there's a couple last points, one of which 931 00:39:21,400 --> 00:39:25,330 I want to share now, and then the other I'll share on Friday. 932 00:39:25,330 --> 00:39:27,700 But the one I want to share now is the triple point. 933 00:39:27,700 --> 00:39:28,400 So look at this. 934 00:39:28,400 --> 00:39:30,130 Here's the gas liquid boundary line. 935 00:39:30,130 --> 00:39:32,080 That's what we've been talking about. 936 00:39:32,080 --> 00:39:33,970 You also got the solid liquid boundary line. 937 00:39:33,970 --> 00:39:35,410 That's here. 938 00:39:35,410 --> 00:39:37,360 You got gas liquid here, delta H- 939 00:39:37,360 --> 00:39:40,092 here's delta H. You also have sublimation. 940 00:39:40,092 --> 00:39:41,800 So you go straight from a solid to a gas, 941 00:39:41,800 --> 00:39:42,913 and you have deposition. 942 00:39:42,913 --> 00:39:44,830 You go straight from a gas-- but look at this. 943 00:39:44,830 --> 00:39:48,580 There's one point where they all co-exist. 944 00:39:48,580 --> 00:39:53,320 One, and only one where all three phases 945 00:39:53,320 --> 00:39:54,790 exist at the same time. 946 00:39:54,790 --> 00:39:55,900 That's pressure. 947 00:39:55,900 --> 00:39:57,670 That's temperature. 948 00:39:57,670 --> 00:40:01,120 And what's so cool about this is there's only one 949 00:40:01,120 --> 00:40:04,660 for this material, and so it, actually, is a really nice way 950 00:40:04,660 --> 00:40:08,440 to have a repeatable, reproducible point, which 951 00:40:08,440 --> 00:40:09,440 I'll get to in a second. 952 00:40:09,440 --> 00:40:11,320 But first you got to see this. 953 00:40:11,320 --> 00:40:13,210 This is a triple point. 954 00:40:13,210 --> 00:40:15,850 And what they're doing is they're 955 00:40:15,850 --> 00:40:17,830 lowering the pressure and the temperature. 956 00:40:17,830 --> 00:40:19,370 They're changing both. 957 00:40:19,370 --> 00:40:22,180 You could just do this with one or the other. 958 00:40:22,180 --> 00:40:23,110 Yeah. 959 00:40:23,110 --> 00:40:23,780 There it is. 960 00:40:23,780 --> 00:40:24,280 OK. 961 00:40:24,280 --> 00:40:25,510 How did they get it to boil? 962 00:40:25,510 --> 00:40:27,070 Lower the pressure. 963 00:40:27,070 --> 00:40:28,450 You now know why. 964 00:40:28,450 --> 00:40:31,720 You lower the atmosphere inside the container. 965 00:40:31,720 --> 00:40:34,430 You lowered that, so you went like this. 966 00:40:34,430 --> 00:40:35,602 You went down. 967 00:40:35,602 --> 00:40:37,810 And all of a sudden, you converted some of the liquid 968 00:40:37,810 --> 00:40:41,260 to gas, because you went down in pressure. 969 00:40:41,260 --> 00:40:43,330 And then you said, well, OK, but wait a second, 970 00:40:43,330 --> 00:40:45,680 I'm only seeing these two phases. 971 00:40:45,680 --> 00:40:49,210 So let me do this, and go over that way, getting 972 00:40:49,210 --> 00:40:52,150 closer, closer, OK, what's happening now? 973 00:40:52,150 --> 00:40:53,620 Then do this, right? 974 00:40:53,620 --> 00:40:57,180 And you're trying to find this special point here. 975 00:40:57,180 --> 00:40:58,810 And they're going close to it. 976 00:40:58,810 --> 00:41:00,130 They're going close to it. 977 00:41:00,130 --> 00:41:04,720 And then a couple minutes go by, that, look, it's freezing. 978 00:41:04,720 --> 00:41:06,050 It's freezing. 979 00:41:06,050 --> 00:41:10,130 It's-- but wait a second, I thought I said triple point. 980 00:41:10,130 --> 00:41:11,200 And I did. 981 00:41:11,200 --> 00:41:16,030 It's boiling and freezing at the same time. 982 00:41:16,030 --> 00:41:18,730 It is boiling and freezing at the same time. 983 00:41:18,730 --> 00:41:22,090 Yes, that is actually what all materials can do. 984 00:41:22,090 --> 00:41:23,140 That is incredible. 985 00:41:23,140 --> 00:41:24,460 Somebody just said what. 986 00:41:24,460 --> 00:41:27,100 Thank you for making my day. 987 00:41:27,100 --> 00:41:28,090 That makes my day. 988 00:41:28,090 --> 00:41:29,478 That is a triple point. 989 00:41:29,478 --> 00:41:32,020 We got a one or two more things to talk about phase diagrams. 990 00:41:32,020 --> 00:41:33,620 We'll do that on Friday. 991 00:41:33,620 --> 00:41:36,380 Have a great rest of your day. 992 00:41:36,380 --> 00:41:38,370 This is where we left off. 993 00:41:38,370 --> 00:41:40,160 And so, I want to start right here. 994 00:41:40,160 --> 00:41:42,970 And because a triple point is just so incredibly cool, 995 00:41:42,970 --> 00:41:45,642 I've found another random video, and I thought I'd show that. 996 00:41:45,642 --> 00:41:46,850 So this is where we left off. 997 00:41:46,850 --> 00:41:47,660 And here it is. 998 00:41:47,660 --> 00:41:50,075 And what they're doing, they might 999 00:41:50,075 --> 00:41:51,700 be controlling the temperature, they're 1000 00:41:51,700 --> 00:41:53,260 definitely controlling the pressure. 1001 00:41:53,260 --> 00:41:53,500 All right. 1002 00:41:53,500 --> 00:41:54,700 They have a liquid in here. 1003 00:41:54,700 --> 00:41:55,960 Now watch what happens. 1004 00:41:55,960 --> 00:41:58,840 We know now from the phase diagram 1005 00:41:58,840 --> 00:42:02,210 that you can find those boundaries on the diagram. 1006 00:42:02,210 --> 00:42:06,730 So they're lowering the pressure, and at some point, 1007 00:42:06,730 --> 00:42:08,280 yeah, nothing's going happen. 1008 00:42:08,280 --> 00:42:08,780 There. 1009 00:42:08,780 --> 00:42:09,280 OK. 1010 00:42:09,280 --> 00:42:10,210 Now it's playing. 1011 00:42:10,210 --> 00:42:12,910 And so at some point, this is going to start to freeze, 1012 00:42:12,910 --> 00:42:16,160 because I'm crossing over the boundary. 1013 00:42:16,160 --> 00:42:16,660 All right. 1014 00:42:16,660 --> 00:42:17,952 I'm crossing over the boundary. 1015 00:42:17,952 --> 00:42:21,340 And so when you cross over, when you get to a phase boundary, 1016 00:42:21,340 --> 00:42:23,900 you've got two phases coexisting. 1017 00:42:23,900 --> 00:42:25,360 Oh, and there it starts freezing, 1018 00:42:25,360 --> 00:42:27,490 so you've got the liquid and the solid phase coexisting, 1019 00:42:27,490 --> 00:42:28,060 but there's-- 1020 00:42:28,060 --> 00:42:31,300 but now can it coexist with, also, the gas. 1021 00:42:31,300 --> 00:42:34,400 And at one point of pressure and temperature, it can. 1022 00:42:34,400 --> 00:42:34,900 There it is. 1023 00:42:34,900 --> 00:42:36,540 It's kind of boiled a little bit. 1024 00:42:36,540 --> 00:42:39,340 I like this one, because it kind of goes big boil. 1025 00:42:39,340 --> 00:42:39,940 So here it is. 1026 00:42:39,940 --> 00:42:42,370 It's trying to freeze, and now it's boiling. 1027 00:42:42,370 --> 00:42:44,700 And now, watch, it'll refreeze. 1028 00:42:44,700 --> 00:42:45,800 All right. 1029 00:42:45,800 --> 00:42:47,590 And then it's going to boil again. 1030 00:42:47,590 --> 00:42:50,620 It's all three phases at exactly the same time. 1031 00:42:50,620 --> 00:42:51,760 So you can Google it. 1032 00:42:51,760 --> 00:42:51,910 There it is. 1033 00:42:51,910 --> 00:42:52,660 It boiled, again. 1034 00:42:52,660 --> 00:42:54,580 And then it's going to freeze, again. 1035 00:42:54,580 --> 00:42:57,310 It can do all three at once. 1036 00:42:57,310 --> 00:42:58,940 That is cool. 1037 00:42:58,940 --> 00:43:00,310 All right. 1038 00:43:00,310 --> 00:43:02,157 And how do we get there? 1039 00:43:02,157 --> 00:43:02,990 How do we get there? 1040 00:43:02,990 --> 00:43:04,497 Well, what I thought-- 1041 00:43:04,497 --> 00:43:06,580 on Wednesday was the first time I told you there's 1042 00:43:06,580 --> 00:43:07,660 two new lectures this fall. 1043 00:43:07,660 --> 00:43:09,220 That was the first time I gave that one. 1044 00:43:09,220 --> 00:43:10,040 That was one of them. 1045 00:43:10,040 --> 00:43:12,207 The other one will be on the chemistry of batteries. 1046 00:43:12,207 --> 00:43:14,750 And because it's new, I, you know, 1047 00:43:14,750 --> 00:43:16,630 I want to make sure that you feel 1048 00:43:16,630 --> 00:43:20,560 your oneness with the concepts that we learned. 1049 00:43:20,560 --> 00:43:23,380 And so I have made some summary slides 1050 00:43:23,380 --> 00:43:26,150 for you, that I'm not going to take time to go through. 1051 00:43:26,150 --> 00:43:27,880 But that tells you how we got to here. 1052 00:43:27,880 --> 00:43:30,160 That's the end of the lecture on Wednesday. 1053 00:43:30,160 --> 00:43:32,200 And I want to make sure that how we got there, 1054 00:43:32,200 --> 00:43:33,460 and what the key points were. 1055 00:43:33,460 --> 00:43:35,187 There are five key points. 1056 00:43:35,187 --> 00:43:37,520 And I've created a slide here, again, this is Wednesday, 1057 00:43:37,520 --> 00:43:38,810 so I'm not going to go through this in detail, 1058 00:43:38,810 --> 00:43:40,300 but I'll leave this in your notes. 1059 00:43:40,300 --> 00:43:43,300 One point was boiling and vapor pressure, and what that means. 1060 00:43:43,300 --> 00:43:46,970 The second point is the vapor pressure versus temperature, 1061 00:43:46,970 --> 00:43:51,220 which we get from kinetic theory and Clausius-Clapeyron gives us 1062 00:43:51,220 --> 00:43:53,980 the relationship between that vapor pressure 1063 00:43:53,980 --> 00:43:58,090 and the temperature through this thing called the vaporization. 1064 00:43:58,090 --> 00:44:00,340 The thermal-- this, remember, this change 1065 00:44:00,340 --> 00:44:02,310 in the thermal energy. 1066 00:44:02,310 --> 00:44:05,530 Right, this delta H, this change in enthalpy. 1067 00:44:05,530 --> 00:44:06,140 OK. 1068 00:44:06,140 --> 00:44:07,330 And by the way, you can-- 1069 00:44:07,330 --> 00:44:09,720 these are these like vapor pressure versus temperature 1070 00:44:09,720 --> 00:44:10,440 curves we drew. 1071 00:44:10,440 --> 00:44:12,090 You can take two of them, for example, 1072 00:44:12,090 --> 00:44:14,608 that gets rid of the constant in that equation, two 1073 00:44:14,608 --> 00:44:16,650 pressures, two vapor pressures, two temperatures. 1074 00:44:16,650 --> 00:44:18,990 You can calculate that vaporization energy. 1075 00:44:18,990 --> 00:44:21,000 That's that interrelationship we talked about. 1076 00:44:21,000 --> 00:44:23,610 The third point is the thermal energy 1077 00:44:23,610 --> 00:44:26,550 that delta H is related to the phase change. 1078 00:44:26,550 --> 00:44:28,420 It is the energy of the phase change. 1079 00:44:28,420 --> 00:44:28,920 Right. 1080 00:44:28,920 --> 00:44:30,330 So we talked about that. 1081 00:44:30,330 --> 00:44:32,100 And then, I couldn't find a good-- 1082 00:44:32,100 --> 00:44:35,760 so I just drew this myself here with fancy PowerPoint-- 1083 00:44:35,760 --> 00:44:37,980 and what you can see here is a heating curve. 1084 00:44:37,980 --> 00:44:39,730 And you can draw it in two different ways. 1085 00:44:39,730 --> 00:44:41,820 You can draw it as the temperature versus enthalpy, 1086 00:44:41,820 --> 00:44:43,237 or you could draw it as the energy 1087 00:44:43,237 --> 00:44:44,725 input versus temperature. 1088 00:44:44,725 --> 00:44:45,600 These are equivalent. 1089 00:44:45,600 --> 00:44:47,260 It's just not mm, and mm. 1090 00:44:47,260 --> 00:44:47,760 Right. 1091 00:44:47,760 --> 00:44:51,330 And then, in this, you can find all so much information, 1092 00:44:51,330 --> 00:44:54,200 like there's that delta H between the phases, right. 1093 00:44:54,200 --> 00:44:56,700 Here is the liquid phase, the gas, the solid. 1094 00:44:56,700 --> 00:44:58,380 And then, if you're in a single phase, 1095 00:44:58,380 --> 00:45:00,610 we talked about that change in enthalpy 1096 00:45:00,610 --> 00:45:02,650 related to the heat capacity. 1097 00:45:02,650 --> 00:45:05,280 If you're at the phase change, the temperature doesn't change, 1098 00:45:05,280 --> 00:45:07,300 but you're putting a lot of energy into it. 1099 00:45:07,300 --> 00:45:09,270 And that, finally, got us to phase diagrams. 1100 00:45:09,270 --> 00:45:10,780 This is where we left off. 1101 00:45:10,780 --> 00:45:14,480 So I'm leaving this all here for you to look at if you want. 1102 00:45:14,480 --> 00:45:16,620 It's kind of a summary of Wednesday's lecture, 1103 00:45:16,620 --> 00:45:17,850 the key points. 1104 00:45:17,850 --> 00:45:19,360 This is that two-phase curve. 1105 00:45:19,360 --> 00:45:19,860 Right. 1106 00:45:19,860 --> 00:45:21,930 And this is-- on these curves, remember, 1107 00:45:21,930 --> 00:45:24,180 the phase diagram is a map. 1108 00:45:24,180 --> 00:45:26,970 It's this beautiful map of the material. 1109 00:45:26,970 --> 00:45:27,480 Right. 1110 00:45:27,480 --> 00:45:30,810 It's a map of the chemistry of the thermodynamics 1111 00:45:30,810 --> 00:45:33,260 of the phases of whether it's a gas, liquid, or solid. 1112 00:45:33,260 --> 00:45:37,380 And these coexistence curves are where two phases coexist. 1113 00:45:37,380 --> 00:45:38,000 Right. 1114 00:45:38,000 --> 00:45:40,020 So you see at these temperatures and pressures, 1115 00:45:40,020 --> 00:45:43,800 and that's why we started the lecture talking about vapor 1116 00:45:43,800 --> 00:45:47,610 pressure, because the vapor pressure is such a nice way 1117 00:45:47,610 --> 00:45:51,540 to get into the idea of how a material changes phase 1118 00:45:51,540 --> 00:45:54,880 from liquid to gas, which is what we did. 1119 00:45:54,880 --> 00:45:56,970 And then, we also talked about how 1120 00:45:56,970 --> 00:45:59,387 that triple point, that's the video that we left off with. 1121 00:45:59,387 --> 00:46:01,428 And then there's one last thing I didn't mention, 1122 00:46:01,428 --> 00:46:03,420 which is that there's this critical point here. 1123 00:46:03,420 --> 00:46:04,950 What's happening out there? 1124 00:46:04,950 --> 00:46:08,310 What's happening out there is really interesting, too. 1125 00:46:08,310 --> 00:46:12,000 There is a temperature, right, above which-- 1126 00:46:12,000 --> 00:46:14,800 so there is-- if you keep going up in temperature, 1127 00:46:14,800 --> 00:46:17,850 there is a critical point where this boundary just disappears. 1128 00:46:17,850 --> 00:46:19,480 It stops. 1129 00:46:19,480 --> 00:46:21,510 The liquid, there's the liquid, and the gas, 1130 00:46:21,510 --> 00:46:23,880 and now there's no line. 1131 00:46:23,880 --> 00:46:24,950 What happened? 1132 00:46:24,950 --> 00:46:27,480 What happened is, you've reached a temperature 1133 00:46:27,480 --> 00:46:32,070 where it, basically, can't exist as a liquid anymore. 1134 00:46:32,070 --> 00:46:36,530 If you keep going, the thermal energy is just too high. 1135 00:46:36,530 --> 00:46:38,760 But the pressure is too high, too. 1136 00:46:38,760 --> 00:46:41,470 So this is a different phase. 1137 00:46:41,470 --> 00:46:44,730 And this phase it out here is called supercritical. 1138 00:46:44,730 --> 00:46:46,860 This is called supercritical, where the material 1139 00:46:46,860 --> 00:46:49,880 has properties of both. 1140 00:46:49,880 --> 00:46:50,880 That's really cool. 1141 00:46:50,880 --> 00:46:51,380 Right. 1142 00:46:51,380 --> 00:46:53,430 So this material has maybe properties 1143 00:46:53,430 --> 00:46:56,220 like it can flow like a gas, all right, 1144 00:46:56,220 --> 00:46:58,140 but it's got a higher density than a gas, 1145 00:46:58,140 --> 00:47:01,170 but it's still lighter than a liquid. 1146 00:47:01,170 --> 00:47:02,990 And it's that same material. 1147 00:47:02,990 --> 00:47:05,760 It's that same material, whatever it is, water. 1148 00:47:05,760 --> 00:47:06,570 Right. 1149 00:47:06,570 --> 00:47:07,760 That's called supercritical. 1150 00:47:07,760 --> 00:47:10,510 So these lines can end like that. 1151 00:47:10,510 --> 00:47:12,690 And that's called the critical point. 1152 00:47:12,690 --> 00:47:15,570 Now, there, you know, there are many reasons 1153 00:47:15,570 --> 00:47:17,280 why these maps are important. 1154 00:47:17,280 --> 00:47:20,190 I thought I'd give you one which is strawberries. 1155 00:47:20,190 --> 00:47:22,740 Because, if you go and you buy-- 1156 00:47:22,740 --> 00:47:25,275 some of us like to buy like dried fruit-- 1157 00:47:25,275 --> 00:47:27,900 but if I take strawberries and I leave them out on the counter, 1158 00:47:27,900 --> 00:47:30,580 they're not going to look like this. 1159 00:47:30,580 --> 00:47:32,090 You know, how do you know that? 1160 00:47:32,090 --> 00:47:33,882 Well, you know that from the phase diagram, 1161 00:47:33,882 --> 00:47:37,350 because if I draw my temperature and pressure, 1162 00:47:37,350 --> 00:47:42,900 and I've got some phase diagram that looks like this, right. 1163 00:47:42,900 --> 00:47:47,130 And so now, you know solid, liquid, gas. 1164 00:47:47,130 --> 00:47:48,870 Well, you know, I could-- 1165 00:47:48,870 --> 00:47:53,320 if I just-- if I just tried to dry these things out, 1166 00:47:53,320 --> 00:47:55,304 that's this. 1167 00:47:55,304 --> 00:47:56,830 That's that. 1168 00:47:56,830 --> 00:48:00,690 But so, I'm-- maybe, maybe, I'm going to, or maybe I want to do 1169 00:48:00,690 --> 00:48:01,190 this. 1170 00:48:01,190 --> 00:48:02,820 Oh, that's even worse. 1171 00:48:02,820 --> 00:48:04,807 What if I go like this. 1172 00:48:04,807 --> 00:48:06,390 I'm going to heat the strawberries up. 1173 00:48:06,390 --> 00:48:08,310 I'm making jam. 1174 00:48:08,310 --> 00:48:08,820 No. 1175 00:48:08,820 --> 00:48:10,090 That's not jam. 1176 00:48:10,090 --> 00:48:10,590 Right. 1177 00:48:10,590 --> 00:48:13,020 That's nice kind of maybe still solid, 1178 00:48:13,020 --> 00:48:16,110 it's not like mushy and gooey. 1179 00:48:16,110 --> 00:48:17,300 How do I get it? 1180 00:48:17,300 --> 00:48:19,680 Well, you use the phase diagram, of course. 1181 00:48:19,680 --> 00:48:23,730 You go-- because this kind of phase change, 1182 00:48:23,730 --> 00:48:25,860 going across that phase boundary, 1183 00:48:25,860 --> 00:48:29,130 it creates a lot of disruption in the material. 1184 00:48:29,130 --> 00:48:30,630 It creates a lot of disruption. 1185 00:48:30,630 --> 00:48:32,740 You saw it, right, this boiling. 1186 00:48:32,740 --> 00:48:36,180 So if you do that for the water inside of the strawberries, 1187 00:48:36,180 --> 00:48:41,670 you're going to destroy all the framework of the good stuff, 1188 00:48:41,670 --> 00:48:43,710 right. 1189 00:48:43,710 --> 00:48:45,570 So what you do is you freeze it. 1190 00:48:45,570 --> 00:48:49,290 You go this way, and then you go that way. 1191 00:48:49,290 --> 00:48:53,520 If you do that, now the solid as it 1192 00:48:53,520 --> 00:48:56,370 sublimates is much less of a kind 1193 00:48:56,370 --> 00:48:59,370 of violent, disturbing phenomenon 1194 00:48:59,370 --> 00:49:02,130 to the surrounding matrix of strawberry. 1195 00:49:02,130 --> 00:49:04,650 And so you get these freeze dried fruit that way. 1196 00:49:04,650 --> 00:49:09,060 It's much less disturbing, destructive way 1197 00:49:09,060 --> 00:49:10,060 to get rid of the water. 1198 00:49:10,060 --> 00:49:11,185 That's called freeze dried. 1199 00:49:11,185 --> 00:49:13,630 You can also go the other-- if I go out here, 1200 00:49:13,630 --> 00:49:18,430 I've got all sorts of uses to use this supercritical region. 1201 00:49:18,430 --> 00:49:21,490 I've got all sorts of ways where that becomes useful. 1202 00:49:21,490 --> 00:49:22,990 That's how coffee is decaffeinated, 1203 00:49:22,990 --> 00:49:25,280 because it's a different phase of this material. 1204 00:49:25,280 --> 00:49:27,580 So the phase maps give us this information. 1205 00:49:27,580 --> 00:49:32,080 They tell us how we can engineer properties and materials 1206 00:49:32,080 --> 00:49:33,840 by engineering their phases. 1207 00:49:33,840 --> 00:49:35,370 Right. 1208 00:49:35,370 --> 00:49:38,830 And if you pull out another thing, you know-- 1209 00:49:38,830 --> 00:49:40,690 a lot of the textbooks and what we did 1210 00:49:40,690 --> 00:49:42,585 is we look at the phase diagram down here. 1211 00:49:42,585 --> 00:49:43,960 But if you pull out, you also can 1212 00:49:43,960 --> 00:49:46,100 see how complex materials are. 1213 00:49:46,100 --> 00:49:46,600 All right. 1214 00:49:46,600 --> 00:49:48,227 This is water. 1215 00:49:48,227 --> 00:49:50,310 We've been focusing on this part of phase diagram, 1216 00:49:50,310 --> 00:49:51,460 now you plot it. 1217 00:49:51,460 --> 00:49:57,900 Water has 17 phases, 17, not 3. 1218 00:49:57,900 --> 00:50:00,360 And just two years ago, the 17th was discovered, 1219 00:50:00,360 --> 00:50:03,650 and it's a very, very light form of ice. 1220 00:50:03,650 --> 00:50:04,160 All right. 1221 00:50:04,160 --> 00:50:07,975 So you can get all sorts of really important information 1222 00:50:07,975 --> 00:50:10,100 about materials by looking at their phase diagrams. 1223 00:50:10,100 --> 00:50:11,600 You can compare different materials, 1224 00:50:11,600 --> 00:50:15,620 like this is the phase diagram of CO2 versus water. 1225 00:50:15,620 --> 00:50:17,900 And you can learn about sort of where 1226 00:50:17,900 --> 00:50:19,250 their critical points are. 1227 00:50:19,250 --> 00:50:22,460 You can see all the slope here in water is-- 1228 00:50:22,460 --> 00:50:24,830 most material slope like that. 1229 00:50:24,830 --> 00:50:26,210 Water slopes like that. 1230 00:50:26,210 --> 00:50:27,973 And that's because of hydrogen bonds. 1231 00:50:27,973 --> 00:50:29,390 Because the hydrogen bonds make it 1232 00:50:29,390 --> 00:50:33,980 so that the solid is less dense than the liquid, which means, 1233 00:50:33,980 --> 00:50:36,920 if I squeeze on it, I can-- 1234 00:50:36,920 --> 00:50:38,510 then I go to the liquid. 1235 00:50:38,510 --> 00:50:40,010 That's really weird. 1236 00:50:40,010 --> 00:50:42,770 If I squeeze on this, it's more soft. 1237 00:50:42,770 --> 00:50:45,970 But here, it goes-- it can cross a phase boundary. 1238 00:50:45,970 --> 00:50:48,610 That's very unique to water, and the fish 1239 00:50:48,610 --> 00:50:52,390 are very happy about that, because ice floats. 1240 00:50:52,390 --> 00:50:53,190 OK. 1241 00:50:53,190 --> 00:50:56,590 Now, OK, now, so that's the kind of last part of the phase 1242 00:50:56,590 --> 00:50:58,470 diagram stuff.