1 00:00:16,449 --> 00:00:17,317 How's everyone doing? 2 00:00:17,317 --> 00:00:18,952 [STUDENTS CHEERING] 3 00:00:18,952 --> 00:00:21,154 It's a goody bag. 4 00:00:21,154 --> 00:00:23,523 Thank you for that. 5 00:00:23,523 --> 00:00:24,657 It's a goody bag day. 6 00:00:24,657 --> 00:00:25,525 It's a good day. 7 00:00:29,229 --> 00:00:34,234 Related to the goody bags, once again-- hello. 8 00:00:34,234 --> 00:00:36,770 Once again, I want to get these out 9 00:00:36,770 --> 00:00:39,105 for you, because you got to have them on a Friday night. 10 00:00:39,105 --> 00:00:41,608 There's no real better way to think 11 00:00:41,608 --> 00:00:44,010 about spending your time on a Friday night 12 00:00:44,010 --> 00:00:46,646 than opening up a brand new goody bag. 13 00:00:46,646 --> 00:00:51,051 The topic of the goody bag is related 14 00:00:51,051 --> 00:00:53,753 to reactions, which is the topic we're starting today. 15 00:00:53,753 --> 00:00:58,224 But it's really also related to acids and bases, 16 00:00:58,224 --> 00:01:00,727 which is something we'll talk about on Monday. 17 00:01:00,727 --> 00:01:02,362 So I'm giving you the goody bag today, 18 00:01:02,362 --> 00:01:04,897 but I'll talk about the goody bag 19 00:01:04,897 --> 00:01:07,934 and contextualize it in the lecture on Monday. 20 00:01:10,170 --> 00:01:11,971 But as I said, today what we're going to do 21 00:01:11,971 --> 00:01:15,141 is we're going to start a new topic that we'll 22 00:01:15,141 --> 00:01:17,544 be talking about for the next couple of weeks. 23 00:01:17,544 --> 00:01:20,013 And that is the topic of reactions. 24 00:01:20,013 --> 00:01:22,015 And what we're going to talk about is reactions, OK? 25 00:01:22,015 --> 00:01:26,553 Now this falls under the domain of something 26 00:01:26,553 --> 00:01:29,289 called chemical kinetics, which is 27 00:01:29,289 --> 00:01:32,092 this study of reaction rates. 28 00:01:32,092 --> 00:01:34,761 Kinetic, move, right? 29 00:01:34,761 --> 00:01:36,729 So what's moving? 30 00:01:36,729 --> 00:01:38,465 Concentration, right? 31 00:01:38,465 --> 00:01:42,902 This stuff that you started with is doing something and winding 32 00:01:42,902 --> 00:01:44,771 up different. 33 00:01:44,771 --> 00:01:46,339 That's a reaction, OK? 34 00:01:46,339 --> 00:01:49,008 Now we've already written lots of reactions in this class, 35 00:01:49,008 --> 00:01:53,513 but today, we're going to talk about the rates. 36 00:01:53,513 --> 00:01:56,515 And the rate in particular is the changing concentration 37 00:01:56,515 --> 00:01:59,018 of the reactions and products with time. 38 00:01:59,018 --> 00:02:01,121 So there's a couple of terms that we 39 00:02:01,121 --> 00:02:04,624 got to know because we're going to be working with them. 40 00:02:04,624 --> 00:02:07,560 So I'm going to start by writing those down. 41 00:02:07,560 --> 00:02:10,630 So the first thing is the thing that we're 42 00:02:10,630 --> 00:02:15,101 going to talk about changing, which is the concentration. 43 00:02:15,101 --> 00:02:24,310 So the concentration is equal to the moles per liter. 44 00:02:24,310 --> 00:02:26,679 I mean, there are lots of ways to write concentration. 45 00:02:26,679 --> 00:02:28,548 This is the way we're going to write it, 46 00:02:28,548 --> 00:02:31,417 moles of a substance per liter. 47 00:02:31,417 --> 00:02:32,685 Well, that has a name for it. 48 00:02:32,685 --> 00:02:35,021 That's called them the molarity. 49 00:02:35,021 --> 00:02:36,089 What's molarity? 50 00:02:36,089 --> 00:02:39,192 It's moles per liter. 51 00:02:39,192 --> 00:02:41,861 And then we can also write it in shorthand, 52 00:02:41,861 --> 00:02:47,734 which I'll be doing as simply some substance in brackets. 53 00:02:47,734 --> 00:02:53,139 If I say that I have some substance A, and now I say, 54 00:02:53,139 --> 00:02:55,742 oh, look, I'm writing brackets around it, 55 00:02:55,742 --> 00:02:59,646 then what I mean is the concentration of A, OK? 56 00:02:59,646 --> 00:03:00,914 That's what that means. 57 00:03:00,914 --> 00:03:04,584 Which is the moles per liter of A. 58 00:03:04,584 --> 00:03:05,985 Good, so that's concentration. 59 00:03:05,985 --> 00:03:06,486 What else? 60 00:03:06,486 --> 00:03:07,554 Well, there's the rate. 61 00:03:07,554 --> 00:03:08,988 There is the rate. 62 00:03:08,988 --> 00:03:13,660 And the rate is, as you might guess, the change 63 00:03:13,660 --> 00:03:17,363 in the concentration with time. 64 00:03:17,363 --> 00:03:19,799 That's the rate that we're going to be talking about a lot 65 00:03:19,799 --> 00:03:21,834 today, the reaction rate. 66 00:03:21,834 --> 00:03:24,304 There's a change in the concentration with time. 67 00:03:24,304 --> 00:03:25,305 What else do we got? 68 00:03:25,305 --> 00:03:28,141 Well, we have then a law. 69 00:03:28,141 --> 00:03:35,781 Because see, here's the thing, the rate is just the rate. 70 00:03:35,781 --> 00:03:38,384 It's the change with something with time, right? 71 00:03:38,384 --> 00:03:40,987 It's like the change in distance with time 72 00:03:40,987 --> 00:03:42,388 would be like velocity. 73 00:03:42,388 --> 00:03:44,557 OK, but what if I wanted to say, well, 74 00:03:44,557 --> 00:03:49,896 could you tell me what the rate is as some function? 75 00:03:49,896 --> 00:03:51,598 Right, as some function? 76 00:03:51,598 --> 00:03:53,266 That's called the rate law. 77 00:03:53,266 --> 00:03:54,400 That's called the rate law. 78 00:03:54,400 --> 00:04:00,306 And it will give me a rate versus concentration. 79 00:04:00,306 --> 00:04:03,176 That's what I want out of a rate law. 80 00:04:03,176 --> 00:04:06,913 And then, well, I could integrate that. 81 00:04:06,913 --> 00:04:09,515 I could integrate that because the rate 82 00:04:09,515 --> 00:04:11,618 itself is a derivative with time. 83 00:04:11,618 --> 00:04:12,552 It's a change in time. 84 00:04:12,552 --> 00:04:14,454 So if I integrate it, well then I've 85 00:04:14,454 --> 00:04:17,557 got something called the integrated rate law. 86 00:04:17,557 --> 00:04:24,130 Integrated rate law. 87 00:04:24,130 --> 00:04:25,531 And what's that going to give me? 88 00:04:25,531 --> 00:04:29,836 It's going to give me the concentration versus time. 89 00:04:33,473 --> 00:04:35,875 So the rate law is a rate versus concentration. 90 00:04:35,875 --> 00:04:40,613 And the integrated rate law is the concentration versus time. 91 00:04:40,613 --> 00:04:43,082 And then we've got Arrhenius. 92 00:04:43,082 --> 00:04:44,951 Let's put it all on the same board. 93 00:04:44,951 --> 00:04:50,390 So I'll do one more here, which is the Arrhenius 94 00:04:50,390 --> 00:04:55,995 dependence for reactions. 95 00:04:55,995 --> 00:04:59,732 And as you might guess, this is going to give me 96 00:04:59,732 --> 00:05:05,972 rate versus temperature. 97 00:05:05,972 --> 00:05:08,474 These are the things we're going to be talking about. 98 00:05:08,474 --> 00:05:10,410 These are all the things-- all of these things 99 00:05:10,410 --> 00:05:13,646 we're going to talk about today in the context of reactions. 100 00:05:13,646 --> 00:05:15,882 I wanted to get them all down on the board 101 00:05:15,882 --> 00:05:18,618 so you can see them and think about them 102 00:05:18,618 --> 00:05:22,555 and feel them as we go forward. 103 00:05:22,555 --> 00:05:25,457 So there are a whole bunch of things 104 00:05:25,457 --> 00:05:29,696 that impact the reaction, the rate of a reaction. 105 00:05:29,696 --> 00:05:30,730 What is it that matters? 106 00:05:30,730 --> 00:05:31,864 Well, concentration. 107 00:05:31,864 --> 00:05:33,332 How much do you have? 108 00:05:33,332 --> 00:05:35,802 That's the brackets thing, right? 109 00:05:35,802 --> 00:05:40,840 Temperature, catalysts, the surface 110 00:05:40,840 --> 00:05:44,077 and the structure that you're doing the reaction on, 111 00:05:44,077 --> 00:05:46,679 the solvent that it's in. 112 00:05:46,679 --> 00:05:49,982 All of these things impact how the reaction happens. 113 00:05:49,982 --> 00:05:52,452 As you can see, I grayed out, made a little darker 114 00:05:52,452 --> 00:05:55,088 those bottom two because I'm not going to talk about those two. 115 00:05:55,088 --> 00:05:58,391 But I will talk about each of those other items today. 116 00:05:58,391 --> 00:05:59,459 That's our goal. 117 00:05:59,459 --> 00:06:03,463 How do those items play into these dependencies? 118 00:06:03,463 --> 00:06:05,698 That's our goal, to figure that out. 119 00:06:05,698 --> 00:06:09,235 OK, so we're going to start with concentration. 120 00:06:09,235 --> 00:06:11,804 And we're going to talk about how concentration 121 00:06:11,804 --> 00:06:14,207 plays a role in reaction rates. 122 00:06:14,207 --> 00:06:16,609 And we're going to start with something very simple. 123 00:06:16,609 --> 00:06:20,880 I have something called A. Oh, it's purple. 124 00:06:20,880 --> 00:06:24,584 And it turns into something called B. It's green. 125 00:06:24,584 --> 00:06:25,184 There you go. 126 00:06:25,184 --> 00:06:26,853 There's a reaction. 127 00:06:26,853 --> 00:06:28,654 OK, so let's start-- 128 00:06:28,654 --> 00:06:33,926 OK, so aA goes to bB. 129 00:06:33,926 --> 00:06:38,965 Now the very first thing that I can think about in this 130 00:06:38,965 --> 00:06:42,101 is that nothing is lost. 131 00:06:42,101 --> 00:06:45,004 Nothing is lost. 132 00:06:45,004 --> 00:06:47,407 So I'm going to assume that nothing 133 00:06:47,407 --> 00:06:49,509 disappeared from my container. 134 00:06:49,509 --> 00:06:50,042 You see that? 135 00:06:50,042 --> 00:06:51,811 The container is there. 136 00:06:51,811 --> 00:06:54,213 So I haven't lost any mass. 137 00:06:54,213 --> 00:06:55,548 I haven't lost any mass. 138 00:06:55,548 --> 00:06:59,252 Well, mass conservation is a big deal, right? 139 00:06:59,252 --> 00:07:03,556 So mass conservation-- by taking this very simple case, 140 00:07:03,556 --> 00:07:06,159 mass conser-- 141 00:07:06,159 --> 00:07:08,561 oh, really? 142 00:07:08,561 --> 00:07:11,564 We could have a mass conversation too. 143 00:07:11,564 --> 00:07:12,165 That's OK. 144 00:07:12,165 --> 00:07:14,100 That's kind of what we're doing. 145 00:07:14,100 --> 00:07:16,436 But let's write it as conservation. 146 00:07:16,436 --> 00:07:20,907 This means that if I take away A, 147 00:07:20,907 --> 00:07:25,611 I must add B with the same amount and not lose anything. 148 00:07:25,611 --> 00:07:28,948 And if you look at that in terms of these coefficients, 149 00:07:28,948 --> 00:07:33,052 remember, these are stoichiometric coefficients 150 00:07:33,052 --> 00:07:34,454 as part of the reaction. 151 00:07:34,454 --> 00:07:39,392 Then what that means is that 1 over b 152 00:07:39,392 --> 00:07:45,665 times the change in the concentration of B with time 153 00:07:45,665 --> 00:07:50,303 must equal minus 1 over a times the change 154 00:07:50,303 --> 00:07:53,473 in concentration of A with time. 155 00:07:53,473 --> 00:07:56,008 That is mass conservation, just written 156 00:07:56,008 --> 00:08:01,714 as changes in concentration. 157 00:08:01,714 --> 00:08:02,849 You can see it. 158 00:08:02,849 --> 00:08:05,284 Look, imagine just as-- 159 00:08:08,154 --> 00:08:13,059 imagine that this is 1, just as an example, OK? 160 00:08:13,059 --> 00:08:19,999 1H2 goes to 2H, right? 161 00:08:19,999 --> 00:08:21,300 I'm not going to lose anything. 162 00:08:21,300 --> 00:08:23,503 Those are my stoichio-- well, OK, 163 00:08:23,503 --> 00:08:26,405 this would tell you that the rate of this 164 00:08:26,405 --> 00:08:29,175 if I don't lose anything would be 165 00:08:29,175 --> 00:08:36,182 1/2 the change in H, the concentration of H with time 166 00:08:36,182 --> 00:08:39,919 equals minus the change in concentration of H2. 167 00:08:39,919 --> 00:08:44,757 That's just exactly what I wrote, but with an example. 168 00:08:44,757 --> 00:08:45,992 I didn't lose anything, right? 169 00:08:45,992 --> 00:08:48,694 So the rate of change of this must be twice the rate 170 00:08:48,694 --> 00:08:50,963 of change at that, right? 171 00:08:50,963 --> 00:08:55,835 Stoichiometric coefficients come in and they make sure-- 172 00:08:55,835 --> 00:08:57,303 when I write it this way, they make 173 00:08:57,303 --> 00:08:59,572 sure I don't lose anything. 174 00:08:59,572 --> 00:09:01,507 That's why you've got to have these there. 175 00:09:01,507 --> 00:09:04,944 Now there's a couple other things about this, all right? 176 00:09:04,944 --> 00:09:08,314 There's a couple other things about this. 177 00:09:08,314 --> 00:09:16,222 One is that you'll notice that the rate is always positive. 178 00:09:16,222 --> 00:09:18,391 Maybe we should write that up on the top board. 179 00:09:18,391 --> 00:09:20,927 Because it's a convention. 180 00:09:20,927 --> 00:09:24,163 But we like positive numbers when we talk about rate. 181 00:09:24,163 --> 00:09:29,702 So the rate is always positive, OK? 182 00:09:29,702 --> 00:09:32,171 Always positive. 183 00:09:32,171 --> 00:09:34,473 So when we have-- 184 00:09:34,473 --> 00:09:35,975 when we're thinking about a reaction 185 00:09:35,975 --> 00:09:39,211 where something's getting consumed, 186 00:09:39,211 --> 00:09:41,414 we're going to write it as the negative of the change 187 00:09:41,414 --> 00:09:42,348 in that concentration. 188 00:09:42,348 --> 00:09:43,816 Because that's a negative, and then 189 00:09:43,816 --> 00:09:46,352 we're going to write it as a positive of the change 190 00:09:46,352 --> 00:09:48,754 in concentration of things being formed, OK? 191 00:09:48,754 --> 00:09:52,558 So the rate is written as positive. 192 00:09:52,558 --> 00:09:54,193 Well, there is another thing, which 193 00:09:54,193 --> 00:09:56,262 is we can go more general. 194 00:09:56,262 --> 00:09:57,430 Let's just think about this. 195 00:09:57,430 --> 00:10:01,968 If we go more general, more general, 196 00:10:01,968 --> 00:10:04,837 then let's have more than just A to B. 197 00:10:04,837 --> 00:10:13,512 Let's have aA plus bB goes to cC plus dD. 198 00:10:13,512 --> 00:10:15,314 So now I've got four things. 199 00:10:15,314 --> 00:10:18,417 Two products, two reactants, right? 200 00:10:18,417 --> 00:10:21,087 OK A and B are the reactants, C and D are the products. 201 00:10:21,087 --> 00:10:24,657 And they've all got their coefficients. 202 00:10:24,657 --> 00:10:29,228 And so you can look at the change in any one of these 203 00:10:29,228 --> 00:10:31,263 and know the rate. 204 00:10:31,263 --> 00:10:33,332 You could look at the change in any one of these 205 00:10:33,332 --> 00:10:34,333 and know the rate. 206 00:10:34,333 --> 00:10:39,905 So if I look at this, then the rate would be equal to minus 1 207 00:10:39,905 --> 00:10:41,674 over a, great convention. 208 00:10:41,674 --> 00:10:44,877 OK, it's a positive value. 209 00:10:44,877 --> 00:10:51,017 That's got to be equal to minus 1 over b times the change in B 210 00:10:51,017 --> 00:10:51,617 with time. 211 00:10:51,617 --> 00:10:57,289 And it must be equal to plus 1 over C, times the change in C 212 00:10:57,289 --> 00:10:58,057 with time. 213 00:10:58,057 --> 00:11:00,059 And that also must be equal to plus 1 214 00:11:00,059 --> 00:11:05,931 over d, all right, times the change in the concentration d 215 00:11:05,931 --> 00:11:08,567 change dt. 216 00:11:08,567 --> 00:11:11,103 Right? 217 00:11:11,103 --> 00:11:14,273 So I could look at the way any one of these things 218 00:11:14,273 --> 00:11:18,344 is disappearing or forming and because those stoichiometric 219 00:11:18,344 --> 00:11:21,580 coefficients are there, I know what the rate of that reaction 220 00:11:21,580 --> 00:11:22,314 is. 221 00:11:22,314 --> 00:11:29,321 Again, this is basically a statement of mass conservation. 222 00:11:29,321 --> 00:11:32,324 Ah, but there's more because this is just 223 00:11:32,324 --> 00:11:33,993 a definition of rate. 224 00:11:33,993 --> 00:11:38,664 Rate is changing concentration and it's always positive, done. 225 00:11:38,664 --> 00:11:40,900 But I want a law. 226 00:11:40,900 --> 00:11:43,969 I want to know not just OK, yeah, 227 00:11:43,969 --> 00:11:46,639 I see how you change with time so that's a rate. 228 00:11:46,639 --> 00:11:49,208 But I want to know a law, that if I gave you 229 00:11:49,208 --> 00:11:53,179 any concentration, if I gave you any set of concentrations, 230 00:11:53,179 --> 00:11:55,214 what would the rate be? 231 00:11:55,214 --> 00:11:56,248 What would the rate be? 232 00:11:56,248 --> 00:11:58,350 Could I come up with a function? 233 00:11:58,350 --> 00:12:04,623 And so we write down the rate as depending 234 00:12:04,623 --> 00:12:07,126 on the concentrations. 235 00:12:07,126 --> 00:12:09,295 Now, you can do this with the products or reactants. 236 00:12:09,295 --> 00:12:11,564 We're going to do this with the reactants. 237 00:12:11,564 --> 00:12:14,133 And so you would have that it depends 238 00:12:14,133 --> 00:12:17,670 on the concentrations of a and b raised 239 00:12:17,670 --> 00:12:20,139 to some power with some coefficient. 240 00:12:20,139 --> 00:12:24,977 So k times a concentration of A to the m 241 00:12:24,977 --> 00:12:28,247 times the concentration of B to the n. 242 00:12:28,247 --> 00:12:30,449 OK, so we're raising these-- 243 00:12:30,449 --> 00:12:34,553 Now, we don't know what these are, but what we're saying 244 00:12:34,553 --> 00:12:37,857 is that there's got to be a way if I just know, 245 00:12:37,857 --> 00:12:40,259 and maybe if I do some experiments or something, 246 00:12:40,259 --> 00:12:43,095 maybe I could come up with a general function that 247 00:12:43,095 --> 00:12:46,232 depends on just the concentrations, wherever 248 00:12:46,232 --> 00:12:47,833 they are of a and b. 249 00:12:47,833 --> 00:12:49,802 And they're going to be raised to some exponent 250 00:12:49,802 --> 00:12:51,604 that I don't know yet and they're 251 00:12:51,604 --> 00:12:54,006 going to have some constant. 252 00:12:54,006 --> 00:12:55,441 That's a rate law. 253 00:12:55,441 --> 00:12:56,442 That's a rate. 254 00:12:56,442 --> 00:12:57,943 OK? 255 00:12:57,943 --> 00:13:03,082 Now, OK, the thing is that the rate law-- 256 00:13:03,082 --> 00:13:05,451 let's go over to here. 257 00:13:05,451 --> 00:13:05,951 OK. 258 00:13:05,951 --> 00:13:09,922 So the k is, as you can imagine going 259 00:13:09,922 --> 00:13:13,159 to be very important here, that's called a rate constant. 260 00:13:13,159 --> 00:13:14,827 K is equal to a rate constant. 261 00:13:20,466 --> 00:13:25,271 And this is going to depend on conditions like temperature, 262 00:13:25,271 --> 00:13:26,939 pressure, solvent. 263 00:13:26,939 --> 00:13:29,308 So it's going to depend on things like temperature, 264 00:13:29,308 --> 00:13:33,279 pressure, solvent, et cetera. 265 00:13:33,279 --> 00:13:34,013 All right? 266 00:13:34,013 --> 00:13:38,117 And we'll see how you get k. 267 00:13:38,117 --> 00:13:41,787 But m and n cannot come-- and this is very important-- 268 00:13:41,787 --> 00:13:46,792 m and n and k for that matter must come-- 269 00:13:46,792 --> 00:13:48,561 Gesundheit. 270 00:13:48,561 --> 00:13:52,198 --from experiments. 271 00:13:52,198 --> 00:13:54,667 They're determined experimentally, 272 00:13:54,667 --> 00:13:58,537 determined experiments. 273 00:13:58,537 --> 00:13:59,038 OK? 274 00:14:02,975 --> 00:14:06,011 This is a mistake that is often made. 275 00:14:06,011 --> 00:14:09,582 You see, m and n must somehow be related to these coefficients. 276 00:14:09,582 --> 00:14:10,282 No. 277 00:14:10,282 --> 00:14:12,618 M and n is something else. 278 00:14:12,618 --> 00:14:15,754 I've created a function that the rate depends on, 279 00:14:15,754 --> 00:14:17,890 the rate of this reaction depends on. 280 00:14:17,890 --> 00:14:19,558 I've put these exponents in there 281 00:14:19,558 --> 00:14:22,995 and I'm looking for the dependents on m and n. 282 00:14:22,995 --> 00:14:24,964 And the only way to do that, to know that, 283 00:14:24,964 --> 00:14:26,699 is to do experiments. 284 00:14:26,699 --> 00:14:29,468 You can't just get that from the way the reaction is written. 285 00:14:29,468 --> 00:14:34,273 You can get mass conservation and the relationship 286 00:14:34,273 --> 00:14:37,743 between rate, rate, rate. 287 00:14:37,743 --> 00:14:38,510 Right? 288 00:14:38,510 --> 00:14:40,579 Those are all the same. 289 00:14:40,579 --> 00:14:43,883 But you can't get the rate law unless you 290 00:14:43,883 --> 00:14:45,050 do some measurements. 291 00:14:45,050 --> 00:14:48,787 Now, then when you do, then you can 292 00:14:48,787 --> 00:14:51,190 get the order of the reaction. 293 00:14:51,190 --> 00:14:55,961 So this is the reaction order and that's 294 00:14:55,961 --> 00:15:03,269 an important property. 295 00:15:03,269 --> 00:15:04,970 There's one more thing I'll say, and then 296 00:15:04,970 --> 00:15:07,606 what we're going to do, I'm setting the stage here 297 00:15:07,606 --> 00:15:09,174 and then we're going to do examples. 298 00:15:09,174 --> 00:15:09,675 OK? 299 00:15:09,675 --> 00:15:12,578 So don't worry, we're going to go through different examples 300 00:15:12,578 --> 00:15:17,917 that I think will help crystallize these concepts. 301 00:15:17,917 --> 00:15:20,519 But the last thing I want to say in terms of setting the stage 302 00:15:20,519 --> 00:15:25,391 is that the units of rate, if you 303 00:15:25,391 --> 00:15:27,192 look at how I've defined the units of rate, 304 00:15:27,192 --> 00:15:30,996 it's a change in concentration with time. 305 00:15:30,996 --> 00:15:39,638 So the units of rate, the units of rate 306 00:15:39,638 --> 00:15:45,878 are going to be molarity over time. 307 00:15:45,878 --> 00:15:48,914 That doesn't change. 308 00:15:48,914 --> 00:15:49,682 Right? 309 00:15:49,682 --> 00:15:53,419 That doesn't change, those are the units of rate. 310 00:15:53,419 --> 00:15:55,654 That's the definition of the rate. 311 00:15:55,654 --> 00:15:58,424 But you can see, and we will see, 312 00:15:58,424 --> 00:16:02,494 that if that has to always be true, then the units of k 313 00:16:02,494 --> 00:16:04,363 may very. 314 00:16:04,363 --> 00:16:08,000 And we're going to see that as we go through examples. 315 00:16:08,000 --> 00:16:12,237 So the units of k could be different and we'll be 316 00:16:12,237 --> 00:16:15,774 depending on the reaction order, which is basically saying 317 00:16:15,774 --> 00:16:18,777 it depends on the rate law. 318 00:16:18,777 --> 00:16:21,347 OK, setting the stage. 319 00:16:21,347 --> 00:16:23,415 Now, let's look at some examples. 320 00:16:23,415 --> 00:16:25,317 And we're going to go through this sequential, 321 00:16:25,317 --> 00:16:27,219 we're going to do a zeroth order reaction, 322 00:16:27,219 --> 00:16:30,389 than a first order reaction, and then a second order reaction. 323 00:16:30,389 --> 00:16:30,990 OK? 324 00:16:30,990 --> 00:16:32,024 So zeroth order. 325 00:16:32,024 --> 00:16:36,028 Well, zeroth order reaction, right? 326 00:16:36,028 --> 00:16:37,763 So this is nitrous oxide. 327 00:16:37,763 --> 00:16:43,602 So this is a reaction of nitrous oxide turning into N2 and O2. 328 00:16:43,602 --> 00:16:48,307 Nitrous oxide is used in many, many applications, 329 00:16:48,307 --> 00:16:49,641 not just laughing gas. 330 00:16:53,912 --> 00:16:57,649 If we go with what we just wrote down. 331 00:16:57,649 --> 00:16:59,284 OK, so let's take this example, I'm 332 00:16:59,284 --> 00:17:00,719 going to write it down here. 333 00:17:00,719 --> 00:17:08,260 2 N20 goes to 2 N2 plus O2. 334 00:17:08,260 --> 00:17:09,428 OK. 335 00:17:09,428 --> 00:17:11,864 Well, so the rate we know from what I wrote down, 336 00:17:11,864 --> 00:17:17,036 the rate is equal to minus 1/2 times the change 337 00:17:17,036 --> 00:17:20,138 in the concentration of N20 with time. 338 00:17:24,309 --> 00:17:26,979 But see, so now I'm doing some measurements 339 00:17:26,979 --> 00:17:30,516 and I'm plotting some data here. 340 00:17:30,516 --> 00:17:36,188 So I'm plotting here the concentration of all three 341 00:17:36,188 --> 00:17:40,392 of these, the reaction, and the two products with time. 342 00:17:40,392 --> 00:17:43,595 And what you notice is if I plot the concentration with time, 343 00:17:43,595 --> 00:17:46,165 it's a linear relationship. 344 00:17:46,165 --> 00:17:48,967 What does that mean? 345 00:17:48,967 --> 00:17:53,038 That means that they don't depend on concentration 346 00:17:53,038 --> 00:17:56,942 because the rate is the change right, 347 00:17:56,942 --> 00:17:59,945 the rate is the change in those with time, right? 348 00:17:59,945 --> 00:18:02,114 The change in the concentration of time 349 00:18:02,114 --> 00:18:05,350 is always the same because it's a straight line. 350 00:18:05,350 --> 00:18:12,825 So if that's true, then the rate from, 351 00:18:12,825 --> 00:18:16,562 let's say, straight line, straight line, 352 00:18:16,562 --> 00:18:18,730 and we'll talk about plots as we go, 353 00:18:18,730 --> 00:18:26,738 straight line plot of concentration versus time. 354 00:18:26,738 --> 00:18:28,941 All right, straight line plot, then we 355 00:18:28,941 --> 00:18:42,654 know that concentration is independent of time. 356 00:18:42,654 --> 00:18:43,155 I'm sorry. 357 00:18:45,724 --> 00:18:49,061 Rate is independent. 358 00:18:49,061 --> 00:18:50,095 OK, hold on. 359 00:18:50,095 --> 00:18:54,566 Rate is independent of concentration. 360 00:18:54,566 --> 00:18:55,868 OK. 361 00:18:55,868 --> 00:18:59,004 The rate in the beginning is the change in concentration. 362 00:18:59,004 --> 00:19:00,539 The rate in the middle is the change 363 00:19:00,539 --> 00:19:02,808 in concentration with time and it's a straight line 364 00:19:02,808 --> 00:19:05,611 so it's always the same. 365 00:19:05,611 --> 00:19:06,979 Well, that means something. 366 00:19:06,979 --> 00:19:09,882 It means something in terms of our rate law. 367 00:19:09,882 --> 00:19:13,418 Because now I know from my rate law, 368 00:19:13,418 --> 00:19:17,890 that the rate is equal to k, the rate constant, 369 00:19:17,890 --> 00:19:22,761 times N20 to the m. 370 00:19:22,761 --> 00:19:24,396 That's from here, right? 371 00:19:24,396 --> 00:19:26,765 You take all the reactants and you put them down 372 00:19:26,765 --> 00:19:28,700 and you put exponents on them. 373 00:19:28,700 --> 00:19:33,639 And so I've just got one, N20 and it's raised to the m. 374 00:19:33,639 --> 00:19:37,342 Yeah, but I know there's no concentration dependents 375 00:19:37,342 --> 00:19:38,010 of this rate. 376 00:19:38,010 --> 00:19:42,014 So I know that m equals zero and it's 377 00:19:42,014 --> 00:19:47,553 a zeroth order reaction, rxn. 378 00:19:47,553 --> 00:19:51,723 Oh, I've saved so much time, rxn reaction, 379 00:19:51,723 --> 00:19:55,460 which means that the rate is simply equal to k. 380 00:19:55,460 --> 00:19:57,963 The rate must equal k, OK? 381 00:20:00,732 --> 00:20:05,704 So in this case the rate, right, so we're continuing here 382 00:20:05,704 --> 00:20:07,472 equals k. 383 00:20:07,472 --> 00:20:21,186 And that means that k must have units of molarity over time. 384 00:20:21,186 --> 00:20:24,690 Why, because that's the units of rate, the units of rate 385 00:20:24,690 --> 00:20:27,859 don't change, the units of k will. 386 00:20:27,859 --> 00:20:31,530 But in a zeroth order reaction, the units of k 387 00:20:31,530 --> 00:20:35,067 have to be equal to the units of rate 388 00:20:35,067 --> 00:20:37,336 that there's nothing else in there. 389 00:20:37,336 --> 00:20:38,303 OK. 390 00:20:38,303 --> 00:20:39,805 Again, I want to emphasize, there 391 00:20:39,805 --> 00:20:43,375 is no simple correlation between the stoichiometry, 392 00:20:43,375 --> 00:20:47,479 the coefficients of these things and the rate law, 393 00:20:47,479 --> 00:20:48,814 you've got to do experiments. 394 00:20:48,814 --> 00:20:50,215 This data comes from-- 395 00:20:50,215 --> 00:20:53,885 Well look at it, there's the mass conservation in action, 396 00:20:53,885 --> 00:20:56,622 02, N2, all right? 397 00:20:56,622 --> 00:20:57,923 You can see it. 398 00:20:57,923 --> 00:21:00,058 You can feel it. 399 00:21:00,058 --> 00:21:04,730 Slopes are different, they must be. 400 00:21:04,730 --> 00:21:07,899 Now, here's a reaction some of you may care about. 401 00:21:07,899 --> 00:21:11,270 So why does a zeroth order reaction matter. 402 00:21:11,270 --> 00:21:15,040 Why does it matter, because that's the reaction of beer. 403 00:21:17,943 --> 00:21:20,579 So ethanol, OK, but we'll call it beer. 404 00:21:20,579 --> 00:21:23,215 So what does this mean? 405 00:21:23,215 --> 00:21:28,520 If I consume beer, if I did, then the concentration 406 00:21:28,520 --> 00:21:33,392 of ethanol in it, there it is plotted versus time is linear. 407 00:21:33,392 --> 00:21:35,727 That means, this is very important, 408 00:21:35,727 --> 00:21:38,163 it's a zeroth order reaction. 409 00:21:38,163 --> 00:21:40,932 It means if I plot the rate of the reaction, you see it? 410 00:21:40,932 --> 00:21:41,433 There it is. 411 00:21:41,433 --> 00:21:46,438 It's a constant, it doesn't depend on the concentration. 412 00:21:46,438 --> 00:21:49,241 But that really has a lot of ramifications, 413 00:21:49,241 --> 00:21:52,411 because if I drink a lot of beer, the average 70 kilogram 414 00:21:52,411 --> 00:21:57,482 person, it takes 2 and 1/2 hours for the enzymes in their liver 415 00:21:57,482 --> 00:22:02,587 to decompose 15 milliliters of ethanol, one beer. 416 00:22:05,090 --> 00:22:06,792 But look at that, so that means that if I 417 00:22:06,792 --> 00:22:11,830 had more than that the body, it's not 418 00:22:11,830 --> 00:22:14,099 dependent on how much I have. 419 00:22:14,099 --> 00:22:18,403 The reaction of the liver, the enzymes 420 00:22:18,403 --> 00:22:19,905 that are breaking this down is not 421 00:22:19,905 --> 00:22:21,206 dependent on the concentration. 422 00:22:21,206 --> 00:22:24,109 So if I load up a lot more in there it doesn't matter. 423 00:22:24,109 --> 00:22:25,877 There is a pipeline and there's a rate 424 00:22:25,877 --> 00:22:32,284 and it's not changing, well that leads to consequences 425 00:22:32,284 --> 00:22:35,387 to be thought about when you drink beer. 426 00:22:35,387 --> 00:22:37,322 But there's another thing we can do with beer, 427 00:22:37,322 --> 00:22:39,291 which is we can integrate it. 428 00:22:39,291 --> 00:22:40,759 Right? 429 00:22:40,759 --> 00:22:47,366 Because if we know that beer-- 430 00:22:47,366 --> 00:22:48,333 if we know that minus-- 431 00:22:48,333 --> 00:22:50,535 I'm going to say there's some reaction that beer goes 432 00:22:50,535 --> 00:22:51,169 to something. 433 00:22:51,169 --> 00:22:59,411 So minus d beer, dt OK? 434 00:22:59,411 --> 00:23:01,513 Assuming it has a coefficient of 1, 435 00:23:01,513 --> 00:23:08,153 is going to equal, that's going to equal k because it's 436 00:23:08,153 --> 00:23:09,988 a zeroth order reaction. 437 00:23:09,988 --> 00:23:11,556 Right, it's a constant. 438 00:23:11,556 --> 00:23:14,926 And so OK, now I integrate both sides. 439 00:23:14,926 --> 00:23:19,598 If I integrate, then I've got the integrated right law 440 00:23:19,598 --> 00:23:23,935 for beer, which is that the concentration of beer 441 00:23:23,935 --> 00:23:31,009 is equal to some initial concentration of beer minus kt. 442 00:23:31,009 --> 00:23:33,211 This is the integrated rate law. 443 00:23:33,211 --> 00:23:34,312 That's the integrated law. 444 00:23:34,312 --> 00:23:36,715 Notice what I've done, I've gone from talking 445 00:23:36,715 --> 00:23:39,851 about the rate of the beer being the rate there, 446 00:23:39,851 --> 00:23:44,055 which is a constant to a dependence. 447 00:23:44,055 --> 00:23:45,490 There it is, integrated rate law. 448 00:23:45,490 --> 00:23:48,927 The promise was that would get me a concentration versus time 449 00:23:48,927 --> 00:23:52,330 and that's what it did, concentration versus time. 450 00:23:52,330 --> 00:23:53,131 How did I get it? 451 00:23:53,131 --> 00:23:57,235 Well, I had a rate law and I integrated it. 452 00:23:57,235 --> 00:23:58,703 And I'm not going through the math, 453 00:23:58,703 --> 00:24:02,240 but you put the dt over here and you integrate, OK? 454 00:24:02,240 --> 00:24:03,074 OK. 455 00:24:03,074 --> 00:24:05,277 So that's an integrated rate law. 456 00:24:05,277 --> 00:24:07,245 Well, let's go to the next order. 457 00:24:07,245 --> 00:24:11,450 If I had first order and I looked at the data for that, 458 00:24:11,450 --> 00:24:17,589 then you would see if I plot the concentration versus time 459 00:24:17,589 --> 00:24:19,658 it would not be a straight line. 460 00:24:19,658 --> 00:24:20,692 Why? 461 00:24:20,692 --> 00:24:22,994 Well, because for a first order reaction, 462 00:24:22,994 --> 00:24:24,229 so now we're in first order. 463 00:24:28,733 --> 00:24:35,674 Right, then what that means is that the exponent here is a 1 464 00:24:35,674 --> 00:24:39,478 or if I have two reactants, the addition of them, 465 00:24:39,478 --> 00:24:46,151 it's first order total or it might 466 00:24:46,151 --> 00:24:48,987 be dependent on two reactants and its first order 467 00:24:48,987 --> 00:24:51,556 in each of them, but then second order overall because they're 468 00:24:51,556 --> 00:24:52,791 multiplied. 469 00:24:52,791 --> 00:24:56,728 Let's stay we the simpler case of just one reactant A. 470 00:24:56,728 --> 00:25:00,432 So if there's one reactant, and let's suppose 471 00:25:00,432 --> 00:25:04,002 A goes to some product. 472 00:25:04,002 --> 00:25:07,739 I'm not even going to write it out. 473 00:25:07,739 --> 00:25:12,544 You know that the rate is equal to minus 474 00:25:12,544 --> 00:25:18,750 the change in the concentration of A with time 475 00:25:18,750 --> 00:25:21,453 and that because it's first order 476 00:25:21,453 --> 00:25:27,058 it depends on the concentration raised to the first power. 477 00:25:27,058 --> 00:25:30,028 That's what we said first order meant, right. 478 00:25:30,028 --> 00:25:32,597 I'm telling you this is first order now. 479 00:25:32,597 --> 00:25:33,098 OK. 480 00:25:35,734 --> 00:25:38,036 Well, you can see that if it's first order 481 00:25:38,036 --> 00:25:40,171 it depends on the concentration. 482 00:25:40,171 --> 00:25:42,240 And so that means that you can see from that 483 00:25:42,240 --> 00:25:43,475 and you can see from the plot. 484 00:25:43,475 --> 00:25:48,847 If the concentration of A doubles the rate doubles. 485 00:25:48,847 --> 00:25:49,614 The rate doubles. 486 00:25:49,614 --> 00:25:53,818 Why can't our livers do that. 487 00:25:53,818 --> 00:25:55,887 No, they're zeroth order, but there 488 00:25:55,887 --> 00:25:57,689 are lots of reactions that are first order. 489 00:26:00,959 --> 00:26:04,095 OK, here's the thing right, but the rate still 490 00:26:04,095 --> 00:26:08,800 has to have units of molarity change with time, right 491 00:26:08,800 --> 00:26:11,269 molarity over time. 492 00:26:11,269 --> 00:26:16,808 They can't have that unless k units are k units, 493 00:26:16,808 --> 00:26:22,981 in this case, are going to be-- 494 00:26:22,981 --> 00:26:25,250 So let's see, let me write down-- 495 00:26:25,250 --> 00:26:30,388 OK rate has units. 496 00:26:30,388 --> 00:26:35,994 The overall units are molarity over time. 497 00:26:35,994 --> 00:26:41,299 So now I've got k times molarity, 498 00:26:41,299 --> 00:26:45,103 that has to have units of molarity over time 499 00:26:45,103 --> 00:26:48,807 and so k must have units of 1 over time. 500 00:26:48,807 --> 00:26:56,247 1 over time, but that tells us what the plot. 501 00:26:56,247 --> 00:26:58,750 It helps tell us things about like-- 502 00:26:58,750 --> 00:27:01,886 But the plots always come better when we integrate. 503 00:27:01,886 --> 00:27:05,757 If we think about the integrated rate law, 504 00:27:05,757 --> 00:27:11,763 then it leads to linearity, which is something 505 00:27:11,763 --> 00:27:13,298 we always want in plots. 506 00:27:13,298 --> 00:27:14,332 Linear lines. 507 00:27:14,332 --> 00:27:15,400 Straight lines. 508 00:27:15,400 --> 00:27:18,036 Linear lines, really, I just said that? 509 00:27:18,036 --> 00:27:19,471 I did just say that. 510 00:27:19,471 --> 00:27:23,708 I'm OK with it because it's true. 511 00:27:23,708 --> 00:27:26,878 But let's integrate this. 512 00:27:26,878 --> 00:27:30,915 Integrated rate law. 513 00:27:30,915 --> 00:27:33,051 So now, there's my right law. 514 00:27:33,051 --> 00:27:35,587 Now I'm going to take the dt over and the concentration over 515 00:27:35,587 --> 00:27:38,456 and I'm going to integrate and I get this, 516 00:27:38,456 --> 00:27:44,062 A equals some initial concentration times e 517 00:27:44,062 --> 00:27:47,165 to the minus kt. 518 00:27:47,165 --> 00:27:49,000 Notice the units, right 1 over time. 519 00:27:49,000 --> 00:27:50,301 That's good. 520 00:27:50,301 --> 00:27:52,404 OK, or if you want, you could say 521 00:27:52,404 --> 00:28:00,211 that that's a Ln A equals Ln a 0 minus kt 522 00:28:00,211 --> 00:28:03,081 and this right now, this gave it to me. 523 00:28:03,081 --> 00:28:08,653 Because now you know that if you plot Ln versus time, 524 00:28:08,653 --> 00:28:16,461 if I have a plot of Ln versus time, plot of Ln versus time, 525 00:28:16,461 --> 00:28:17,495 then it's linear. 526 00:28:17,495 --> 00:28:22,567 And we like linear and that's what's plotted on the right. 527 00:28:22,567 --> 00:28:24,703 So that's a plot of Ln versus time. 528 00:28:24,703 --> 00:28:27,005 And so you can kind of go backwards and forth. 529 00:28:27,005 --> 00:28:33,078 Like if I had a linear plot with concentration versus time 530 00:28:33,078 --> 00:28:35,013 you know it's zeroth order. 531 00:28:35,013 --> 00:28:38,349 If I had a linear plot with Ln concentration versus time 532 00:28:38,349 --> 00:28:40,351 you know it's first order. 533 00:28:40,351 --> 00:28:42,787 And you know that from the integrated rate law. 534 00:28:46,057 --> 00:28:54,666 Now, if you have data, how do I know what the rate law-- 535 00:28:54,666 --> 00:28:57,802 I'm sorry, what the reaction order is. 536 00:28:57,802 --> 00:29:00,205 Often you'll just have data, you study a reaction 537 00:29:00,205 --> 00:29:01,072 and you get data. 538 00:29:01,072 --> 00:29:03,341 Here's a very important reaction. 539 00:29:03,341 --> 00:29:06,244 This molecule is called cisplatin. 540 00:29:06,244 --> 00:29:10,348 Now, cisplatin is maybe the most used 541 00:29:10,348 --> 00:29:13,485 and one of the certainly, very most important chemotherapy 542 00:29:13,485 --> 00:29:15,253 drugs. 543 00:29:15,253 --> 00:29:17,856 But it's not active in this state 544 00:29:17,856 --> 00:29:19,124 with the two chlorine's there. 545 00:29:19,124 --> 00:29:24,028 You've got to get one of them out and put a water molecule 546 00:29:24,028 --> 00:29:27,766 there, so that with the water molecule 547 00:29:27,766 --> 00:29:30,602 it can go and damage the DNA of the tumor. 548 00:29:30,602 --> 00:29:34,939 That's the idea and it can't do that unless this reaction 549 00:29:34,939 --> 00:29:36,508 happens in the body. 550 00:29:36,508 --> 00:29:39,177 And so you can imagine that this kind of reaction 551 00:29:39,177 --> 00:29:40,478 is extremely important. 552 00:29:40,478 --> 00:29:41,379 What? 553 00:29:41,379 --> 00:29:45,650 And the rate is extremely important here, all right. 554 00:29:45,650 --> 00:29:49,087 This has to happen in a time frame that we know very well. 555 00:29:49,087 --> 00:29:51,356 So this rate has been studied very carefully 556 00:29:51,356 --> 00:29:52,123 for this reaction. 557 00:29:52,123 --> 00:29:53,892 And you can see, OK, you can write down 558 00:29:53,892 --> 00:29:56,327 numbers, how much did I start with 559 00:29:56,327 --> 00:29:59,831 and how much what was the rate, and I'm 560 00:29:59,831 --> 00:30:03,201 watching the rate change. 561 00:30:03,201 --> 00:30:05,904 Right away you know the rate changes 562 00:30:05,904 --> 00:30:12,210 as the cisplatin concentration changes, it's not zeroth order. 563 00:30:12,210 --> 00:30:14,279 And the second thing you know is, 564 00:30:14,279 --> 00:30:19,117 if you take any two of those and you take ratios, 565 00:30:19,117 --> 00:30:23,087 then the ratios are the same so it must be first order. 566 00:30:23,087 --> 00:30:26,357 That's one way to know what order you have. 567 00:30:26,357 --> 00:30:27,992 All right. 568 00:30:27,992 --> 00:30:28,493 Yeah. 569 00:30:28,493 --> 00:30:30,328 So if I have data. 570 00:30:30,328 --> 00:30:36,601 With data like that, with data you could do this. 571 00:30:36,601 --> 00:30:44,642 You could take ratios at two different times. 572 00:30:48,913 --> 00:30:53,351 And what does that get, it gets you the order. 573 00:30:53,351 --> 00:30:56,287 From that you can get the order and we'll see another example. 574 00:30:56,287 --> 00:30:57,789 And then, you can go further than 575 00:30:57,789 --> 00:31:01,960 that because then I could plug in data from one of the times, 576 00:31:01,960 --> 00:31:04,295 right. 577 00:31:04,295 --> 00:31:08,299 Once I know the order I could use data from one time, 578 00:31:08,299 --> 00:31:14,539 from one time to get k. 579 00:31:14,539 --> 00:31:16,841 Because once I know the order, I know 580 00:31:16,841 --> 00:31:19,611 how to write down the rate law, and then I 581 00:31:19,611 --> 00:31:21,613 can use any of these lines to get k. 582 00:31:24,949 --> 00:31:28,786 So we want to be comfortable with reactions, 583 00:31:28,786 --> 00:31:33,591 with rates going back and forth between order, rate law, 584 00:31:33,591 --> 00:31:34,826 integrated rate law, plots. 585 00:31:39,998 --> 00:31:45,169 So if I had data that looked like this I could do the same. 586 00:31:45,169 --> 00:31:48,806 Here's another reaction, I could say what order is it? 587 00:31:48,806 --> 00:31:50,508 I'm not going to do it, I'll just say it. 588 00:31:50,508 --> 00:31:53,378 So you take any two times and concentrations 589 00:31:53,378 --> 00:31:55,580 and what you have is that the ratio 590 00:31:55,580 --> 00:32:00,451 squared gives you the ratio of the rates, that means it must 591 00:32:00,451 --> 00:32:01,753 be a second order reaction. 592 00:32:01,753 --> 00:32:04,188 It means it must be, right. 593 00:32:04,188 --> 00:32:08,059 I had something that went into products 594 00:32:08,059 --> 00:32:11,396 and the dependence of the rate from this data, 595 00:32:11,396 --> 00:32:15,099 the dependence of the rate is that something's concentration 596 00:32:15,099 --> 00:32:17,101 squared and you can see it from the data. 597 00:32:19,771 --> 00:32:24,709 So well, let's see. 598 00:32:24,709 --> 00:32:29,180 I'm going back to the middle here. 599 00:32:29,180 --> 00:32:36,621 OK, so now, we just went to second order. 600 00:32:40,758 --> 00:32:47,999 So for second order what do you have? 601 00:32:47,999 --> 00:32:55,340 Well, you have that minus d of something, some reactant, 602 00:32:55,340 --> 00:32:57,775 and I just got one reactant here, 603 00:32:57,775 --> 00:33:00,478 if you think about it as A. So the same thing A 604 00:33:00,478 --> 00:33:03,681 went to something, OK, so minus the change in concentration 605 00:33:03,681 --> 00:33:08,319 of that with time is dependent on k times the concentration 606 00:33:08,319 --> 00:33:09,921 of that squared. 607 00:33:09,921 --> 00:33:16,194 And if we integrate this one, integrate then what do you get, 608 00:33:16,194 --> 00:33:19,564 you get 1 over the concentration of the something 609 00:33:19,564 --> 00:33:24,869 equals 1 over its initial value plus kt. 610 00:33:28,339 --> 00:33:29,040 You can see that. 611 00:33:29,040 --> 00:33:31,509 Take the t over here and take this over there 612 00:33:31,509 --> 00:33:35,246 and then that's going to be the integrated rate law. 613 00:33:35,246 --> 00:33:38,016 So now, look at that. 614 00:33:38,016 --> 00:33:40,218 What do I plot to get linear? 615 00:33:40,218 --> 00:33:44,255 I got get to linear, I don't like curves in reaction rate 616 00:33:44,255 --> 00:33:48,226 plots, I like linear lines because the linear line 617 00:33:48,226 --> 00:33:53,765 will tell me something about the reaction order. 618 00:33:53,765 --> 00:33:56,200 And by the way, the slope could tell me something 619 00:33:56,200 --> 00:33:57,602 about the rate constant. 620 00:33:57,602 --> 00:33:58,736 Right? 621 00:33:58,736 --> 00:34:01,439 And so if it's second order, the plot 622 00:34:01,439 --> 00:34:02,907 that gives you a linear line is 1 623 00:34:02,907 --> 00:34:05,610 over concentration versus time. 624 00:34:05,610 --> 00:34:06,210 So let's look. 625 00:34:06,210 --> 00:34:09,112 So let's say I had this data and I try to plot it. 626 00:34:09,112 --> 00:34:12,183 Well, the first thing I do is I say, well OK hold on, 627 00:34:12,183 --> 00:34:16,154 if I plot the concentration versus time that's 628 00:34:16,154 --> 00:34:17,522 what it looks like, not linear. 629 00:34:20,558 --> 00:34:22,994 That means it's not zeroth order. 630 00:34:22,994 --> 00:34:24,462 OK, I'm going to take the same data 631 00:34:24,462 --> 00:34:28,800 and I'm going to plot the Ln of it versus time, not linear. 632 00:34:28,800 --> 00:34:32,437 Not first order, but if I plot 1 over that concentration 633 00:34:32,437 --> 00:34:35,639 versus time it gives me a perfect linear fit, 634 00:34:35,639 --> 00:34:37,942 so it must be second order. 635 00:34:37,942 --> 00:34:41,045 Plots, order, linear. 636 00:34:41,045 --> 00:34:43,648 OK? 637 00:34:43,648 --> 00:34:46,551 We're not going to go beyond zeroth, first, 638 00:34:46,551 --> 00:34:48,052 and second order because what I want 639 00:34:48,052 --> 00:34:51,755 is for you to feel your oneness with reaction rates 640 00:34:51,755 --> 00:34:56,094 and kinetics through these three orders, zeroth, 1, and 2, 641 00:34:56,094 --> 00:35:00,765 and through these different concepts that are up there. 642 00:35:00,765 --> 00:35:07,405 So one more thing you can do, before I turn to temperature, 643 00:35:07,405 --> 00:35:11,109 one more thing you can do once you know the rate law is you 644 00:35:11,109 --> 00:35:15,379 can calculate how long it takes for the concentration 645 00:35:15,379 --> 00:35:18,783 to be cut in half. 646 00:35:18,783 --> 00:35:24,922 If I know the rate law, then I can calculate 647 00:35:24,922 --> 00:35:27,258 the half life, that's called. 648 00:35:27,258 --> 00:35:37,902 All right, so for example, if it's first order 649 00:35:37,902 --> 00:35:44,308 let's suppose it's first order then the integrated rate law-- 650 00:35:44,308 --> 00:35:46,911 I'm just going to put the two concentrations on the same side 651 00:35:46,911 --> 00:35:47,945 here-- 652 00:35:47,945 --> 00:35:50,081 A over A0. 653 00:35:50,081 --> 00:35:51,482 OK. 654 00:35:51,482 --> 00:35:54,385 So the integrated rate law gives me this. 655 00:35:54,385 --> 00:35:57,622 It's just what I had before somewhere. 656 00:35:57,622 --> 00:36:02,727 OK, but you can see, well what if the concentration of A 657 00:36:02,727 --> 00:36:05,062 is exactly 1/2 of the beginning concentration. 658 00:36:05,062 --> 00:36:13,337 So when A equals 1/2 the initial concentration, 659 00:36:13,337 --> 00:36:16,707 but then this becomes a 1/2. 660 00:36:16,707 --> 00:36:17,575 Right? 661 00:36:17,575 --> 00:36:22,914 So if I want to know how much time it takes to get to 1/2, 662 00:36:22,914 --> 00:36:25,049 that's a good thing to know just in general. 663 00:36:25,049 --> 00:36:28,953 How long do I have until half of this is left? 664 00:36:28,953 --> 00:36:32,757 Well, then you know that this is going to give you ln2. 665 00:36:32,757 --> 00:36:40,498 When A equals 1/2 A0 then ln2 equals kt. 666 00:36:40,498 --> 00:36:43,434 And we're going to call that an important. 667 00:36:43,434 --> 00:36:46,671 It's not just any time, it's called the half life, 668 00:36:46,671 --> 00:36:48,039 it's the time that it took to get 669 00:36:48,039 --> 00:36:52,510 to A being 1/2 of the initial. 670 00:36:52,510 --> 00:36:54,145 So I've got it. 671 00:36:54,145 --> 00:36:55,646 I've got it, I've got the half life. 672 00:36:55,646 --> 00:36:58,482 The half life is a very powerful tool. 673 00:36:58,482 --> 00:37:00,484 A number of you may have heard of carbon dating. 674 00:37:00,484 --> 00:37:04,055 This is just a picture of wild animals, 675 00:37:04,055 --> 00:37:05,957 but what happens, those wild animals 676 00:37:05,957 --> 00:37:10,394 breath in oxygen and other stuff from the air including stuff 677 00:37:10,394 --> 00:37:13,064 that contains a spread of carbon atoms 678 00:37:13,064 --> 00:37:16,334 and we know carbon has isotopes. 679 00:37:16,334 --> 00:37:17,902 We know about carbons isotopes, we've 680 00:37:17,902 --> 00:37:21,505 already talked about them, c12, c13, c14. 681 00:37:21,505 --> 00:37:25,376 C14 has this wonderful thing about it 682 00:37:25,376 --> 00:37:26,777 that it radioactivity decays. 683 00:37:29,447 --> 00:37:32,483 And it turns out that there's a certain concentration of that 684 00:37:32,483 --> 00:37:33,951 in the atmosphere at any given time 685 00:37:33,951 --> 00:37:37,488 and we can go back in history and know how much concentration 686 00:37:37,488 --> 00:37:39,757 there was in the atmosphere. 687 00:37:39,757 --> 00:37:43,961 And we know if these animals are breathing it in. 688 00:37:43,961 --> 00:37:49,634 We know that they should have that concentration at A0, 689 00:37:49,634 --> 00:37:51,902 except this isn't a concentration this 690 00:37:51,902 --> 00:37:53,104 is a number of atoms. 691 00:37:53,104 --> 00:37:56,474 But It's OK, it's still a first order process. 692 00:37:56,474 --> 00:38:00,711 The radioactive decay of c14 is a first order process. 693 00:38:00,711 --> 00:38:04,715 And so, because of that we can date, 694 00:38:04,715 --> 00:38:07,985 we can date things using carbon dating very accurately. 695 00:38:07,985 --> 00:38:12,323 This is a really awesome tool that relies simply on the half 696 00:38:12,323 --> 00:38:15,960 life, on knowing the half life. 697 00:38:15,960 --> 00:38:21,098 All right, here's a summary that I thought would be useful. 698 00:38:21,098 --> 00:38:21,699 This is it. 699 00:38:21,699 --> 00:38:23,734 This is everything we just talked about before we 700 00:38:23,734 --> 00:38:24,869 switch to temperature. 701 00:38:24,869 --> 00:38:27,471 Rate law, zeroth order, first order. 702 00:38:27,471 --> 00:38:29,740 And you're all like, why did I write this all down, 703 00:38:29,740 --> 00:38:30,741 it's all on this page. 704 00:38:30,741 --> 00:38:31,776 No, it's good to-- 705 00:38:31,776 --> 00:38:34,445 Did somebody say, yeah. 706 00:38:34,445 --> 00:38:36,881 It's good to write down, it helps you think about things. 707 00:38:36,881 --> 00:38:38,316 So here it all is. 708 00:38:38,316 --> 00:38:42,620 There is the zeroth order, first order, second order, OK? 709 00:38:42,620 --> 00:38:45,956 Integrated rate law that comes from that. 710 00:38:45,956 --> 00:38:48,459 The units of the rate constant. 711 00:38:48,459 --> 00:38:52,296 The linear plot to determine the rate constant. 712 00:38:52,296 --> 00:38:55,132 What gives you what the slope of that line is 713 00:38:55,132 --> 00:38:57,401 and then what the half life would be if you just follow 714 00:38:57,401 --> 00:38:59,170 this for the other two orders. 715 00:38:59,170 --> 00:39:01,672 OK so this is all that we just talked about 716 00:39:01,672 --> 00:39:04,208 and the best way to feel your oneness with this 717 00:39:04,208 --> 00:39:08,779 is to do some practice problems more than what we've just done. 718 00:39:08,779 --> 00:39:12,450 The next-- really? 719 00:39:12,450 --> 00:39:16,454 The next topic, I'm not going to spend the same amount of time 720 00:39:16,454 --> 00:39:18,689 on temperature and catalysts obviously, 721 00:39:18,689 --> 00:39:22,960 but I want to mention how these impacts reaction rates. 722 00:39:22,960 --> 00:39:28,099 We're talking about how fast the concentrations change. 723 00:39:28,099 --> 00:39:30,267 And to do that, what we're going to do 724 00:39:30,267 --> 00:39:34,438 is we're going to use the collision theory of reactions. 725 00:39:34,438 --> 00:39:37,208 And I've just written it down here what it is. 726 00:39:37,208 --> 00:39:39,043 What is the collision theory of reactions? 727 00:39:39,043 --> 00:39:42,279 What it is, is it says that they occur when particles collide. 728 00:39:42,279 --> 00:39:47,118 Why does a plus b go to c? 729 00:39:47,118 --> 00:39:49,553 Well, because things collided into each other and they 730 00:39:49,553 --> 00:39:53,491 got close enough or they maybe had the right orientation 731 00:39:53,491 --> 00:39:57,661 so that new bonds could form or others could break. 732 00:39:57,661 --> 00:40:00,164 And the theory also says that not all collisions result 733 00:40:00,164 --> 00:40:01,899 in the formation of product and that there 734 00:40:01,899 --> 00:40:05,002 are two factors that matter, the energy of the collision, 735 00:40:05,002 --> 00:40:06,737 and the orientation of the particles. 736 00:40:06,737 --> 00:40:08,439 I want to highlight those two factors. 737 00:40:08,439 --> 00:40:09,673 So energy of the collision. 738 00:40:09,673 --> 00:40:13,577 We're going to start with the energy of the collision 739 00:40:13,577 --> 00:40:15,379 and we're going to talk about that in terms 740 00:40:15,379 --> 00:40:16,580 of where you get that energy. 741 00:40:16,580 --> 00:40:18,215 You get it from heat. 742 00:40:18,215 --> 00:40:20,851 You get it from thermal energy, which 743 00:40:20,851 --> 00:40:24,155 means these things are vibrating and moving, 744 00:40:24,155 --> 00:40:26,090 maybe if it's a gas, they're bouncing off 745 00:40:26,090 --> 00:40:30,361 the walls of the container, that's temperature. 746 00:40:30,361 --> 00:40:31,829 How does that matter? 747 00:40:31,829 --> 00:40:33,731 Well, in order to understand how that matters, 748 00:40:33,731 --> 00:40:39,370 we have to understand, we have to think about this-- 749 00:40:39,370 --> 00:40:41,338 and this is what collision theory for reactions 750 00:40:41,338 --> 00:40:45,509 tells us to do is to think about a reaction in terms 751 00:40:45,509 --> 00:40:49,647 of an energy landscape and an energy barrier 752 00:40:49,647 --> 00:40:52,950 that you have to overcome. 753 00:40:52,950 --> 00:40:58,689 So here I have this Ea, which is the energy 754 00:40:58,689 --> 00:40:59,924 that it's going to take. 755 00:40:59,924 --> 00:41:05,062 I need to put that energy in for the collision 756 00:41:05,062 --> 00:41:05,996 to be strong enough. 757 00:41:05,996 --> 00:41:08,466 Think about it as like, well I just kind of didn't collide, 758 00:41:08,466 --> 00:41:12,503 I had a very low energy, so I'm below Ea 759 00:41:12,503 --> 00:41:15,306 and I can't get over this hill. 760 00:41:15,306 --> 00:41:17,875 It really is if you think about it like pushing a car, 761 00:41:17,875 --> 00:41:21,712 did I push it hard enough so it can go over the hill, 762 00:41:21,712 --> 00:41:24,448 or is it just pushed a little bit, that's 763 00:41:24,448 --> 00:41:27,718 the kinetic energy we're talking about, 764 00:41:27,718 --> 00:41:28,986 could it get over that hill. 765 00:41:28,986 --> 00:41:32,423 Because what we're seeing is that for this reaction 766 00:41:32,423 --> 00:41:34,859 to happen there's some amount of energy that's needed, 767 00:41:34,859 --> 00:41:38,896 that's the activation energy, that's the activation energy. 768 00:41:38,896 --> 00:41:40,297 OK. 769 00:41:40,297 --> 00:41:41,899 So what does that mean? 770 00:41:41,899 --> 00:41:44,101 Well, first of all, you should all 771 00:41:44,101 --> 00:41:45,636 be feeling something right now. 772 00:41:48,305 --> 00:41:51,675 And you know what I'm talking about, I'm talking 773 00:41:51,675 --> 00:41:54,879 about Svante, Svante Arrhenius. 774 00:41:54,879 --> 00:41:56,113 Right, somebody said it. 775 00:41:56,113 --> 00:41:57,548 You were feeling it. 776 00:41:57,548 --> 00:42:02,152 Why, because I'm talking about a process that has a barrier that 777 00:42:02,152 --> 00:42:06,423 is thermally activated, a process that has a barrier that 778 00:42:06,423 --> 00:42:07,091 is thermally-- 779 00:42:07,091 --> 00:42:12,062 Svante Arrhenius, crickets. 780 00:42:12,062 --> 00:42:17,434 Crickets and then intrinsic carriers. 781 00:42:17,434 --> 00:42:22,907 Activated processes, reactions, right, they have a barrier. 782 00:42:22,907 --> 00:42:24,475 They have barrier. 783 00:42:24,475 --> 00:42:27,912 Now here's the thing though, Ea is typically 784 00:42:27,912 --> 00:42:36,253 like maybe an electron volt, and we know that KbT is 0.025 eV. 785 00:42:36,253 --> 00:42:39,723 We've talked about this before and how is that possible. 786 00:42:39,723 --> 00:42:45,362 It's the same as what we talked about before because this 787 00:42:45,362 --> 00:42:46,497 is an average energy. 788 00:42:46,497 --> 00:42:48,666 If you put the Boltzmann constant in to room 789 00:42:48,666 --> 00:42:54,038 temperature, This is at room temperature-- 790 00:42:54,038 --> 00:42:57,775 If you put the Boltzmann constant in at room temperature 791 00:42:57,775 --> 00:43:00,411 you're going to get that small energy, 792 00:43:00,411 --> 00:43:03,380 but we know that thermal energy is a distribution. 793 00:43:03,380 --> 00:43:06,984 This is something we've talked about, so here it is again. 794 00:43:06,984 --> 00:43:08,619 So this is the Boltzmann distribution 795 00:43:08,619 --> 00:43:10,955 is what this distribution is called. 796 00:43:10,955 --> 00:43:13,490 And if I have my energy for activating 797 00:43:13,490 --> 00:43:17,361 a reaction, my barrier for the reaction to happen, 798 00:43:17,361 --> 00:43:18,929 shown there with the vertical line, 799 00:43:18,929 --> 00:43:22,032 it means that I have two temperatures. 800 00:43:22,032 --> 00:43:25,836 So yeah, kt may be small, but there's some tails 801 00:43:25,836 --> 00:43:29,406 out there where there is enough thermal energy, 802 00:43:29,406 --> 00:43:31,942 there's enough kinetic energy for this collision 803 00:43:31,942 --> 00:43:32,943 to lead to the reaction. 804 00:43:36,013 --> 00:43:39,683 So those tails grow larger and larger, 805 00:43:39,683 --> 00:43:42,786 the amount of molecules that have enough energy 806 00:43:42,786 --> 00:43:45,389 grows larger as you increase the temperature. 807 00:43:45,389 --> 00:43:48,025 That is Arrhenius. 808 00:43:48,025 --> 00:43:52,596 The probability for this to happen grows, that is 809 00:43:52,596 --> 00:43:54,331 what Arrhenius gives us. 810 00:43:54,331 --> 00:43:55,366 And so here it is mapped. 811 00:43:55,366 --> 00:43:59,903 This is something that is in the textbook that 812 00:43:59,903 --> 00:44:02,306 is a nice diagram because it maps the two together. 813 00:44:02,306 --> 00:44:04,341 You've got the reactant going to the products, 814 00:44:04,341 --> 00:44:07,478 there's an activated complex, it needs that activation energy 815 00:44:07,478 --> 00:44:11,315 and over there we've turned on the side these kinetic energy 816 00:44:11,315 --> 00:44:13,183 distribution plots. 817 00:44:13,183 --> 00:44:14,952 So you can see, when do I have enough? 818 00:44:14,952 --> 00:44:16,720 Well, when I'm over that activation energy 819 00:44:16,720 --> 00:44:19,556 and there is going to be some fraction of molecules 820 00:44:19,556 --> 00:44:23,560 that have enough and that fraction depends on temperature 821 00:44:23,560 --> 00:44:24,628 and that is Arrhenius. 822 00:44:24,628 --> 00:44:29,099 And so what we get is that the rate, the rate k, 823 00:44:29,099 --> 00:44:35,806 k the rate is equal to some constant A 824 00:44:35,806 --> 00:44:41,178 times e to the minus Ea over KbT. 825 00:44:41,178 --> 00:44:47,818 And remember, we use Kb for one collision, 826 00:44:47,818 --> 00:44:51,922 for a molecule or an atom. 827 00:44:51,922 --> 00:44:59,563 We would use R or r for a mole. 828 00:44:59,563 --> 00:45:04,435 Here I'm talking about a single event, one molecule colliding 829 00:45:04,435 --> 00:45:07,538 with another to make the reaction happen. 830 00:45:07,538 --> 00:45:10,874 Now, this is called the frequency factor 831 00:45:10,874 --> 00:45:12,776 and it's a constant. 832 00:45:12,776 --> 00:45:17,147 Constant, constant, and that's something 833 00:45:17,147 --> 00:45:22,453 that you could understand how this might depend 834 00:45:22,453 --> 00:45:25,889 on a combination of things. 835 00:45:25,889 --> 00:45:29,760 But it's assumed, incorrectly, but it's 836 00:45:29,760 --> 00:45:31,762 a good enough approximation for us, 837 00:45:31,762 --> 00:45:33,897 but it's assumed to be independent of temperature 838 00:45:33,897 --> 00:45:36,266 so we pull it out and call it a frequency factor. 839 00:45:36,266 --> 00:45:41,605 And it has in it information about whether these things 840 00:45:41,605 --> 00:45:44,475 really made the right collision or not, that's 841 00:45:44,475 --> 00:45:45,743 what A has in it. 842 00:45:45,743 --> 00:45:49,379 This exponent, Arrhenius is telling us 843 00:45:49,379 --> 00:45:53,717 this exponent tells me about that fraction, that fraction, 844 00:45:53,717 --> 00:45:55,352 but A tells me about orientation. 845 00:45:55,352 --> 00:45:57,121 So here's an example. 846 00:45:57,121 --> 00:46:02,159 Here's N0 plus 03, and on the top line you can see the N0-- 847 00:46:02,159 --> 00:46:04,962 right so, the O's are red and N is blue-- 848 00:46:04,962 --> 00:46:07,498 and the N0 is coming in, but it's coming in either way 849 00:46:07,498 --> 00:46:09,399 whether it's N or whether it's 0, 850 00:46:09,399 --> 00:46:12,136 it's coming into the wrong oxygen. 851 00:46:12,136 --> 00:46:14,171 It's hitting that wrong oxygen and so 852 00:46:14,171 --> 00:46:16,340 it doesn't do anything because the one in the middle 853 00:46:16,340 --> 00:46:19,643 isn't going to be very reactive, not 854 00:46:19,643 --> 00:46:20,878 at least at this temperature. 855 00:46:20,878 --> 00:46:23,547 But then you've got a different case 856 00:46:23,547 --> 00:46:25,549 where it comes in a little differently, 857 00:46:25,549 --> 00:46:28,051 and in fact, the nitrogen is what's 858 00:46:28,051 --> 00:46:31,655 coming in and leading the way to that oxygen on the end 859 00:46:31,655 --> 00:46:34,491 and that leads to the reaction. 860 00:46:34,491 --> 00:46:38,195 So you can imagine now it's not just how fast they're moving, 861 00:46:38,195 --> 00:46:45,068 which is what the exponent tells us, it's more complicated. 862 00:46:45,068 --> 00:46:45,836 Right? 863 00:46:45,836 --> 00:46:47,471 And this is called the frequency factor 864 00:46:47,471 --> 00:46:50,440 because it's all these complicated effects rolled 865 00:46:50,440 --> 00:46:54,111 into the frequency of the collision being right, 866 00:46:54,111 --> 00:46:57,915 not just the temperature. 867 00:46:57,915 --> 00:46:59,016 OK. 868 00:46:59,016 --> 00:47:02,052 And so this gives us the temperature dependence 869 00:47:02,052 --> 00:47:04,755 of the rate constant, this gives us 870 00:47:04,755 --> 00:47:06,957 the temperature and dependence of the rate constant, 871 00:47:06,957 --> 00:47:08,625 which is very important. 872 00:47:08,625 --> 00:47:11,829 This is not time, this is temperature. 873 00:47:11,829 --> 00:47:12,329 All right? 874 00:47:12,329 --> 00:47:14,264 This is a different thing than everything else 875 00:47:14,264 --> 00:47:17,167 we talked about here, which involved time dependence, 876 00:47:17,167 --> 00:47:21,205 that's temperature dependent. 877 00:47:21,205 --> 00:47:24,474 And finally, the last thing and just to show you this 878 00:47:24,474 --> 00:47:29,079 is my very last point, is that just like before, 879 00:47:29,079 --> 00:47:34,318 if I wanted to run a reaction and make it go faster, one way, 880 00:47:34,318 --> 00:47:37,321 just like with semiconductors is to increase the temperature, 881 00:47:37,321 --> 00:47:40,624 but I don't want to run my phone at 600 Kelvin. 882 00:47:40,624 --> 00:47:43,927 So what do we do, we use chemistry. 883 00:47:43,927 --> 00:47:47,164 I may have reactions that I want to run a lot faster. 884 00:47:47,164 --> 00:47:50,601 In fact, I very often do, and what do I do, 885 00:47:50,601 --> 00:47:54,438 I use chemistry and those are called catalysts. 886 00:47:54,438 --> 00:47:57,007 What a catalyst does, and this picture shows it 887 00:47:57,007 --> 00:47:59,710 in the context of collision theory, 888 00:47:59,710 --> 00:48:01,979 I've got these barriers I'm trying to get over, 889 00:48:01,979 --> 00:48:03,513 here it's flipped, it doesn't matter. 890 00:48:03,513 --> 00:48:05,415 There's a barrier here, so the reactant 891 00:48:05,415 --> 00:48:06,917 is higher than the product, it's OK, 892 00:48:06,917 --> 00:48:10,587 there's still a barrier that I have to overcome. 893 00:48:10,587 --> 00:48:14,558 What a catalyst does is without being consumed, 894 00:48:14,558 --> 00:48:17,961 what a catalyst does is it's another material in there where 895 00:48:17,961 --> 00:48:22,165 it allows that reaction to happen with a lower barrier. 896 00:48:22,165 --> 00:48:24,368 That's what a catalyst is and you better 897 00:48:24,368 --> 00:48:25,636 believe this is important. 898 00:48:25,636 --> 00:48:28,138 So a catalyst lowers that without changing 899 00:48:28,138 --> 00:48:30,274 the temperature. 900 00:48:30,274 --> 00:48:33,577 And in just 20 seconds, here's my why this matters. 901 00:48:33,577 --> 00:48:36,847 Catalytic converters is one of the most important technologies 902 00:48:36,847 --> 00:48:40,417 for pollution that has been invented in over the last 50 903 00:48:40,417 --> 00:48:41,351 years. 904 00:48:41,351 --> 00:48:45,188 It's changed the game in terms of what comes out of that car. 905 00:48:45,188 --> 00:48:46,323 Why does it work? 906 00:48:46,323 --> 00:48:47,958 It wouldn't work, you wouldn't get rid 907 00:48:47,958 --> 00:48:50,727 of these things, these toxic things, 908 00:48:50,727 --> 00:48:52,663 you wouldn't get rid of them unless you ran it 909 00:48:52,663 --> 00:48:55,832 at 1,000 degrees and you're not doing that underneath your car 910 00:48:55,832 --> 00:48:58,068 next to the gas tank. 911 00:48:58,068 --> 00:49:00,470 But if you put the right catalyst in, 912 00:49:00,470 --> 00:49:03,607 all of those reactions to get rid of those toxic chemicals 913 00:49:03,607 --> 00:49:06,176 can happen much more quickly and efficiently. 914 00:49:06,176 --> 00:49:07,444 Right? 915 00:49:07,444 --> 00:49:08,178 OK. 916 00:49:08,178 --> 00:49:09,546 Have a great weekend. 917 00:49:09,546 --> 00:49:10,414 See you guys on Monday.