1 00:00:16,400 --> 00:00:17,568 Why does this matter? 2 00:00:17,668 --> 00:00:20,537 Why does counting and thinking about how much of stuff 3 00:00:20,637 --> 00:00:24,742 you're using by using chemistry and moles? 4 00:00:24,842 --> 00:00:25,609 Why does that matter? 5 00:00:25,709 --> 00:00:28,345 Well, let's take an example. 6 00:00:28,445 --> 00:00:31,815 Let's take an example of nothing less than the number 7 00:00:31,915 --> 00:00:34,418 of humans on this planet. 8 00:00:34,518 --> 00:00:36,887 This is the population of humans. 9 00:00:36,987 --> 00:00:42,026 And you can see that it wasn't all that much until lately. 10 00:00:42,126 --> 00:00:44,528 But let's focus in on this part here. 11 00:00:44,628 --> 00:00:45,963 Let's focus in on that part there. 12 00:00:46,063 --> 00:00:46,797 Right. 13 00:00:46,897 --> 00:00:47,965 So that's billions of people. 14 00:00:48,065 --> 00:00:51,201 So if I zoom in on this, there's a change. 15 00:00:51,301 --> 00:00:52,136 Look at that. 16 00:00:52,236 --> 00:00:53,470 It's kind of going a little bit up. 17 00:00:53,570 --> 00:00:55,439 But now, it really kicks up. 18 00:00:55,539 --> 00:00:58,375 What happened during that time? 19 00:00:58,475 --> 00:01:03,814 What happened is a very important chemical reaction, 20 00:01:03,914 --> 00:01:08,018 became easy to do or a lot easier. 21 00:01:08,118 --> 00:01:09,486 OK? 22 00:01:09,586 --> 00:01:11,255 And the process that enabled that 23 00:01:11,355 --> 00:01:15,059 is called the Haber-Bosch process. 24 00:01:15,159 --> 00:01:19,596 But it is what allowed us to feed billions 25 00:01:19,696 --> 00:01:23,300 of people in a sustainable way. 26 00:01:23,400 --> 00:01:25,502 It's arguable whether we're doing that sustainably 27 00:01:25,602 --> 00:01:28,005 but in a way where we could actually produce enough-- 28 00:01:28,105 --> 00:01:29,173 enough what? 29 00:01:29,273 --> 00:01:30,507 Enough ammonia. 30 00:01:30,607 --> 00:01:36,146 And here's the deal you see, because plants need nitrogen 31 00:01:36,246 --> 00:01:38,148 to grow. 32 00:01:38,247 --> 00:01:39,650 Right? 33 00:01:39,750 --> 00:01:42,485 And there's 70% of the atmosphere is nitrogen. 34 00:01:42,586 --> 00:01:45,322 But it's useless, because it's N2. 35 00:01:45,422 --> 00:01:47,890 And N2 is one of the strongest bonds in nature. 36 00:01:47,991 --> 00:01:49,926 And plants can't break it. 37 00:01:50,027 --> 00:01:52,930 Now, we knew how to break it before. 38 00:01:53,030 --> 00:01:55,899 We knew how to do this before, right? 39 00:01:55,999 --> 00:01:57,835 This is called fixing-- 40 00:01:57,935 --> 00:02:05,042 fixing nitrogen. And the way it works is you go N2 plus h. 41 00:02:05,142 --> 00:02:09,213 This is a reaction, goes to NH3. 42 00:02:09,312 --> 00:02:10,547 What is wrong with this? 43 00:02:10,646 --> 00:02:11,548 [inaudible] 44 00:02:11,648 --> 00:02:14,184 It's not balanced. 45 00:02:14,284 --> 00:02:15,419 Thank you. 46 00:02:15,519 --> 00:02:20,257 Did anybody say, balancing is the same as mole ratio. 47 00:02:20,357 --> 00:02:23,927 Balancing and mole ratio's the same-- counting. 48 00:02:24,027 --> 00:02:25,129 Remember, we talk about that. 49 00:02:25,228 --> 00:02:26,829 But balancing is counting. 50 00:02:26,930 --> 00:02:28,565 So let's see-- oh, 2 here. 51 00:02:28,665 --> 00:02:31,602 OK, that helps me with the nitrogen. 52 00:02:31,702 --> 00:02:32,836 Oh, but this is H2. 53 00:02:32,936 --> 00:02:34,438 I meant to put that in the first place. 54 00:02:34,538 --> 00:02:36,874 And then so this is a 3. 55 00:02:36,974 --> 00:02:38,841 That reaction was known and doable. 56 00:02:38,976 --> 00:02:41,978 But it took tremendous amounts of energy. 57 00:02:42,079 --> 00:02:43,313 So it's very difficult to scale. 58 00:02:43,413 --> 00:02:46,316 And Haber-Bosch came up with a way using catalysis 59 00:02:46,416 --> 00:02:47,784 to do it at much lower temperatures. 60 00:02:47,885 --> 00:02:50,187 Catalysis is something we'll learn later in the semester. 61 00:02:53,055 --> 00:02:55,125 But how do we answer this question? 62 00:02:55,225 --> 00:02:56,192 What's my question? 63 00:02:56,293 --> 00:02:59,129 My question is how long can we keep going? 64 00:02:59,228 --> 00:03:03,767 50% of every protein you put in your body-- 65 00:03:03,867 --> 00:03:06,503 50% come from this-- 66 00:03:06,603 --> 00:03:09,706 comes from some plant that was grown using this process. 67 00:03:09,806 --> 00:03:11,842 That's how important it is. 68 00:03:11,942 --> 00:03:15,846 It's 500 million tons of nitrogen 69 00:03:15,946 --> 00:03:18,515 is made this way every year. 70 00:03:18,615 --> 00:03:20,484 Well, it's just counting. 71 00:03:20,584 --> 00:03:27,724 One mole of ammonia is 17 grams. 72 00:03:27,824 --> 00:03:29,226 Oh, we're doing the same thing. 73 00:03:29,326 --> 00:03:30,194 How did I know that? 74 00:03:30,294 --> 00:03:31,728 Periodic table. 75 00:03:31,828 --> 00:03:33,697 That's how I knew that. 76 00:03:33,797 --> 00:03:36,733 One mole-- if that many molecules of ammonia, 77 00:03:36,833 --> 00:03:38,067 I've got 17 grams of it. 78 00:03:44,007 --> 00:03:48,078 Let's say I just need to make the same amount of-- 79 00:03:48,178 --> 00:03:52,216 it says so times 10 to the 6 tons. 80 00:03:52,316 --> 00:03:59,256 I need that much tons of NH3 per year. 81 00:03:59,356 --> 00:04:00,724 That's our-- yeah, per year-- 82 00:04:00,824 --> 00:04:01,858 per year. 83 00:04:01,959 --> 00:04:04,861 OK, so that sets up my problem. 84 00:04:04,962 --> 00:04:06,930 I know how much I need. 85 00:04:07,030 --> 00:04:11,301 I know how many atoms we're talking about in one mole. 86 00:04:11,401 --> 00:04:15,505 Now, I can actually understand how many moles-- 87 00:04:15,606 --> 00:04:18,207 so I'm just going to not do the detailed math 88 00:04:18,308 --> 00:04:19,543 but how many moles I have. 89 00:04:19,643 --> 00:04:24,848 So I've got 30 times 10 to the 12th moles. 90 00:04:24,948 --> 00:04:33,457 This is how many moles I needed per year. 91 00:04:33,557 --> 00:04:35,726 How much do I have? 92 00:04:35,826 --> 00:04:37,261 Well, we know how much the atmosphere 93 00:04:37,361 --> 00:04:38,762 weighs-- it turns out. 94 00:04:38,862 --> 00:04:42,799 We know how much the atmosphere weighs. 95 00:04:42,899 --> 00:04:50,574 The mass of the atmosphere is something like 5 times 10 96 00:04:50,674 --> 00:04:52,876 to the 21st grams. 97 00:04:52,976 --> 00:05:05,355 And if I take 78% of that as my N2, so 78% is N2, 98 00:05:05,455 --> 00:05:09,293 then I can tell you that I've got-- 99 00:05:09,393 --> 00:05:20,070 let's see, 1.4 times 10 to the 20th moles of N2. 100 00:05:20,170 --> 00:05:21,705 That's how much I have available. 101 00:05:25,809 --> 00:05:26,943 OK? 102 00:05:27,044 --> 00:05:29,279 So if I keep on taking N2 out of the atmosphere, 103 00:05:29,379 --> 00:05:31,882 then I can now answer the question just like the candle. 104 00:05:31,982 --> 00:05:33,216 All right, how long do you have? 105 00:05:33,317 --> 00:05:35,052 I can answer the question, how long can we 106 00:05:35,152 --> 00:05:39,890 keep taking N2 out of the atmosphere 107 00:05:39,990 --> 00:05:43,493 and using Haber-Bosch, right? 108 00:05:43,593 --> 00:05:45,662 Oh, well, you would use the balanced reaction. 109 00:05:45,762 --> 00:05:47,197 So for every mole event do I take, 110 00:05:47,297 --> 00:05:49,032 I get two moles of ammonia. 111 00:05:49,132 --> 00:05:49,933 That's good. 112 00:05:50,033 --> 00:05:51,835 And you can work backwards. 113 00:05:51,935 --> 00:05:54,438 And you can learn that you're good. 114 00:05:54,538 --> 00:05:58,608 We're good for now. 115 00:05:58,709 --> 00:06:00,711 We have roughly 100 million years. 116 00:06:03,747 --> 00:06:04,147 OK? 117 00:06:09,586 --> 00:06:12,389 We have 100 million years that we could keep consuming. 118 00:06:12,489 --> 00:06:15,325 And then we'll run out of N2 in the atmosphere. 119 00:06:15,425 --> 00:06:17,094 How fun was that? 120 00:06:17,194 --> 00:06:19,129 OK, I love doing this. 121 00:06:19,229 --> 00:06:21,832 Now, when I get excited-- 122 00:06:21,932 --> 00:06:23,133 wow. 123 00:06:23,233 --> 00:06:26,336 Wait, before I get excited, what's the limiting reagent? 124 00:06:26,436 --> 00:06:27,771 [? add ?] enough N2. 125 00:06:27,871 --> 00:06:29,005 Is it N2? 126 00:06:29,106 --> 00:06:30,841 How do you know? 127 00:06:30,941 --> 00:06:31,641 How could you show? 128 00:06:31,742 --> 00:06:34,344 How can you prove? 129 00:06:34,444 --> 00:06:36,646 Limiting range, it means what runs out first? 130 00:06:36,747 --> 00:06:40,050 Well, oh, I'll just take H2 from the atmosphere, right? 131 00:06:40,150 --> 00:06:42,185 Na, uh. 132 00:06:42,284 --> 00:06:44,488 There's no H2 in the atmosphere. 133 00:06:44,588 --> 00:06:46,256 Where's the H2? 134 00:06:46,356 --> 00:06:48,625 Di da, it's over here-- 135 00:06:48,725 --> 00:06:49,726 H2O. 136 00:06:49,826 --> 00:06:50,894 It's in the oceans. 137 00:06:50,994 --> 00:06:52,295 How much H2O do I have? 138 00:06:52,396 --> 00:06:52,796 Well-- 139 00:06:52,896 --> 00:06:55,832 [laughter] 140 00:06:55,932 --> 00:06:58,268 It turns out you've got a lot. 141 00:06:58,368 --> 00:07:02,639 10 to the 23rd-ish moles of H2O, right? 142 00:07:02,739 --> 00:07:04,307 10 to the 23rd-ish moles. 143 00:07:04,408 --> 00:07:07,277 And so because of those coefficients of the reaction, 144 00:07:07,377 --> 00:07:09,913 you know exactly which one is going to run out first. 145 00:07:10,013 --> 00:07:12,749 You know it's N2, so your answer over there was correct. 146 00:07:12,849 --> 00:07:14,951 N2 is the limiting-- 147 00:07:15,051 --> 00:07:16,019 I love that little dance. 148 00:07:16,119 --> 00:07:17,454 I'm going to try to learn that. 149 00:07:17,554 --> 00:07:20,123 I'm going to learn that later. 150 00:07:20,223 --> 00:07:22,426 If you try this, you go 100 million years. 151 00:07:22,526 --> 00:07:25,762 You run out of N2-- plenty of H2 left.