[SOUND] So I already told you how energy is recombining atomic or nuclear bonds into a more stable state, but those are just words. Today I want to really show you what that means and also show you how to figure out just how much energy you get. So, let's say I have a molecule. So the key thing in a chemical reaction is that the atoms don't go away, they just get combined into different patterns. A methane molecule, a carbon with four hydrogens, can go and get put together into two waters and a carbon dioxide. All of the molecules are different. The atoms, the constituents of the molecules are the same. Let me give you another example. Here we have a shot of alcohol. Now, this undoubtedly is ethyl alcohol, something you could drink, but about the same volume as one mol of methyl alcohol. If I take it and set it on fire, combust it, combine it with oxygen, I can also make molecules better in a more stable state. So let's take that reaction and try to get some numbers. To do that, we have to have units. The typical standard unit, SI unit for energy is a joule. But in chemistry, we tend to use something called a calorie. Now, a calorie is the amount of energy that it takes to take one gram of water and raise it 1 degree centigrade. Not a whole lot of energy. Let's not confuse this with the other typical use of calorie while we try to determine how much energy is in food. Here is a Big Mac and it has 650 Calories, but not those kind of calories, right? Not these calories. This is a Calorie with a capital C, it really stands for a thousand calories, a Kcal. So, 1,000 calories is equal to one kilocalorie, which is equal to one food Calorie with a capital C. The Big Mac has 650 or you can have a whole pound of fat, a pound of butter, and that's about 2,500 food calories, and I told you that the SI unit of energy was joules, they way it works is that 1 of these calories is 4.1868 Joules, and this will eventually give us our comparison to other types of energy units that we need. So, how much energy can we get from this reaction? This is methanol, the shot glass of methyl alcohol. We're going to add oxygen to it, and it's going to turn into carbon dioxide and water vapor. Now we have to make a balanced chemical reaction. Remember, the individual Hs or Cs don't disappear, they just get rearranged into more stable states. So we got one carbon on each side, that's good. We go four hydrogens. So it looks like we're going to need two water molecules, and oxygens, I've got three up here. Hey, and lookie there. I got one, two, three, four here. So we're going to need an extra. This is going to be plus another half of an oxygen. Well, that's one oxygen, three, four, one, two, three, four, good, balanced equation. Very important, you have to start with a balanced equation. Now what we're doing when I first put that match on that methanol, I like thinking about this as a well. All right? So a methanol molecule, the carbon atoms, and the three hydrogens, and the oxygen, and the other hydrogen take some amount of energy to release them, to break up their bonds. That amount of energy is 48.1 Kilo calories per mole. We do everything in Avogadro's numbers of atoms -48.1, why negative, because it's bound, it's below 0. I have to put some energy in, I have to light it on fire to break it up and what do we break it up and put it back into? Well, I'm going to put it into a carbon dioxide and a carbon dioxide is more tightly bound. The well is bigger. It's -94.1 and I'm going to have two water molecules, and each of them is also tightly bound at -57. How do I know those numbers? Well you can get a chart like this. This is called entropy and it tells you how tightly bound a certain molecule is, and you can see here that we can go to the methanol -48.1, we can go to water as a gas it's -57.8, and we can go to the carbon dioxide over here on the left at -94.1. This is the CO2, this are each of the waters. Now you might wonder, where's oxygen? Why isn't oxygen on this chart? Why didn't I make a well for my oxygen here? Well you see, all these numbers are relative to something and we put them relative to the oxygen level because most chemical reactions involve burning, which means combining with oxygen, and when we do that, we can just assume that oxygen is at zero. Now that make some math much easier. So, now I have this picture of the wells. But we need to figure out how much energy we get. Well, the nice thing is once we have these numbers all we need to do is write an equation. All right, we have -48.1, that's what we start with and that's going to equal -94.1-57.8-57.8, and then something I'm going to call Q. That is the amount of energy released. It's that energy. It's the rearrangement of chemical bonds into a more stable state. Carbon dioxide, water vapor are more stable than methanol. If I now solve this, it's just math, add these numbers together, add them to this side. The answer is 161.6 kcal = Q. Burning that shot glass of ethanol gives you a 161 food calories. You might be thinking in your mind hey, wait a minute. I thought I remembered if I drank a shot of alcohol, don't drink methanol, okay, it was ethanol. If I drink it's 100 calories, 100 kilocalories, right? Well remember, the stuff you drink isn't 100% pure, right? This would be for 200 proof. So, half that, yeah you got about the right number. This is how much energy you'd get from a chemical reaction. That's what you need to know about chemistry. [MUSIC]
