[SOUND] So throughout this course, we're going to be talking about energy, environment and everyday stuff. When you talk about energy you need to be quantitative. It doesn't do you any good if we only talk about, this is how energy's made. But rather we want to put some numbers with it, we want to be able to compare. To do that, we'll need units, I live in America. I think we're the only country that still uses the British system. Even the British decided to use the metric system. As a scientist, I love the metric system. But I still have to relate to the every day stuff that's in this country of 320 million people. So the English unit for energy is the British Thermal Unit, the BTU. The amount of energy it takes to raise 1 pound of water, 1 degree Fahrenheit. How much more usable and even used in the US unit, is the calorie? A calorie is the amount of heat it takes to raise 1 gram of water, 1 degree centigrade. Now, that is a metric unit. When people talk about food and they say, how many calories are in food? They actually are talking about kilocalories, 1,000 calories. A McDonald's Big Mac sandwich has 530 calories, food calories. If you actually converted that to of course, kilocalories, it's the same, 530 kilocalories. If we wanted the small c calorie, the calories that's actually the 1 gram of water per degree centigrade, it would be 530,000. There is another energy unit, ion metric energy unit, called the Joule. And that's the standard energy in it. A Joule, relates to a calorie by the conversion of 1 calorie is 4.1868 Joules. Many times you will have things related in number of jewels, sometimes you'll have calories, sometimes you'll have quads. A quad is a quadrillion British thermal units, BTUs, 10 to the 15th BTUs. Sorry for all this. When we get to nuclear systems I've gotta tell you even one more energy unit. And that's the electron volt. The electron volt is a very useful unit when you're dealing with single atoms and single electrons. Turns out if you take one charged particle and take it through the potential difference of 1 volt, it gains one EV of energy. 1.6 times 10 to the minus 19 J is 1 eV. Let's calculate how much energy you get from a reaction. When I told you about the definition of energy, my definition of energy, it's putting bonds into a more stable state. How do you know if something's more stable or less stable? Sometimes you just know. Nitroglycerine, not very stable. A seashell, pretty stable. But we can put numbers on it. If we look at a chart of the heat of formation, the enthalpy of formation, this tells us how stable something is. If it's below zero, it's stable. And the more negative it's, the deeper it is into a well, the harder it would be to get out of the well. Think about it, you're stuck in a well, and the well is about this far, you just step out. I'm out. You're in a well that goes down for 100 meters, well, that's pretty tough to get out of. It's the same thing for a stable molecule. So if we want to see how much energy we get out from something, we need to take it into a more stable state. We need to rearrange the atoms. Let's take the example of methanol, burning methyl alcohol. It's the most simple of alcohols. It's a carbon, it's got three hydrogens, and then to make it an alcohol, an O, an oxygen, and another Hydrogen. Methanol burns very completely, it even has an invisible flame, that's because all you are making is carbon dioxide in water vapor. So if we start with the methanol molecule itself, you can look up on a chart and see that it has a particular heat of formation. In the units of kilocalories per mole, and a mole is a certain number of atoms. Turns out for methyl alcohol, it's about a shot glass full. That number of atoms has a heat of formation of -48 kilocalories per mole. We're going to start with that. That we're going to burn it. So we're going to mix it with oxygen, we'll combust it. And it turns out for this type of unit scale oxygen up to zero. So we get some oxygens, we rearrange the bonds, rearrange these bonds into water and CO2. And when we do that, we can all figure out what are the stability for water and CO2. Well, let's look at the chart. CO2 is at -94. It's more stable than methanol. Water is at -57. So if we want to figure out how much energy is released, we can do a simple equation, we take the -48, it equals -94, -57, -57, and plus some unknown, the amount of energy released. We usually use the letter q, and now we just have a very simple algebra equation. Stick it in your calculator, and you get q being 161 kilocalories per mole. Of course, a shot of alcohol, not this kind of alcohol, this one makes you blind, is something you can drink. You take a shot, and you might say, hey, how many calories in that? Well, ethyl alcohol has a few more calories than methyl alcohol. I think its number's around 200. You might say, wait a minute, I looked up vodka in my calorie counter, it says 100 calories. Well, that's because you're not drinking 200 proof, 100% alcohol when you take a shot of vodka. Your shot of vodka is 100 proof, or 80 proof. It's only 80%, not 80, it's only 80 out of 200, 40% alcohol, or 50% alcohol. The rest of it is war, which of course doesn't have any calories. It's an interesting thing about proof, the word sounds like you're trying to prove something, and indeed you are. 100 proof alcohol burns. So if you were selling someone some alcohol, and you diluted it with water, how would they know? Hey, this is under proof. Prove it. Set it on fire. It doesn't burn, it's not under proof.