 All right, the last video introduced you to how to read a chemical equation. Unfortunately there's a problem with our chemical equations. Some of you may have noticed it in the previous video, however I'll just point out that there's always got to be a problem, otherwise I wouldn't have a job. And we have to come up with a solution to the problem. The way that I'm going to introduce the problem is by telling you a story that is very similar to chemical equations. So let's say that I go home tonight and I say, honey, we're going to have a barbecue. I know at the moment that I'm recording this it is about minus five degrees Fahrenheit out, but let's pretend that I tell my wife we're going to have a barbecue and I say I got everything we need. I got two hamburger patties because screw the kids. I got two slices of bread. What are we going to do? We're going to heat them up and I'm going to make two sandwiches. Two hamburger patty sandwiches, one for you and one for me. And what does she say to me? Well, she says you're an idiot because you didn't get enough bread. How many slices of bread do we need? Well, if you're playing along at home, you should look at this and each sandwich. I know this is overkill. Needs two slices. And if I tell you, if I told her that I'm making two sandwiches, well, I need four slices and you only got two. So she sends me back to stop and shop. She says, get more slices of bread, idiot. So I come back now with four slices of bread and now my plan will work. I can take two patties, mix them with four slices of bread, heat them up and I can make two sandwiches. So what you say is the original setup that I had when it was two patties, two slices and two sandwiches, you would say my recipe was unbalanced. And when I fixed it by correcting the amount of bread that I needed, then you would say my recipe is now balanced. And this type of problem shows up in chemistry an awful lot. And the principle is essentially the same as what we just did here, although because you're more accustomed to thinking about food, this was probably very easy and you're not so accustomed to looking at chemical equations, balancing may at least initially be difficult for you. May not, but sometimes it is. So what we did here, I want you to think about what we did is, what we did is we had a recipe where the amounts of the ingredients and the amount of stuff that you can make was wrong. It was almost right, but this number in particular was wrong. And so we fixed it by changing our recipe to have the correct amount of ingredients and the correct amount of stuff that you could actually make. And that is what we are going to do with chemical equations. And this whole process that we're about to introduce is called balancing chemical equations. So this is an example that I showed you in a previous video and some of you may have noticed that it's not balanced. Here's the equation, here's the stuff that I started out with. One thing that I should point out is that if there is no number in front of the formula, the number one is implied, so right now there are ones implied to be in front of every formula. So what this equation is saying is, I took 1H2, I mixed it with 102, I heated it up and I made one water. However, if you draw this out in cartoon form, it's pretty easy to see what's wrong. This is one H2 molecule because each red circle is supposed to be one H, so this is an H2. This is one O2 molecule and inside of my one O2 molecule there are two oxygen atoms. But because they're connected, they're called one O2 molecule. And here's my one H2O molecule. And so if you look at this in cartoon fashion, you can see that the stuff on the left does not exactly match the stuff on the right. I've got two red circles here, two red atoms on the left. I've got two red atoms on the right. So nobody got lost, right? All the H's are accounted for. However, I've got two oxygen atoms on the left side and I've only got one on the right. There it is. So what this is telling you is that the equation is not balanced. Or for me, the easiest way to think about these equations is they are just like recipes. And something is wrong with our recipe. We mixed H2 with O2 and we got water, but somehow the amounts are not correct. So the way that you have to fix this is you're only allowed to change the numbers in front of the formulas. You can change this one, you can change this one, and you can change this one. You don't get to change the formulas themselves. You can only change the numbers in front. You can change any of them. You can change all of them. But we're going to have to change at least one of those numbers to make the amounts balance out. Because right now, we don't have enough not enough oxygen atoms on the right. Now I'm going to show you a couple of wrong ways of doing this, or considered to be wrong. And you'll see sort of why I'm trying to point this out. A lot of times I will show beginning students this equation and I'll say it's not balanced and they agree that it's not balanced. And I say please balance it. And they go, all right, I'm going to balance it. Now it's balanced. There are two hydrogens on the left, there are two hydrogens on the right, there are two oxygens on the left, there's one oxygen here, and I made a new one. So this must be the balanced equation. Technically speaking, this is balanced, but it breaks one of the rules about how to balance equations. So you also have to think of this a little bit as a game and there are rules that you have to follow. One of the rules, one of the most important rules is you don't get to add new materials. And that's what the person did when they balanced it this way. They said, not only did I make water, but I also made O. So the way to think about this is even though this equation is not balanced the way that it is, you have to assume that whoever wrote the equation down was competent enough to know that they only made water and that they only used H2 and they only used O2. They were not so horrible at chemistry that they forgot that they also made an O. So you don't get to balance the equation by adding new materials, not allowed. Even though technically they did balance the equation. The other way that is incorrect that students try to balance an equation, let me put the ones back in, is by doing this. I say, okay, it's not balanced, not enough oxygens, there's got to be two on the right. They say, alright, I'm going to balance it. Now it's balanced. This is also considered incorrect, even though technically it is balanced. The other rule is, you don't get to change the formula. In other words, the chemist is telling you, I took H2's, I mixed them with O2's, and I made water. I did not make H2O2, so you don't get to tell me what I made. You have to assume that whoever wrote this equation down was at least competent enough to know that they made water and they didn't make some other material. So you can't change the formulas. Again, the only numbers you're allowed to change are the numbers that are in front of the formulas. And the numbers that are in front of the formulas are just the amounts. So to reiterate, if you think about this as a recipe, we have a bad recipe. But the only thing that we get to change in our recipe is the amount of the ingredients, or the ingredients, and or the amount of the stuff that we made. So let's get to work and try to fix this. Right now it's not balanced. This side, not enough O-atoms. But I only get to change the amount, I only get to change this one. So the only way that I can fix it is by doubling the amount of waters. So if I change that one to a two, then the oxygens are balanced. I started with two oxygens, I ended with two oxygens. So we're good, right? You should all be screaming no, we're not good. We fixed one problem, we fixed the oxygen problem, but we made ourselves a new problem. We now have four H-atoms. On the right, we only have two H-atoms. On the left, so we unbalanced the H's. So we have to fix that too. And usually the easiest thing to do is to fix the side that does not have enough. So this time the left side, not enough H-atoms. But we only get to change the numbers in front of the formulas. So if I change this one to something else, I'm going to mess up the oxygens which are already balanced. We don't want to change that one. However, we don't have enough H-atoms on the left side. So why don't I double them? If I doubled the amount of H-2's, in other words, if I change this one to a two, then we can count how many H-atoms do we have on the left. We've got one, two, three, four. How many H-atoms do we have on the right? One, two, three, four. H is balance. How many O's do we have on the left? One, two, on the left. How many O's on the right? One, two. O's balance. There are no other elements there. There are no other types of atoms there. So we have written a correct recipe. Or more formally, we have written a balanced chemical equation. That is that two H-2's have to mix with one O-2, and that will make two waters. So another way to think about this is the original equation H-2 plus O-2 makes water. And remember, there are ones implied to be in front of everywhere. This is an incorrect recipe. It's almost correct, but the amounts are wrong. So if I went up to you and I said, look, I've got a recipe for making pancakes, but I gave you the wrong amounts of eggs and the wrong amounts of cups of flour and that type of thing, if you knew enough about how to make pancakes, you might be able to say, you're almost right. You need eggs. You need flour and all of that stuff. But the amounts that you have are incorrect. That's basically the situation that I set you up with, and that you come back and you do this little accounting trick, and you say it's not that one H-2 has to be mixed with one O-2 to make one water. It's that two H-2s have to be mixed with one O-2, and that will make two waters. The whole process that we just did is called balancing an equation. And we're going to do a fair amount of this in the coming videos. So here are the rules for balancing equations. You need the same number of each type of atom on the left and the right side of the arrow. And you can only change the amount or the number in front of each formula. You can change any of those numbers in front of each formula, but that's all you get to change. You can't change the type of material, and you can't add new materials in, and you can't subtract any of the materials that were already written out. So just to summarize, you're not allowed to put a 2 here, because if you did, you're telling people that they didn't make water, and you have to assume that they were at least talented enough to know that they actually did make water. So you only get to change the numbers in front of each formula. So those are the basics for balancing chemical equations. In the next video, you'll do some practice in balancing.