 Okay, this video is going to be devoted to balancing sort of beginning practice of balancing chemical equations. So we're just going to do two short exercises to practice balancing. Here is our first equation. I will tell you immediately not balanced, although eventually you'll be able to look at them on your own and figure that out. If you are playing at home and you have a way of balancing that works for you, you are more than welcome to do it that way. However, I'm just going to show you the way that I would do it. Usually I make a table and on the table I have three columns left and right and then whatever atom I'm talking about. So L and R stand for left and right side of the arrow. So basically you sort of split the equation down the middle where the arrow is. So what I do is I just go atom by atom. In this case I would start with mg for magnesium and I ask the question how many magnesiums on the left side of the arrow. Well, let's put the numbers that are implied to be in front here just for clarity. There's one magnesium on the left. How many magnesiums on the right? Well, there's one magnesium as well. So magnesiums are balanced. Then I go to the next element, H. How many hydrogens on the left? There's one. How many hydrogens on the right? There are two because there's one implied here and this is H2 which means two Hs stuck to each other. So what you end up doing to figure out the amount of hydrogens or anything is you multiply the number in front of the formula times the subscript next to the atom. So this is going to be one times two. So two H atoms, two. Not balanced. Now a lot of times students want to go on to the other elements to try and see what's going on with each of the other elements. My recommendation is to not do that. Maybe this is a tip for how to live your life. I don't really know but my philosophy for balancing is fix your problem and worry about the other problems that might be lurking around the corner later. But if you can fix this problem easily, do it and then worry about the other stuff. So the left side is the side that does not have enough and so as I mentioned in the previous video, usually you try to fix the side that doesn't have enough. In other words, you try to boost this number. We have to turn it into a two because we have two on the right. The only numbers that we're allowed to change are the numbers in front of the formulas. So this is a one at the moment. If I want to turn this one into a two, I can change that one that was in front of the HCl. This is Hc lowercase l. I can change that to a two. And if I do that, now I have two hydrogens on the left as well. Let's fix that. So now let's go back. Magnesiums are still balanced. We didn't mess with them. Hydrogens, we have two on the left. We have two on the right. Those are balanced as well. Anything else that we need to balance? Oh yeah, the chlorine. That's a Cl there. How many chlorines on the left side? Some of you may say one because there's a one here. However, this two counts for the entire molecule. It doesn't just count for the H. It counts for the H and the Cl. So not only are there two H's, but there are now two chlorines. And you have to realize this. This is a common mistake that students make is that they forget that this number, whatever number they changed, it changes everything in the formula. So if there are two H's, we've already accounted for that. There are two chlorines. So we put a two there. How many chlorines are on the right? Well, there's a one in front of this molecule. And there's a two that's a subscript next to the chlorine. So we do one times two. There are two chlorines as well. So everybody's balanced. Magnesiums, we have one on the left, one on the right. Hydrogens, we have two on the left, two on the right. So the way this equation was written originally, mg plus HCl makes mgCl2 plus H2 not balanced. Or think of it as being a slightly incorrect recipe. And what we did is we said, yeah, there should be a one here. And there was. However, there should be a two over in front of the HCl. And the other ones that were implied to be HCl, we did a two over in front of the HCl. And the other ones that were implied to be there in front of the other formulas, they get to stay. So the correct formula is one magnesium needs to be mixed with two HCl's. And that will make two mg, I'm sorry, that will make one mgCl2 and one H2 molecule as well. So we just balanced another equation. Now you can ask yourself, why do we bother balancing equations like this? Mostly, all right, here's a moment of honesty. Mostly, it's to make you suffer. I remember talking with a chemist a few years ago, and we were talking about the state of chemistry education. And we were both saying it is kind of funny that beginning chemistry students are forced to balance equations, because real chemists probably have not had to balance equations in 150 years. So you are learning a very old technique. But again, this is a test of whether you can think logically about unusual things. So that's sort of what this is here for. In a more practical sense, however, why do we bother balancing equations? It's a more accurate description. It more clearly communicates what's happening in a chemical reaction. It also lets us figure out how much product, how much of a different product we can make when you see a chemical reaction. So in other words, imagine that you had a recipe book. But the amounts of the ingredients and the amount of servings you could make in your recipe book were all wrong. You would not be happy with that recipe book. You wouldn't know how many eggs you needed to buy, how many servings you could make if the recipes were all wrong. If you had a chemistry book where all of the equations were unbalanced, you would be similarly unhappy. So because you wouldn't know how much magnesium you would need to mix with how much HCl and how much H2 you could actually make or how much MgCl2. The only way that you could figure out how much of everything you could make and how much of everything you needed is if the equation was balanced. So that's the motivation behind why chemists actually balance equations when they do balance them. So as far as what you need to know, should be able to look at an equation and tell whether it's balanced or not. If it's not balanced, you should be able to balance it. And this requires a fair amount of practice. So here's some more practice. Here is an equation. The first question is, is it balanced? I'll tell you right off the bat, no. You can spend a couple of minutes balancing it. So you can pause the video, and when you unpause, I will go through it. So the way that I would do this, again, is I would make my table, left side and right side of the arrow, and a column for what type of atom we're talking about. And I just go one by one through each atom. So let's start with carbon. How many carbons on the left? Well, there's one, because let's write in the ones that we're starting with here. So there's no subscript to the right of the carbon. So there's a one that's implied, so it's 1 times 1. So 1 carbon on the left. How many carbons on the right? Well, there's no subscript to the right of this carbon either. So we're doing 1 times 1 on the right side as well. 1 carbon on the right. Carbons are balanced. Yay. Let's go to the next element. Next element is hydrogen. There's a 4 that's a subscript to the right of the hydrogen. So we do 1 times 4 is 4. There are four hydrogens on the left. There's a 2. There's a subscript of 2 to the right of this hydrogen. So we do 1 times 2. There are two hydrogens on the right, not balanced. And again, what you typically do is you find the side that does not have enough, and you try to boost up this number. So we need to turn this 2 into a 4 to make the H's balance. However, I don't get to change this number. I can't say that we have H4O. That's not allowed. The only number I get to change is this one, this one, this one, and this one. Obviously, this is the one we want to change because that will change the number of H's that we have. And if I change this from a 1 to a 2, in other words, if I double it, then it's 2 times 2, and we would have four hydrogens. So this 2 would be transformed into a 4. So now we have four H's on the left. Four. We have four H's on the right. Four. Now it's balanced. So are we done? Nope, we've got another element waiting in the wings. It's oxygen. How many oxygens on the left? There are two because of this subscript of 2 and this 1 in front. So 1 times 2 is 2. Two oxygens on the left. How many oxygens on the right? This can be tricky to some students. The problem is there are oxygens in two different formulas on the right side. And you have to make sure that you count them all. So how many oxygens here? Well, there's a subscript of 2 and there's a 1 here. So there are a total of two oxygens in this molecule. But that's not the only one that has oxygens in it. There's a 1 implied to be in the formula for water, for one oxygen. But we have two of them. So what's 2 times 1? That's 2. So there are two oxygens also that are in our two water molecules. So two water molecules have two oxygens in them. One CO2 molecule also has two oxygens in it. So if we count up all of the oxygens, all of them, on the right side of the arrow, it's a total of four oxygens. So the oxygens are not balanced either because we only had two oxygens on the left. We've got four on the right. So we need to boost the side that does not have enough. However, we are only allowed to change this number in front of the formula. So what number should we change it to? Well, if I double it, if I change the 1 to a 2, then 2 times 2 is 4. And so we have four oxygens now on the left. We have four oxygens on the right. So the correct equation was not CH4 plus O2 makes CO2 plus H2O. The correct formula is 1 CH4. You don't need to put the one there, but sometimes it helps for clarity. It has to be mixed with two O2s. That will make one CO2, and it will make two waters. And so now this is balanced. Now some of you may want a lot of practice doing this. If you Google this phrase, PHET, balancing chemical equations, and you look at the first hit that you get, there is a website, I guess, at the University of Colorado, where they have a pretty helpful game for helping you practice balance equations. So if you go to this site and you click on Game, you can pick easy equations to balance, moderately difficult, or more difficult equations to balance. And basically you just play along. So if we go to level 2, the only thing I don't like about the game is that it sets all of the numbers to 0 at the beginning, all of the numbers in front. You should really set them to 1. So if we set them all to 1, then it gives you this visual of the different atoms. And then you can adjust the numbers up and down to try to balance your equation. So this site can be pretty useful. I think a lot of students like it. If we have one of everything in our equation, if we look, there are two yellow ones on the left, there's only one yellow one on the right. So maybe if we double the amount of yellow ones on the right, that will be balanced. There are two orange atoms on the left. There are two orange atoms on the right. So those are balanced. There are two white atoms on the left. There are now two white atoms on the right. So we've probably balanced it. The correct balanced equation is 1.0f2 plus 1.h2o is transformed into 102 plus 2.hf. And then we can check to see if we're right. And that was a very loud ding that's hurting my head now. But we got it right. And then you can go along and continue to play. So if you find that site useful, knock yourself out. That is the end of practicing balancing equations.