Hi, I'm Robin Higgins and this is chemistry concepts and problems. Alright, so if you are looking for dozens of problems to give someone or to practice on, I would recommend looking at a very specific topic that you want to get better on and then Googling or Binging I guess some people do that, whatever you need to study specifically because there's hundreds and thousands of different chemistry concepts. In this video I'm going to go over one of the most crucial which is balancing reactions. Alright, so let's take a typical combustion reaction. So we're going to react our fuel. In this case it's methane and combustion reactions always happen with oxygen, gas or air and remember you can't just do it. You have to have a spark so we'll just put heat over here, triangle equals heat and it's going to make in this case carbon dioxide and water. Alright, so balancing just makes sure that we know how much of the reactants are required to react with the products and so we can see here that if we look a the number of oxygens, we have two on this side so two oxygens on the reactants, but on this side we have one, two and then three, so three oxygens on the products. This means that right now we are not balanced so we will be balanced when every different type of element, carbon, hydrogen and oxygen has the same number of that element on the left side as the right side. So what I like to do is start with the most rare element and in this case there's only one carbon on this side and one on this side so I'll start with carbon and like I just said, there's one here and then there's one here which means that for right now these chemicals are balanced completely fine. Okay, so next I'll go to hydrogen and we have four here and we have only two here. Now that means to make it equal we can't do anything to the four. We can't make that less so we are going to go ahead and put a big 2 here. So remember we can't change the subscripts. We can only change the coefficients. Now that I have two a coefficient of two here and I have a total of four hydrogens, I now have a total of two plus two, four oxygens on this side but I only have two here. So we're not balanced on oxygens yet but we will be if I go ahead and I add a 2 right here, now I have one carbon on each side, four hydrogens on each side and four oxygens on each side. So now we are balanced. Alright, so like I said before, this is a combustion reaction so it's very similar to what's happening in your car when you turn it on. You are reacting your fuel which isn't methane usually but some other type of hydrocarbon which means only hydrogens and carbons reacting with air and then this is the byproducts that your car creates. So there's lots of other chemistry concepts but balancing is definitely something that everyone has to master. I'm Robin Higgins and this is general chemistry problems and concepts.