Okay so now I'm going to do a whole bunch of mole ratio problems a whole bunch so you can really get a handle on these they're super important for stoichiometry for understanding stoichiometry okay each problem I'm going to do it two ways first I'm going to treat the equation the chemical equation kind of like kind of like a recipe all right where we've got our ingredients and then we've got the step we're baking this method really makes sense like you'll understand what you're doing but it requires a little bit of thumb then I'll solve each probably using a conversion factor method the conversion factor method doesn't require any thought but it doesn't make any sense so it's really easy to get in the habit of only using the conversion factors running through the math but having absolutely no idea what you're actually doing or why you're doing it okay so that's why I'm going to do each of these problems two different ways okay so let's get started here is the first equation I'm going to be working with two moles of h2o water makes two moles of hydrogen gas and oxygen here if there's no coefficient in front of the oxygen in front of one of these chemicals we know that it's really one that it means one mole so hey if it helps you go ahead and write that one there's our equation here is the question how many moles of o2 of oxygen will be produced from six point two moles of water okay so first of all I want you to think of this like a recipe and right now it's saying that we start with two moles of this and that gives us two moles of this and one mole of this but we're not talking about starting with two moles of h2o we're talking about starting with 6.2 moles of h2o okay so this is just like when you're cooking and you've got a double or triple or quadruple a recipe what do we have to do to this recipe so that instead of starting with two moles of water we start with six point two moles of water okay we have to multiply everything in this equation by something that's going to get us 6.2 moles of water we can figure this out a couple lists first thing I can do is I can do 6.2 which is this divided by two which is that and that gives me 3.1 okay that like gives me the factor and what I mean by that is that we take each one of these numbers and we multiply it times three point one two times three point one and now we get six point two moles of this okay so now we're starting with six point two instead of two we multiply this by its 3.1 now we'll also want to multiply the number of H two times three point one so now we're getting six point two moles of H 2 and we want to take this number which is one times three point one multiply it there and we get three point one moles of o2 so once again we treat this like a recipe in the kitchen and we're doubling or tripling instead of multiplying by two or by three or by 4 we multiply everything in this recipe by 3.1 we get six point two here so that's what we're starting with then we get six point two moles of h2 and we get three point one moles of o2 and that kind of makes sense right because there's this two to one ratio of water to oxygen we start with two of these we get one of these so this is half of what we have here okay so if we start with six point two we multiply everything by three point one and we get six point two here and this three point one is half of what we had over here okay so that's how we can do this equation treating it like a recipe in the kitchen now let's look at how we can do this using conversion factors okay what we're going to do is we're going to start with six point two moles of h2o now what I want to do is I want to write a conversion factor that tells me the relationship between the moles of water and the moles of oxygen okay we can sum it up with this it tells us for wherever two moles of h2o I get one mole of o2 two here one here okay we get this relationship and what I can do is I can use this to write a conversion factor there are two different conversion factors I can get from this I can write two moles of h2o over one mole of o2 okay that's one or I can flip it I can do one mole of o2 over two moles of it so of course I'm just getting the numbers from the chemical equation two and one so I've got these two conversion factors that are flips I could use either one of them they're both equally good the one that I want to choose though is the one that I can multiply by this and cancel out moles of h2o okay that's going to be the one that has h2o on the bottom because it's on the top over here so I'm not gonna use this one I am going to use this one I'm going to multiply it here and now I have h2o on the top h2o on the bottom so they cancel out and when I do this math I'm going to do six point two times one divided by two equals three point one moles of o2 and check it out I use a conversion factor method and I get the exact same