Chemical Reactions (10 of 11) Stoichiometry: Moles to Moles - OK, this video is another in the series of everybody's favorite chemistry topic-- stoichiometry. In this case, we're going to call this moles to moles because we're going to be given moles of one of the substances in the chemical equation. And we want to figure out how many moles do we need to react that number of moles and how many moles we're going to produce of each of the products. OK, so let's look at the chemical equation. Here we have it/ it's nitrogen gas plus fluorine gas equals NF3. So you can see, we have been given 5.65 moles of F2. And we want to know how many moles of N2 and how many moles of NF3 we're going to produce in this reaction. OK, now we need to remember that any chemical equation shows us a molar or particle relationship. So one mole N2 plus 3 moles of F2 will yield 2 moles of NF3. And we're going to remember that that's a molar relationship and not a gram relationship or a mass relationship. OK, now for this problem and any other stoichiometry problem, you should keep in mind the three steps for successful stoichiometry. Step one is convert from grams to moles. Now we've been given moles, so we don't need to do step one, OK? Step two is use the molar ratio to determine moles of the other substances. OK, we're going to use step two. And then the third step, in general, is to convert from moles back to grams. But we have not been asked to figure out how many grams. We have only been asked to figure out how many moles. So we're only going to use step two in this problem. We were given moles. We want our answers in moles. So we're just going to use the molar ratio. OK, now the way we start this is we're going to write down the number of moles and the chemical formula for the substance that we've been given. So you should always write down these three things-- the number, the unit, and the chemical formula. That will help you to stay more organized. I know it seems like a little bit of extra writing, but don't complain. It'll help you out, I think, in the end. OK, now we want to get out of moles of NF2, so that means we have to put moles of F2-- excuse me. We want to get out of moles of F2 we have to put moles of F2 in the bottom. That will allow us to cancel. We want our answer to be in moles N2 because we're going to solve for moles of N2 first. So therefore, we're going to put the moles of N2 on the top. Now we're going to use our molar ratio. This is 3 to 1. So we put a 3-- that's what this coefficient tells us. There's a 3 here, and there's a 1 here. So we're going to put the 3 down here, the 1 up here, and that's our molar ratio. And now we can cancel. And you can see now we're left with moles of N2. And you can see that if we want to react 5.65 moles of F2, we are going to need 1.88 moles of N2. So that is the number of moles that we're going to need. And we're not going to convert to grams because we're not asked to do that in this problem. All right, let's figure out the number of moles of NF3. So now you can see, once again, we're going to start with the number of moles of the substance that we have been given. So I'm using that value again-- 5.65 moles of F2. We're going to make our little T-chart, so we can convert. I call railroad tracks. Then we're going to put the moles of F2 in the bottom again. We're going to put the moles of NF3 on the top. We're going to look at our molar ratio. You can see, it's 3 to 2. So the 3 goes on the bottom. The 2 goes on the top. We cancel our molar units. We cancel our molar units. And we are left with moles of NF3. So now you can see, that in order to react 5.65 moles of F2, we're going to need 1.88 moles of N2. And we're going to produce 3.77 moles of NF3. OK, that's all there is to it. We figured out we were given moles. We figured out how many moles we're going to use of N2 and how many moles of NF3 we're going to produce. And that is all there is to it. OK, that was only step two in the successful stoichiometry steps of which there are three. OK, so thanks for watching. I hope that was helpful. If you thought that was helpful, please give me a thumbs-up in the comments section below. And we will see you next time.