 Okay, wonderful. So let's try this one now. How many grams of B2H6 will react with 3 moles of O2? So the equation is already balanced. You can tell by the coefficients being in places and so not. I'll tell you that you need to balance the equation if you need to balance. If it's already balanced, I won't say you need to balance. Or if it's already balanced, I won't say. Anyways, notice there's a 1 to 3 to 1 to 3 ratio of these products and reactants. But we're looking for just BH2 and O2. So we know there's a 1 to 3 ratio of those two things. So how many grams of B2H6 will react with 3 moles of O2? So first thing you want to write down is the number of moles of O2 is 3.0 of 3.9 of the moles of O2. So now we've got to figure out, well, what's the number of moles of B2H6? So in order to do that, we have to use this number and that ratio we were talking about, the 3 to 1 ratio. 3.00 moles O2 times... Well, we're going to put moles of O2 at the bottom because we want to cancel that out. So for every 3 moles of O2, there's 1 mole to cancel out moles of O2 like that. We will have, of course, the moles of B2H6. That's all we've got left over. So 3 times 1 divided by 3, that's going to be 1.00 moles of B2H6. Now we've got moles of B2H6. Unfortunately, that's for grams. Or fortunately, because we could take moles and convert it to grams using the molecular way. First thing we've got to do though is figure out, well, what's the molecular way of B2H6? So we've got two B's in it. B is going to be 10.81 grams per mole and H, we have six of them. So 1.008 grams per mole. Now we just multiply those numbers and add them together. So we get 2 times 10. And for my molecular way, I've got 27. All we've got to do is figure out the mass of B2H6. So in order to get rid of moles of B2H6, we've got to put moles of B2H6 down here. So for every one mole of B2H6 we have, it's going to be 27.67 grams. Cancel, 1 times 27.67, of course that equals 27.67 grams of B2H6.