 Okay, so this one's from the practice test. Balance the equation. How many grams of hydrogen sulfide are produced when 10 grams of gold sulfide are reacted? Okay, so the first thing we need to do is balance this equation. We look over here. We're going to balance in, then sulfur, and then gold. So first we say, well, we've got two hydrogens here, two hydrogens here. Those are balanced. We should have actually balanced sulfur first, sorry. So we've got three sulfurs here, and only one sulfur here, right? So we need to put three there. So sulfurs are now balanced. Now let's look at hydrogen. Well, we've got two times three, that's six over here, right? But we only have two over here, so we need to multiply that by three. So three times two is six. Three times two is six. Hydrogen balance, sulfur is balanced now. And gold, we have one over here and one over here. Oh, it is supposed to be two. Okay, so we've got two over here, one over there, two, okay? So now gold. So that's the first part of that problem. Now the second part asks, how many grams of H2S are produced when 10 grams of gold sulfide are reacted? Okay, well, so we have a mass of gold sulfide. So we're going to have to figure out the number of moles of gold sulfide. So number of moles of an AU2 and S3 multiplied by, well we know the molecular weight is 490.21, so 490.21 grams per one mole. Grams cancel out, up to, so that's the number of moles of Vista, but we're interested in the number of grams of Vista here. So we need to figure out first the number of moles of that, okay? So what's the number of moles of H2S? Well, we take the number of moles, multiply that by, for every one mole, two S3, there's three moles of H2S. So moles AU2S3 cancel. We'll just take that number and multiply that by 3.0612 moles of H2S. So the mass of H2S then would be, 1, 2, moles of H2S, 34.082, I got 2.046. It's the same four steps every time. We want to do the same four steps, okay?