 Okay. So let's start the evening off with one of these gas law problems. This one says, how many moles of hydrogen gas occupy 0.500 liters at standard temperature pressure, or STP? So in order to do this problem, you've got to remember what standard temperature pressure is. Remember standard pressure, does anybody remember what that is? We have 1.008, and we'll say, just because this has 3 sig paves, we'll put 3 sig paves here, okay? And temperature? 273. Yeah, it's going to be 273 Kelvin, or 0 Celsius. So let's just say 0 Celsius, and then we'll add that 273 to it, because we have to get this in Kelvin, if you recall. And I'm sure you do, and that's why we said that. Okay? So notice, what did we notice about this problem? When it said, when it was talking, it said that these are the values that we have, what is the moles? It didn't say anything is changing, right? Does everybody agree with what I'm saying? Yeah. Okay, so since that's the case, we're just going to use the regular old gas law. And it says we're going to solve for the number of moles I'm recording. So that's why I put a question mark there, okay? So we're going to have to rearrange this equation to solve for n. That's what we're really saying. So let's go ahead and do that. So how do we do that? We've got to divide both sides by what? RT. Very good. Okay, so when we do that, we're going to cancel R there, cancel T there. And what do we get? We get n equals kB divided by RT, like that. So in order to do this problem, right, we have P, we have T, R. Where does that come from? Constant. The ideal gas constant, I have to give that to you. 0.0821 liters ATM per mole kelvin, okay? So if you'll forget what pressure units or what temperature units or what volume units, do I have these things in? You can just go back and look at this constant. It'll tell you volume units have to be in liters. Pressure units have to be in AT units. Number has to be in moles. So everybody okay with what I'm saying? So now it's just really a plug-and-check problem. Okay, so the pressure is 1.00 ATM. The volume is 0.5 liters, 0.500. We're going to divide that by R. This is kind of the shorthand way of writing it. To where this stuff is actually underneath that. Okay, so you can see what I'm doing. So it can really cancel out the units here. 0.0821 liters ATM divided by 1 mole kelvin. And then the temperature, of course, is 273 kelvin. So hopefully now, I think this is easier way to see how we cancel out our units. So let's go ahead and cancel out. We've got ATM on the top, ATM on the bottom. So we cancel that out. Leaders on the top, leaders on the bottom. And then we go down to the denominator. And we see at the top of the denominator we have kelvin. At the bottom of the denominator we have kelvin. So those cancel out. So for 1 divided by 1 divided by moles, that's going to make moles our units of this. Okay, so let's just write out our units real quick. So moles. And that's what we're looking for, right? 0.0821 divided by 273. And the number of moles that I get, I'll put this into scientific notation. So three significant figures. It's going to be 2.23 times 10 to the negative 1,2 moles of H2. So that's how many moles of hydrogen gas are in 0.5 liters of volume. Okay? Are there any questions about this one? Or can we kill it? We good? Okay.