 Okay, so let's do one more of these gas law problems. This one, hopefully, you can tell is a Gay-Lusach problem. It reads, a steel container of nitrous oxide at 15.08 Tm is cooled from 25 degrees Celsius to negative 40 degrees Celsius. What is the final pressure of the system at constant volume? So, can anyone tell if this is going to be a problem where things are changing or things are staying the same? They're changing. They're changing, right? Okay, so when we do that, what do we do? We say PV equals nRT of ones below everything but the R's divided by PV equals nRT, putting two's below, okay? So what two things, two variables are changing, right? Pressure and temperature, right, does everybody see that? So pressure, we don't cancel out, right, because they're different values. Volume's the same, it even says constant volume, so that's going to cancel. Number of moles didn't change, cancel that out, and R, that's the gas constant, it changes, okay? So our new equation is P1 divided by P2 equals T1 divided by T2, okay? So we need to solve for P2, right? So P2 is here, let's isolate that variable, okay? So the first thing we're going to do is do what? Flip both sides, okay? So when we do that, we say P2 divided by P1 equals T2 divided by T1. Is everybody okay with what we've done so far? Okay, so remember we're trying to isolate P2, so what do we need to do next? Multiply. Multiply by what? P1. P1, right? So if we multiply by P1, what happens here? Cancel. Cancel, cancel, and multiply here by P1, like that, okay? So let's just write the final equation up here. So P2 equals T2 times P1 divided by T1, like that. So again, if you're having trouble with your algebra, you're going to have trouble with these problems, okay? So make sure you attempt a number of these problems before you come for the axioms, okay? So I'm going to erase this stuff down here, and then we'll just plug and chug. Well, I guess we have to do one more thing before we start plugging in numbers. What are we going to have to do? Convert Celsius to Kelvin. Convert Celsius to Kelvin because we have to have our temperature in Kelvin units. So how do we do that? Add 273. So what do we get? 298 Kelvin there. Add 273 there. And we get 233 Kelvin. Okay. So now it's plug and chug. So P2 equals T2, which is 233 Kelvin. Times T1, 15.0, 18. Divide it by T1, which is 298 Kelvin, like that. So hopefully you guys see that Kelvin's are going to be canceled out, leaving us with units of 18, right? Pressure units of 18 are good units, so we've probably done the right thing. Let's do this together. So 233 times 15, and then divide that by 298. And this is going to be, of course, three significant digits. So I get 11.718. So that's going to be the pressure of your nitrous oxide. Okay. Are there any questions on this one? Wonderful.