 Okay, let's try this problem. It's a little more difficult, I guess. It says a 1.00 liter flask contains nitrogen gas at 25 degrees Celsius and 1.00 atm pressure. What is the final pressure in the flask? If an additional 2.00 grams of nitrogen gas is added to the flask and then the flask is cooled to negative 55 degrees Celsius. Okay, so let's just write over here, so N2 is going to be N1 plus 2.00 grams just to remind ourselves. Okay, and we'll put T2 over here at negative 55 degrees Celsius as well. Okay, so if we don't do that we'll forget about it. We'll forget what we're doing. Okay? Or at least I won't. Okay, so the first part of the problem really is asking you to figure out what is the number of bowls of nitrogen gas that you have. Okay, so in order to do that you've got to use your ideal gas law. P equals nRT. Okay, so Pv equals nRT. Right, and we know R that's given to us. 0.0821 liter atm whole. So we have this, this, this, and this. Well, this isn't in the right units, right? So plus 273, that's going to be 298 Kelvin. Now that's in the right units, in the right units, in the right units, right? So let's rearrange our equation n equals Pv divided by RT. Is that right? Okay, wonderful. So now we can plug in all of these numbers. Okay, so pressure 1.00 atm, volume 1.00 liter divided by R, 0.0821 liter atm per one mole Kelvin at 298 Kelvin. Okay? So cancel, cancel, cancel, cancel, cancel, cancel. So what do we get? So 1 divided by 0.0821 and then divide that by 298. So the number of moles that we get, is anybody else doing this on the calculator as well? You're just following along. That's all right. The number of moles we get are going to be 4.036, 4.09 times 10 to the negative 2 moles. Okay? Okay, so that's how many moles of nitrogen gas we had to begin with, okay? Can I erase all of this business here and just I'm going to leave this, okay? I'm going to leave that. I know I'm going a little fast here. Okay, so we're going to call that n1. Okay, so look over here. We've got to figure out, well, what is n1 or n2? And we know n1, right? And this is 2 grams, but that's not moles, right? So we're going to have to convert that to moles, okay? So let's do that first. Well, what do we know about n2 gas? Well, nitrogen itself is 1401 amu, so n2, the molar mass, will be 28.02 grams per mole. That makes sense, okay? So 2 grams, well, we should be able to figure out how many moles 2 grams is, right? Okay, so let's figure out what is the number of moles in 2 grams. So 2.00 grams times at the bottom here, 28.02 grams, one mole. Cancel, cancel. So that's how you do. Remember when you were asking me that question earlier? That's how you do it, not how you were trying to do it, okay? So 2, so 2 divided by 28.02 and we get 3.13 times 10 to the negative 2 moles, like that, okay? So that's that right there, so n2 is going to equal n1, 4.09 times 10 to the negative 2 moles, plus 7.13 times 10 to the negative 2 moles. So the total number of moles now is 0.112 moles of n2, okay? Does that make sense? Was that done? Because we're adding 2 grams to that glass, okay? But not only did we add more gas to it, we cooled it down, okay? So this temperature, remember it's no longer 298 Kelvin, but it's negative 55, right? So let's store this one. Okay, so negative 55 plus 273, right? It's going to give us 218 Kelvin. Notice it didn't tell us that we changed the volume of the flask, nor did we change the pressure, okay? So we're going to do pb equals nRT again, except now we're not going to use that one, we're not going to use that one, but we're going to use, sorry, and we're not going to use this one, right? We're going to use those things over there, okay? So what are we looking for? I can't even remember anymore. It says the final pressure, okay? So, right? Okay, so let's do it, pb equals nRT. So p equals nRT divided by 0.112 moles, R821 liter ATM per one mole like that, temperature 218 Kelvin divided by volume, cancel, cancel, cancel, and we get pressure, okay? 15 divided by one. So what's the new pressure that I get is 2.0118. Well, that is simple, but when I look at this, you just got to be very logical with the steps, you know? You got to do it, okay? What do I know here? And then figure that out. And then from there, you got to think, okay, what does it tell me now, you know? And then come over here and do this and then it's just pb equals nRT once and then pb equals nRT again, you know? So you're doing it one way first and then kind of a little bit backwards the other way. Remember I told you that at the beginning? Yeah, okay. Does that make sense? Okay, yeah, sure, just watch it. Any other questions before we kill it? Okay.