 So, let's go ahead and determine reaction spontaneity from enthalpy values. So we're going to have to calculate the change in entropy of the universe and decide whether this is going to be greater or less than zero. Okay, so in this problem it says that 298 Kelvin, the formation of ammonia, has a negative change in entropy of the system. Then it gives this equation and it also gives delta S, not this system, but degrees of the system. So, it is 197 joules per Kelvin. Calculate the delta S of the universe and state whether the reaction occurs spontaneously or not. So, delta S of the universe is going to be the delta S of the system plus the delta S of the surrounding. Okay, so how do we go about calculating the delta S of the surrounding? So, it's going to be the negative delta H of what? A system, very important, but it's the system divided by what? The temperature and what is that going to be in the universe? Kelvin. Okay, so is everybody okay with what we've done here? And remember, if this is greater than zero, then it's spontaneous. If it's less than zero, then it's non-spontaneous. Add this temperature, of course, okay? So, first thing we have to do now is figure out, well, what's the delta H of the system? So, we have the standard uniformation of ammonia. So, we're going to have to figure out what the actual enthalpy of this system is, okay? So, the change in H of the reaction, so that's going to be equivalent to the change in H of the system. And so, how do we do that? It's products minus reactants, right? Times the number of moles, okay? So, two, like that, and that's all of the products that we have. So, we're going to subtract that from all of the reactants, okay? This equation is already balanced. I guess I should have said that you have to have this equation balanced in order to do that. So, what do we have here? Well, we've got one mole of nitrogen, but I don't see nitrogen's heat of formation over here. What is nitrogen's heat of formation, guys? Zero. Zero, rad zero kilojoules per mole. And why is that? It's because it's at its standard state, and it's in its elemental form, okay? So, one mole times zero kilojoules per mole. And of course, you don't need to write all this stuff out. I'm just doing it for formalism, plus three moles of hydrogen. And what is its enthalpy of formation? Zero again and again. So, when we do that, we get two times negative 45. Negative 91.8 kilojoules for the system, okay? So, does everybody got that? So, I'm going to erase all this stuff up here so I can rewrite all of you guys a second to do all of you. So, now, each of the system, right? And I guess I didn't write it down, but it says it happens at 298 kelp, okay? So, that's the temperature. So, we should be able to determine the entropy of the surrounding. Is everybody okay with that? Okay. Let's just kind of put this calculation up here. So, that's going to equal negative times negative 91.8 kilojoules divided by 298 kelp, right there. Oftentimes, you'll put these entropy values since they're so small in joules. If you recall from the last problem. So, let's just convert that while we're here. So, I'm going to multiply this by one kilojoule, cancel out our kilojoules there. I get that the change in entropy of the surroundings is 308 joules per kelp. So, everybody got that? Okay. So, it wants to know is does this reaction occur spontaneously at this temperature? Well, we can't tell from this yet. We actually have to plug it into this equation here that we've already come up with, okay? So, I'm going to erase this part. We don't need this number anymore. S of the universe. S of the delta S of the system, 197 joules per kelp. Plus the delta S of the surroundings, which we just calculated, 308 joules per kelp. And again, if you didn't have those in the same units, you couldn't just have them together. So, we're going to calculate this out. So, negative 197 plus 308, I get positive 111, okay? So, 366 to the decimal joules per kelp. Okay? So, that's the answer of the universe. So, what did we say? If that's greater than zero, which it is, is this reaction spontaneous? Yes. So, this is a spontaneous reaction because the delta S is greater than zero. So, the universe gained an angel. Okay? So, that's spontaneous. Any questions about that one? Yeah. The equation has a negative sign in front of it, okay? That's all right. That's a good question. Okay, any other questions? Okay, I wonder.