 Okay, let's try this one. It says sulfur dioxide reacts with oxygen in the present presence of platinum to give sulfur trioxide the reaction is shown. Suppose that at one stage of the reaction 24.1 moles of sulfur dioxide 79.0 moles of oxygen and 23 moles of sulfur trioxide are present in the reaction. Vessel at total pressure of 0.9238m. Calculate the mole fraction of sulfur trioxide and its partial pressure. Okay, so the first thing you want to do when you're doing something like this is you want to find the mole fraction of, well it says to find the mole fraction of the sulfur dioxide, but in order to do that you need to know the total number of moles. We know the number of moles of sulfur trioxide right here. Okay, so in order to find the total number of moles all you do is add up all three of the moles present in the reaction. Okay, so we got gas, gas and gas. So they're all three present at the reaction at a particular time. So at that particular time what is the total number of moles? That's what we're going to figure out. Okay, so in order to do that you just simply add them all up. So number of moles total is going to be 24.1 moles, 9.0 moles and 23, I think in the problem it says 24.0 moles. So let's change that. So we don't have any significant figure of issues here. Okay, and then just add those three numbers up. So 24.1 plus 79 plus 23 is, yeah, 123.1 moles. So that's the total number of moles of gas you have in the reaction mixture at this particular time. Okay, so then it asks you, well what's the mole fraction of sulfur trioxide? Okay, so mole fraction big X. Okay, sulfur trioxide. Well we know the number of moles of sulfur trioxide and we know the total number of moles. Okay, so remember the mole fraction is just the number of moles of the part divided by the total number of moles. So we have both of those. So if you look here we just figure that out. 23.0 moles divided by 123.1 moles and so the mole fraction and it should be a number that makes sense to you, right? So like 18 percent or point one eight, that makes sense, right? When you look at 23 compared to 126. So if you got some number that's like 72, right, 72, that doesn't make any sense. So it's going to be a fraction. So 0.1 and there's three significant figures of 182. And moles and moles cancel out the fraction. This mole fraction doesn't matter when you do that. And then it asks for, what was it? The last thing it asks for was the pressure of the sulfur trioxide. Right? At this point in time. So pressure. Right? So this one sounds a lot scarier than what it actually is. So the partial pressures of these gases are correlated with the number of moles. So the mole fraction helps you out in that. Right? So if you know the total pressure and you know the mole fraction you just multiply those things together and you get the partial pressure. Okay? So what did we say? The mole fraction of the sulfur trioxide is 0.182 and we multiply that by the total pressure. So you're in front of the camera right now being recorded. What? Yeah. So the partial pressure of sulfur trioxide is 0.168. Any questions on that? No sir, thank you.