 Okay, so let's try this one. It says 2.50 mole quantity of nitrosyl chloride was initially in a 1.50 liter reaction chamber at 400 degrees Celsius. After equilibrium was established, it was found that 28.0% of the nitrosyl chloride had dissociated. And it gives you the reaction equation up there. And it wants you to calculate the equilibrium constant for this reaction. Okay, so that's all it gives us. And we need to calculate the equilibrium constant. So I guess the first thing we want to write down is what is the equation for the equilibrium constant? So the equilibrium constant Kc is going to be the concentration of the products, right guys? The concentration of the products raised to their coefficients divided by the concentration of the reactants raised to their coefficients. Okay, so everybody should have been able to do that right now. Okay, so that implies, right, that we need to get the concentrations of all of these things. And remember that's an equilibrium, right? So here we have the number of moles we put in to begin with and the volume we started with. So that's original. So let's calculate that first. So the concentration of nitrosyl chloride originally, right, is going to be 2.50 moles divided by 1.50 liters. So when we do that, 1.67 molar NOCl. Okay? So that's at the beginning, that's initially, right? So that's not what happens though at equilibrium, or that's not the concentration in equilibrium. In order to figure that out, we have to do an ice table, okay? So it also gives us a clue as to what's happening in equilibrium, okay? So this is being 28% dissociated. So let's just keep that in mind. So let's write our ice tables. ICB, okay? So they're all gases, so they're all going to be image. And we know that, again, both from the reaction equation and the equilibrium constant expression, we know this is 1.67 molar. And we didn't have any of this, and we didn't have any of this to start out, okay? So from this, we're going to subtract, we're going to add, and we're going to add, right? So we're going to do the number of coefficients, okay? So we're going to do minus 2x plus 2x plus x. Will we go with that? Okay, wonderful. So let's just go ahead and solve these three expressions, right? 1.67 minus 2x is 1.67 minus 2x, okay? So 0 plus 2x is 2x, 0 plus x is x, like that, okay? So hopefully you can see well we're probably going to need to solve for x, okay? Especially since we don't have kc, okay? So that was the difference. Most of the time we have this kc and we can do our quadratic formula or whatever and solve for x. But we can't do that this time. But we have this percent dissociation. So that really helps us out, okay? So remember that means the percent reacted, because this is a dissociation reaction, okay? So the percent dissociated, we can think of it like this. This is going to be the change in molarity divided by the original molarity times 100%, okay? So we have the original molarity, right? We have the percent dissociation and we have 100%. So we can figure out that change in molarity. And that's going to see, notice that's the change in molarity too, okay? So we're going to set that thing equal to that thing there, 2x minus 2x, okay? Is everybody okay with that? Yes. Okay, so let's re-convert this and solve for that change in molarity, okay? So delta m is going to equal percent dissociated times the original concentration molarity original divided by 100%. So it's just a plug and chug expression now. So we've got 28.0% times original molarity, 1.67 molars divided by 100%. Percents cancel like that. So that change is 0.467 molar. So 0.467 molar is going to equal 2x, okay? Because that's how much it changed. And we don't have to worry about that negative sign because it's going to be negative on this side, positive on that side, okay? So we're just worrying how much it changed, okay? You okay with that? Yeah. Okay, wonderful. So let's just accept those two expressions equal to each other. Let's do it up here. So 2x equals 0.467 molar, right? So x is going to equal 0.233 molar, effective. Is it okay with that? Yeah. So we're up here. Yeah. Okay. So what did we say? Well, x equals 0.233. So can I just replace that? 0.233. Okay, 2x, well, we know that that equals 0.467 molar, okay? And then 1.67 minus 2x. Well, let's do that. 1.67 minus 2x. And it's going to be 1.220, okay? We'll see. Is everybody okay with that? There's some more significant figures that it gives on your copy, but I'm just going to go over it. Okay, so now we have the concentration of nitrosyl chloride at equilibrium. Is everybody okay with that? Yes. Okay, so let's just write it out if you guys want to. So this is NOCl at equilibrium, right? Molar, okay? This is the concentration of NO at equilibrium, molar, right? This is the concentration of NOCl2 at equilibrium, molar. So now let's plug those values in. Did you already get it? Did you get the right answer? Okay. Hopefully you did. Okay, so let's see. We want nitrogen monoxide, right? So first is going to be 0.467. I'm going to square that and multiply that by chlorine, which is 0.233. And remember in these KCs, KQs, all that stuff, we don't put any units, okay? I know oftentimes we want to. And then at the bottom, 1.20 squared. 0.467 squared times 1.233 divided by 1.2. And I got something like 0.0353 as my case. Okay? So this is a kind of long process, but if you think about it in the right way, it really does make sense, okay? The one thing that oftentimes gets confusing is that you've got to remember that this is the change as opposed to what you're ended up with, okay? If you wanted to say 72%, that would equal 1.67 minus 2x, okay? So the other one, 28% equals 2x, okay? Any questions on that one before we kill it? Wonderful. Good job, guys.