 OK, so let's do the writing of this reaction quotient and finding the overall k. And we've got some elementary steps here. So this problem says, understanding reactions involving normal components of air is essential for solving problem sealing with atmospheric pollution. Here's a reaction sequence involving nitrogen and oxygen, the most abundant gases in air. Nitrogen dioxide is a toxic pollutant that contributes to photochemicals tomorrow. OK. So the elementary steps, or the two reaction steps that we see up here, have qc's themselves, OK? So let's figure out what those qc's are of these two reactions. So we'll call this reaction 1 and this one reaction 2. So qc1 is going to be the concentration of anano squared. Everybody OK with that? Divided by the concentration of n2 times the concentration of o2. Like that. qc2 is going to be equal to the concentration of anano2 squared divided by the concentration of anano squared times the concentration of o2. OK, is everybody OK with that? So let's go ahead and figure out what this overall reaction is. Do you guys remember how to do that? Don't remember it from yesterday? What do we do? If there's something on this side of the reactants and on the reaction and that side of the reaction, what do we do? It's canceling. I'm glad we remember, OK? So nitrogen, is that on both sides? No. Oxygen, no. What about this 2-n-o gas? Yeah, so let's get rid of that one. And oxygen, no, and 2-n-o-2, right? So this would be the overall reaction. Let's add it up now. So n2 gas plus 2-o-2 gas goes back and forth to 2-n-o-2 gas. Is everybody OK with figuring out what the overall reaction is? This k here, so we'll say kc1, kc2. This is going to be k, we're going to say, of the overall. And what is that going to equal? You guys remember? How are we going to figure it out? How about that? kc1 times what? kc2. That should give us that k, OK? So let's figure out what the q for this reaction sequence is, or this reaction is down here, the overall reaction. So I'm going to say q overall down here. And I'm going to, right on the top, n-o-2 squared, denominator times hydrogen times o-2 squared. Would everybody have written that one? Wonderful. OK, so I want to show you something. If I take qc1 and qc2 that we've gotten here, and I multiply those together, I should get the qc overall, because that would be the same similar thing as doing this, OK? So if I don't get that, then something has gone wrong, OK? So let's do that, squared, like that. What do I get on the top? 2 squared, like that. And on the bottom, n-2 put 2 squared. Does everybody see that? Notice it's the same as this down here, OK? So you can figure it out either way. So that's what this one's saying. Show that the qc, the overall qc for this reaction sequence, is the same as the product of the individual qc's for the individual reactions, OK? So does that prove that to everybody? Is that OK for everybody? Wonderful. You guys are doing awesome. OK, I'm going to have to erase some of this to do the next part. Is that all right? Everybody got this stuff written down? So that's the qc over all. And we don't know if this reaction is at equilibrium or not at equilibrium, because we don't have any values of the concentration units, OK? But we could figure out what the overall k would be by multiplying the two k's together. So k overall is going to be exactly what we showed there. kc1, so 4.3 times 10 to the negative 25 times kc2, which is 6.4 times 10 to the 9. That's going to equal 2 6-pigs, right? So I got 2.8 times 10 to the negative 15. So remember, kq is one of the few things in chemistry that don't have units associated with them, OK? Even though, if you could imagine, this would be molar squared, right? This would be molar, this would be molar squared, right? So even though you're going to have all these different kind of molarity units, you're just going to get rid of them at the end. So there's no use in trying to keep your units. So I know those of you who have had me for two semesters now have been busting your bonk, this is about keeping your units, OK? But this time, you're just going to wipe them clean, OK? So no units on this one. So don't put per molar for this one, if that makes sense, OK? Any questions before this dies? OK, one.