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LJ
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Problem 110 Hard Difficulty

A proposed two-step mechanism for the destruction of ozone in the upper atmosphere is
a. What is the overall balanced equation for the ozone destruction reaction?
b. Which species is a catalyst?
c. Which species is an intermediate?
d. What is the rate law derived from this mechanism if the first step in the mechanism is slow and the second step is fast?
e. One of the concerns about the use of Freons is that they will migrate to the upper atmosphere, where chlorine atoms can be generated by the reaction
$$
\mathrm{CCl}_{2} \mathrm{F}_{2} \stackrel{\mathrm{hv}}{\longrightarrow} \mathrm{CF}_{2} \mathrm{Cl}+\mathrm{Cl}
$$
Chlorine atoms also can act as a catalyst for the destruction of ozone. The first step of a proposed mechanism for chlorine-catalyzed ozone destruction is
$$
\mathrm{Cl}(g)+\mathrm{O}_{3}(g) \longrightarrow \mathrm{ClO}(g)+\mathrm{O}_{2}(g)
$$
Assuming a two-step mechanism, propose the second step in the mechanism and give the overall balanced equation.

Answer

a. \mathrm{O}_{3}+\mathrm{O} \longrightarrow 2 \mathrm{O}_{2}
b. \text { NO }
c. \mathrm{NO}_{2}
d. \text { Rate }=k\left[\mathrm{O}_{3}\right][\mathrm{NO}]

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Video Transcript

So in this video, we're gonna work through question 100 ton from chapter 20 which says a proposed to start mechanism of destruction of ozone in the upper atmosphere is given below. So right here, where the red out of their oxygen and the blue Adams or nitrogen? Um, And then in question, they were asked, what is the overall balanced equation for the ozone destruction reaction? Eso Let's take, uh, this image and translate it into a balanced equation are two steps in a balanced equation. And then we'll add those two steps together to get the overall balanced equation. So this is 03 this is in Oh, um, and this is ino too. So, um, let's go ahead and write this out. So we have both three plus ino yields, you know, two plus 02 I'm willing to take a second to check if this, uh, this first reaction is balanced. We have four oxygen atoms and to nitrogen atoms on both sides. So we're good. Um, and then the second step is ino too close. Oh, yield in oh, plus 02 And again, we have three oxygen atoms on both sides and to nitrogen atoms on both sides with that's balance arms, let's add them together to get the overall reaction. Now Ino appears on both the reactor in product side, and so does N 02 So those two are gonna cancel out and we're left with 03 plus oh, yields to go to. So that's that's the answer to a That's our auroral balanced equation and then and be were asked which species is a catalyst. So a catalyst is something that participates in reaction, Um, but is reproduced at the end of the reaction. So it's not used that by the reaction we have our panelists beginning it, uh, is used to further the reaction and that it's reproduced at the end. So in this case, that would be in oh so in owes reacting with ozone and the the first step in reaction mechanism. But in the second step, it's being produced s o the species that the catalyst is in. Oh, and then we want to know which species of the intermediate so in intermediate is a species that is produced by one step in the mechanism and the later consumed in another step in the mechanism it doesn't appear in the overall equation. Same as a catalyst doesn't appear in the overall equation. So which species is an intermediate? Well, you know, two is produced in the first step in our reaction mechanism, but it is not up. It is then consumed is reacting in the second step of reaction mechanism. So which speech is an intermediate? That's a no to. And then Indy were asked, What is the rate law for this mechanism? If the first up in the mechanism is slow and the second step is fast, so the rate law for reaction depends on the slow step in the mechanism. So you take the slows up in the mechanism and you have your rate constant times, your concentration of reactant raised to their striking metric coefficients or their molecular arat e on. So in this case, are slow step is the first step in the reactions where reacting czar 03 and oh, and they're striking metric coefficients or one. So our rate is equal to our great constant K times. 03 concentration times in oh, concentration. And finally e one of the concerns about the use of free ons is that they will migrate into the upper atmosphere, where chlorine atoms could be generated by the reaction where CCL two F two on plus light gives us CF to see L plus a quarry. Adam Um Cory Adams can also act as a catalyst for the destruction of ozone. The first step of a proposed mechanism for the Korean catalyzed ozone destruction is C L plus oh three guild Cielo plus O two, assuming a two step mechanism proposed the second step in the neck things, um, and give the overall balanced equation. So let's use our, um, use Our other ozone destruction mechanism is guidance. So you can kind of see some parallels between the first step in this mechanism and the first step in our other mechanism. So the first step in our other mechanism was, 03 plus in, oh, yields, you know, two plus 02 And in this one, we have, 03 plus e l yield Cielo plus oh, too. So what's changed? Instead of inner, we have seal and instead of you know two, we have steel. Oh, so since you know, was a catalyst and ino too was an intermediate in the overall reaction. Um, then in this flooring catalyzed mechanism, Corinne was the catalyst. And seal owes the intermediate eso We can, uh, right our second step in the mechanism using the second stuff. And the other mechanism is guidance. So we have our intermediate, which is Cielo. Um and we're gonna reacted in oxygen, Adam in the same way that we did in the first mechanism. And then we're going to produce our catalyst, which was C. L. And our other product is owed to S O. That seems like a valid mechanism that let's add them together to get the overall reaction. So again, our catalyst appears Botha's reacted as a product in our intermediate appears both as a product and a reactant. So those air going to cancel out and our overall reaction is actually the same as it was for the other mechanism. It's 03 was oh, yields to go to