12.7 Exercise 3

Consider this scenario and answer the following questions: Chlorine atoms resulting from decomposition of chlorofluoromethanes, such as CCl₂F₂, catalyze the decomposition of ozone in the atmosphere. One simplified mechanism for the decomposition is:
$\begin{matrix} \\ \\ \text{O}_{3} \overset{ \text{sunlight} }{\rightarrow} \text{O}_{2} + \text{O} \\ \text{O}_{3} + \text{Cl} \rightarrow \text{O}_{2} + \text{ClO} \\ \text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_{2}\end{matrix}$

(a) Explain why chlorine atoms are catalysts in the gas-phase transformation:
$2 \text{O}_{3} \rightarrow 3 \text{O}_{2}$

(b) Nitric oxide is also involved in the decomposition of ozone by the mechanism:
$\begin{matrix} \\ \text{O}_{3} \overset{ \text{sunlight} }{\rightarrow} \text{O}_{2} + \text{O} \\ \text{O}_{3} + \text{NO} \rightarrow \text{NO}_{2} + \text{O}_{2} \\ \text{NO}_{2} + \text{O} \rightarrow \text{NO} + \text{O}_{2}\end{matrix}$

Is NO a catalyst for the decomposition? Explain your answer.