---
title: "The depletion of stratospheric ozone is proposed to occur according to the two-step mechanism shown below.  \\[ \\text{Step 1: } \\text{Cl(g)} + \\text{O}_3\\text{(g)} \\rightleftharpoons \\text{ClO(g)} + \\text{O}_2\\text{(g)} \\quad (\\text{fast equilibrium}) \\] \\[ \\text{Step 2: } \\text{ClO(g)} + \\text{O}_3\\text{(g)} \\rightarrow \\text{Cl(g)} + 2\\,\\text{O}_2\\text{(g)} \\quad (\\text{slow}) \\]  Which of the following statements correctly identifies the rate law consistent with this mechanism and provides a valid justification for the role of \\(\\text{Cl(g)}\\)?"
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date_modified: "2026-08-23T05:02:07+00:00"
---

# The depletion of stratospheric ozone is proposed to occur according to the two-step mechanism shown below.

\[ \text{Step 1: } \text{Cl(g)} + \text{O}_3\text{(g)} \rightleftharpoons \text{ClO(g)} + \text{O}_2\text{(g)} \quad (\text{fast equilibrium}) \]
\[ \text{Step 2: } \text{ClO(g)} + \text{O}_3\text{(g)} \rightarrow \text{Cl(g)} + 2\,\text{O}_2\text{(g)} \quad (\text{slow}) \]

Which of the following statements correctly identifies the rate law consistent with this mechanism and provides a valid justification for the role of \(\text{Cl(g)}\)?

The depletion of stratospheric ozone is proposed to occur according to the two-step mechanism shown below.

\[ \text{Step 1: } \text{Cl(g)} + \text{O}_3\text{(g)} \rightleftharpoons \text{ClO(g)} + \text{O}_2\text{(g)} \quad (\text{fast equilibrium}) \]
\[ \text{Step 2: } \text{ClO(g)} + \text{O}_3\text{(g)} \rightarrow \text{Cl(g)} + 2\,\text{O}_2\text{(g)} \quad (\text{slow}) \]

Which of the following statements correctly identifies the rate law consistent with this mechanism and provides a valid justification for the role of \(\text{Cl(g)}\)?

- **A.** \(\text{Rate} = k\,\dfrac{[\text{Cl}][\text{O}_3]^2}{[\text{O}_2]}\), because \(\text{Cl(g)}\) is a catalyst that is consumed in Step 1 and regenerated in Step 2, and expressing the intermediate \([\text{ClO}]\) from the pre-equilibrium of Step 1 introduces \([\text{O}_2]\) into the denominator.
- **B.** \(\text{Rate} = k\,[\text{Cl}][\text{O}_3]^2\), because \(\text{Cl(g)}\) is a catalyst that speeds up the reaction, and the rate law depends solely on the reactants consumed up through the slow step without regard to products of reversible steps.
- **C.** \(\text{Rate} = k\,[\text{O}_3]^2\), because \(\text{Cl(g)}\) is an intermediate that cancels out of the overall balanced equation and therefore cannot appear in the experimental rate law.
- **D.** \(\text{Rate} = k\,\dfrac{[\text{ClO}][\text{O}_3]^2}{[\text{Cl}][\text{O}_2]}\), because \(\text{Cl(g)}\) is an inhibitor that reduces the concentration of the intermediate \(\text{ClO(g)}\), thereby decreasing the overall rate.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121406/*