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For the reaction Cl_2(aq) + H_2S(aq) → S(s) + 2H^+(aq) + 2Cl^-(aq), the experimentally observed rate law is rate = k[Cl_2][H_2S]. Which mechanism below is consistent with this rate law?

1. A. Cl_2 + H_2S → H^+ + Cl^- + Cl^- + HS^- (slow) Cl^- + HS^- → H^+ + Cl^- + S (fast)
2. B. Cl_2 + H_2S → H^+ + Cl^- + Cl^- + HS^- (fast) Cl^- + HS^- → H^+ + Cl^- + S (slow)
3. C. Cl_2 + H_2S → H^+ + Cl^- + Cl^- + HS^- (slow) Cl^- + HS^- → H^+ + Cl^- + S (slow)
4. D. Cl_2 + H_2S → H^+ + Cl^- + Cl^- + HS^- (fast) Cl^- + HS^- → H^+ + Cl^- + S (fast)

Correct answer: B. Cl_2 + H_2S → H^+ + Cl^- + Cl^- + HS^- (fast) Cl^- + HS^- → H^+ + Cl^- + S (slow)

Solution

The correct option is consistent with the rate law because it identifies the slow step as the rate-determining step, which involves the reactants Cl_2 and H_2S. This aligns with the observed rate law, indicating that the rate depends on the concentrations of both reactants.

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