Question:
Consider the reaction:
Cl₂(aq) + H₂S(aq) → S(s) + 2H⁺(aq) + 2Cl⁻(aq)
The rate equation for this reaction is:
rate = k[Cl₂][H₂S]
Which of these mechanisms is/are consistent with the rate equation?
A.
Cl₂ + H₂S → H⁺ + Cl⁻ + Cl⁺ + HS⁻ (slow)
Cl⁺ + HS⁻ → H⁺ + Cl⁻ + S (fast)
B.
H₂S rightleftharpoons H⁺ + HS⁻ (fast equilibrium)
Cl₂ + HS⁻ → 2Cl⁻ + H⁺ + S (slow)
Consider the reaction:
Cl₂(aq) + H₂S(aq) → S(s) + 2H⁺(aq) + 2Cl⁻(aq)
The rate equation for this reaction is:
rate = k[Cl₂][H₂S]
Which of these mechanisms is/are consistent with the rate equation?
A.
Cl₂ + H₂S → H⁺ + Cl⁻ + Cl⁺ + HS⁻ (slow)
Cl⁺ + HS⁻ → H⁺ + Cl⁻ + S (fast)
B.
H₂S rightleftharpoons H⁺ + HS⁻ (fast equilibrium)
Cl₂ + HS⁻ → 2Cl⁻ + H⁺ + S (slow)
Show Hint
The rate law must be derivable directly from the slow step of the mechanism
without involving intermediates.
Updated On: Mar 19, 2026
- B only
- Both A and B
- Neither A nor B
- A only
Show Solution
Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Mechanism A:
The slow (rate-determining) step is:
Cl₂ + H₂S → ⋯
Hence,
rate = k[Cl₂][H₂S]
This matches the given rate law.
Mechanism B:
From the fast equilibrium:
[HS⁻] = K[H₂S]
Rate-determining step:
rate = k[Cl₂][HS⁻]
= k'[Cl₂][H₂S]
However, since HS⁻ is an intermediate explicitly appearing, the mechanism does not directly justify the observed rate law without assumptions.
Thus, only mechanism A is consistent.
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