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Multiple Choice
Consider the proposed mechanism for the decomposition reaction 2 H₂O₂(aq) → 2 H₂O(l) + O₂(g) in the presence of I⁻(aq). What is the rate law for this reaction?
A
Rate = k[H₂O₂]
B
Rate = k[H₂O₂][I⁻]
C
Rate = k[I⁻]²
D
Rate = k[H₂O₂]²
Verified step by step guidance
1
Identify the overall reaction: 2 H₂O₂(aq) → 2 H₂O(l) + O₂(g). This is the decomposition of hydrogen peroxide in the presence of iodide ions (I⁻).
Understand that the rate law is determined by the slowest step in the reaction mechanism, known as the rate-determining step.
Consider the role of the catalyst, I⁻(aq), in the reaction mechanism. Catalysts often appear in the rate law even though they are not part of the overall balanced equation.
Analyze the proposed rate laws: Rate = k[H₂O₂], Rate = k[H₂O₂][I⁻], Rate = k[I⁻]², and Rate = k[H₂O₂]². The correct rate law should include the reactants involved in the rate-determining step.
Conclude that the correct rate law is Rate = k[H₂O₂][I⁻], as it accounts for both the concentration of hydrogen peroxide and the presence of the iodide catalyst, which is consistent with the mechanism involving I⁻ as a catalyst.