8. A proposed mechanism for the decomposition of hydrogen peroxide (H2O2) consists of three elementary steps:

H2O2(g) → 2OH(g)
H2O2(g) + OH(g) → H2O(g) + HO2(g)
HO2(g) + OH(g) → H2O(g) + O2(g)

The rate law of the reaction is first order with respect to H2O2(g). Which step of the mechanism is the rate-determining step?

A. The first step.
B. The third step.
C. Reactions in the gas phase do not have rate determining steps.
D. Steps 1 and 2 are both rate detemining steps.
E. The second step.

Looking at the mechanism, if the reaction is first order with respect to hydrogen peroxide then it implies that the first step involving the formation of hydroxide radicals must be the slowest step and the rate determining step. This step depends only on the hydrogen peroxide concentration. since the reaction is first order with respect to hydrogen peroxide, the first step must be the rate determining step of the reaction.

throwdolbeau throwdolbeau · Answer 2 · 2022-03-01T13:13:37+01:00

The mechanism that is the rate-determining step is:

A. The first step

Proposed mechanism:

Step 1: H₂O₂(g) → 2OH(g) (slow)

Step 2: H₂O₂(g) + OH(g) → H₂O(g) + HO₂(g) (fast)

Step 3: HO₂(g) + OH(g) → H₂O(g) + O₂(g) (fast)

If the reaction is first order with respect to hydrogen peroxide then it implies that the first step involving the formation of hydroxide radicals must be the slowest step and the rate determining step. This step depends only on the hydrogen peroxide concentration. since the reaction is first order with respect to hydrogen peroxide, the first step must be the rate determining step of the reaction.

Thus, correct option is A.

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