The rate of decomposition of hydrogen peroxide can be increased by having the re

Question

The rate of decomposition of hydrogen peroxide can be increased by having the reaction occur in the presence of the iodine ion, I-. The reaction is thought to proceed by the following two-step mechanism…
Step 1: H2O2 (aq) + I- (aq) –> H2O (l) + IO- (aq)
Step 2: IO- (aq) + H2O2 (aq) –> H2O (l) + O2 (g) + I- (aq)

I threw out guesses for most of these, but I'd like to know why I'm right or wrong, and see work/explanations shown. This kinetics thing is only making sense to me very slowly. Thank you. :)

a. Write the rate law for each of the elementary processes (steps) of the mechanism. If an intermediate appears in the rate law you must substitute for it.

b. Write the chemical equation for the overall reaction.
My answer: H2O2 (aq) + I (aq) –> H2O (l) + O2 (g) + I (aq)

c. Identify the chemical that acts as a catalyst. Is the catalyst homogeneous or heterogeneous? Identify the substance that is the intermediate.
My answer: IO is the catalyst and it is homogeneous because both substances are aqueous when they mix. IO is also the intermediate.

d. What is it about the mechanistic steps that allows you to distinguish between a catalyst and intermediate?
I’m not sure. This question leads me to believe that IO is either the catalyst or intermediate, but not both. The IO cancels out, but the H2O doesn’t, so I’m pretty sure it’s the intermediate. However, I do not believe that the H2O is the catalyst because it would still be formed from H2O2even in the absence of I-. In the case of I-, I don’t think it’s the catalyst because it’s not a mixture.

e. If the reaction is first order in both the hydrogen peroxide and iodine ion, which step of the mechanism should be labeled as the rate determining step?
My answer: Step 2 because in step 1, all that’s happening is the transfer of one O atom, which is very brief.

Explanation / Answer

a) For the step-I,

rate of reaction, r1 = k1 [ H2O2 ][I- ] = - k1 [ H2O ][IO- ]

for the Step-II,

rate of reaction, r2 = k2 [ H2O2 ][IO-] = - k2 [ H2O ][I- ]

b) The chemcial reaction for overall reaction is as follows

2H2O2 (aq) –> 2H2O (l) + O2 (g)

c) In the reaction, I- (aq) acts as catalyst.

d) In the given reaction I- (aq) is a catalyst while IO- (aq) is intermediate. The intermediate is generated in one step of the reaction and is consumed in second stage of the reaction e.e. IO- (aq). while catalyst is consumed in the reaction but is released in the final step of the reaction.

e) If reaction is first order reaction, the step-I will be the rate determining step. This is because the formation of intermediate is slow reaction and thus, the slow step reaction is considered as rate determining step.

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