Original Rate Law Equation: R=k[H2O2][I-] Two mechanisms are proposed: Explain w

Question

Original Rate Law Equation: R=k[H2O2][I-]

Two mechanisms are proposed: Explain which mechanism and which step as the rate determining step would best fit the data?

Mechanism 1:

H2O2+I-->H2O+OI-

OI-+H^+->HOI-

HOI+I^- +H^+ -> I2+ H2O

I2+ I^- -> I- 3

Mechanism 2:

H2O2+ I^- +H^+ -> H2O + HOI

HOI + I^- + H^+ -> I2 +H2O

I2 + I^- -> I3^-

So I know that Mechanism I is the correct answer, however, I'm struggling with finding out what the rate determining step is, and how to compare it and prove that Mechanism 1 is correct. Please help

Explanation / Answer

To ensure the correct mechansim we must follow two guidelines:

1. Sum of the elementary steps involved in a reaction must give the balanced equation for the reaction.

2. The experimentally determined rate law should match with the mechanism.

Mechanism 1

H2O2 + I- ----> H2O +OI- (SLOW STEP)

OI- + H+ ----> HOI (FAST STEP)

HOI- + I- + H+ ----> I2 + H2O (FAST STEP)

I2 + I- ----> I3- (FAST STEP)

Here, step 1 is the rate determining step. Since the rate of formation of OI- is slow, it is considered as the intermediate.

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