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Ch.14 - Chemical Kinetics
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook
All textbooksBrown 14th EditionCh.14 - Chemical KineticsProblem 72b
Chapter 14, Problem 72b

The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism:
H2O2(aq) + I-(aq) → H2O(l) + IO-(aq) (slow)
IO-(aq) + H2O2(aq) → H2O(l) + O2(g) + I-(aq) (fast)
(b) Identify the intermediate, if any, in the mechanism.

Verified step by step guidance
1
Step 1: Understand the concept of reaction intermediates. A reaction intermediate is a species that is produced in one step of a reaction mechanism and consumed in a subsequent step. It does not appear in the overall chemical equation for the reaction.
Step 2: Look at the given reaction mechanism. The first step produces H2O and IO-. The second step consumes IO- and produces H2O, O2, and I-.
Step 3: Identify the species that is produced in the first step and consumed in the second step. In this case, it is IO-.
Step 4: Confirm that this species does not appear in the overall chemical equation for the reaction. The overall equation is obtained by adding the two steps together and cancelling out any species that appear on both sides. In this case, IO- does not appear in the overall equation.
Step 5: Conclude that IO- is the reaction intermediate in this mechanism.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Reaction Mechanism

A reaction mechanism is a step-by-step description of how a chemical reaction occurs at the molecular level. It outlines the sequence of elementary steps that lead to the formation of products from reactants. Understanding the mechanism helps in identifying intermediates, which are species formed during the reaction but not present in the final products.
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Reaction Mechanism Overview

Intermediates

Intermediates are transient species that appear in the course of a reaction mechanism but do not appear in the overall balanced equation. They are formed in one step and consumed in a subsequent step. Identifying intermediates is crucial for understanding the pathway of the reaction and the role of catalysts.
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Catalysis

Catalysis is the process by which the rate of a chemical reaction is increased by the presence of a catalyst, which is not consumed in the reaction. Catalysts work by providing an alternative pathway with a lower activation energy. In the given reaction, iodide ion acts as a catalyst, facilitating the decomposition of hydrogen peroxide through the formation of intermediates.
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Related Practice
Textbook Question

The reaction 2 NO1g2 + Cl21g2¡2 NOCl1g2 was performed and the following data were obtained under conditions of constant 3Cl24:

(a) Is the following mechanism consistent with the data? NO1g2 + Cl21g2ΔNOCl21g2 1fast2 NOCl21g2 + NO1g2¡2 NOCl1g2 1slow2

Textbook Question

The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism:

H2O2(aq) + I-(aq) → H2O(l) + IO-(aq) (slow)

IO-(aq) + H2O2(aq) → H2O(l) + O2(g) + I-(aq) (fast)

(a) Write the chemical equation for the overall process.

Textbook Question

The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism:

H2O2(aq) + I-(aq) → H2O(l) + IO-(aq) (slow)

IO-(aq) + H2O2(aq) → H2O(l) + O2(g) + I-(aq) (fast)

(c) Assuming that the first step of the mechanism is rate determining, predict the rate law for the overall process.

Textbook Question

Consider the following energy profile.

(c) Which step is rate limiting?