Ch.14 - Chemical Kinetics

Problem 74

Chapter 14, Problem 74

(c) What are the intermediates in this mechanism? (d) If you are unable to detect HOBr or HOOBr among the products, does this disprove your mechanism?

Verified step by step guidance

Step 1: Understand the concept of reaction intermediates. Intermediates are species that are formed during the reaction process but do not appear in the overall balanced equation. They are typically unstable and short-lived.

Step 2: Analyze the given mechanism to identify intermediates. Look for species that are produced in one step and consumed in another, without appearing in the final products.

Step 3: Consider the role of HOBr and HOOBr in the mechanism. If these species are formed and consumed within the reaction steps, they are likely intermediates.

Step 4: Evaluate the significance of detecting intermediates. The inability to detect HOBr or HOOBr among the products does not necessarily disprove the mechanism, as intermediates are often transient and may not be present in measurable quantities at the end of the reaction.

Step 5: Consider alternative methods to support the mechanism. Even if intermediates are not directly detected, other evidence such as kinetic studies or indirect observations can support the proposed mechanism.

Key Concepts

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

Reaction Intermediates

Reaction intermediates are species that are formed during the course of a chemical reaction but are not present in the final products. They are typically unstable and exist only for a short duration. Understanding intermediates is crucial for elucidating the mechanism of a reaction, as they provide insight into the steps and transitions that occur from reactants to products.

Mechanism of a Reaction

The mechanism of a reaction describes the step-by-step sequence of elementary reactions by which overall chemical change occurs. It includes details about the formation and consumption of intermediates, the transition states, and the energy changes involved. A clear understanding of the mechanism helps predict the products and the conditions under which the reaction occurs.

Detection of Reaction Products

The detection of reaction products is essential for validating a proposed reaction mechanism. If expected products, such as HOBr or HOOBr, are not detected, it raises questions about the accuracy of the mechanism. However, the absence of certain products does not necessarily disprove the mechanism, as intermediates may not be stable enough to be isolated or detected under the reaction conditions.

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Guided course

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Production of Hydrogen Example

Related Practice

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)

(b) Identify the intermediate, if any, in the mechanism.

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)

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

You have studied the gas-phase oxidation of HBr by O₂: 4 HBr(g) + O₂(g) → 2 H₂O(g) + 2 Br₂(g)

You find the reaction to be first order with respect to HBr and first order with respect to O₂. You propose the following mechanism:

HBr(g) + O₂(g) → HOOBr(g)

HOOBr(g) + HBr(g) → 2 HOBr(g)

HOBr(g) + HBr(g) → H₂O(g) + Br₂(g)

(a) Confirm that the elementary reactions add to give the overall reaction.

Textbook Question

You have studied the gas-phase oxidation of HBr by O₂: 4 HBr(g) + O₂(g) → 2 H₂O(g) + 2 Br₂(g)

You find the reaction to be first order with respect to HBr and first order with respect to O₂. You propose the following mechanism:

HBr(g) + O₂(g) → HOOBr(g)

HOOBr(g) + HBr(g) → 2 HOBr(g)

HOBr(g) + HBr(g) → H₂O(g) + Br₂(g)

(b) Based on the experimentally determined rate law, which step is rate determining?

Textbook Question

(a) What is a catalyst? (b) What is the difference between a homogeneous and a heterogeneous catalyst?