Ch.15 - Chemical Kinetics

Tro - Chemistry: A Molecular Approach 6th Edition

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Tro 6th Edition

Ch.15 - Chemical Kinetics

Problem 83a

Chapter 15, Problem 83a

Consider this three-step mechanism for a reaction:
Cl₂ (g) k₁⇌k₂ 2 Cl (g) Fast
Cl (g) + CHCl₃ (g) →k₃ HCl (g) + CCl₃ (g) Slow
Cl (g) + CCl₃ (g) →k₄ CCl₄ (g) Fast
a. What is the overall reaction?

Verified step by step guidance

Identify the reactants and products in each step of the mechanism. For the first step, the reactants are Cl2 and the products are 2 Cl. In the second step, the reactants are Cl and CHCl3, and the products are HCl and CCl3. In the third step, the reactants are Cl and CCl3, and the product is CCl4.

Determine the intermediates by identifying species that appear as products in one step and reactants in another. Here, Cl and CCl3 are intermediates as they are produced in one step and consumed in another.

Cancel out the intermediates from the overall reaction. Since Cl and CCl3 are intermediates, they should not appear in the final balanced equation.

Write the overall reaction by combining the remaining reactants and products, ensuring to balance the equation. Start with the initial reactants that are not intermediates and include the final products that are not intermediates.

Check the stoichiometry of the final equation to ensure that the number of atoms of each element is the same on both sides of the equation.

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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 individual elementary steps that lead to the overall reaction, including the formation and consumption of intermediates. Understanding the mechanism helps in predicting the rate and outcome of the reaction.

Elementary Steps

Elementary steps are the individual reactions that make up a reaction mechanism. Each step represents a single molecular event, such as the collision of reactants or the formation of products. The rate of the overall reaction is often determined by the slowest elementary step, known as the rate-determining step.

Overall Reaction

The overall reaction is the net equation that summarizes the reactants and products of a chemical process, derived from the individual elementary steps. It reflects the stoichiometry of the reaction and provides insight into the conservation of mass. To find the overall reaction, one must combine the elementary steps while canceling out any intermediates.

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Textbook Question

Which of these two reactions would you expect to have the smaller orientation factor? Explain. a. O(g) + N2(g) → NO( g) + N(g) b. NO(g) + Cl2(g) → NOCl( g) + Cl(g)

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Textbook Question

Consider these two gas-phase reactions: a. AA(g) + BB(g) → 2 AB(g) b. AB(g) + CD(g) → AC(g) + BD(g) If the reactions have identical activation barriers and are carried out under the same conditions, which one would you expect to have the faster rate?

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Textbook Question

Many heterogeneous catalysts are deposited on high-surfacearea supports. Why?

Consider this three-step mechanism for a reaction:

Cl₂ (g) k₁⇌k₂ 2 Cl (g) Fast

Cl (g) + CHCl₃ (g) →k₃ HCl (g) + CCl₃ (g) Slow

Cl (g) + CCl₃ (g) →k₄ CCl₄ (g) Fast