Ch.14 - Chemical Kinetics

Brown - Chemistry: The Central Science 14th Edition

Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Not the one you use?Change textbook

Brown 14th Edition

Ch.14 - Chemical Kinetics

Problem 8

Chapter 14, Problem 8

The addition of NO accelerates the decomposition of N2O, possibly by the following mechanism: NO(g) + N2O(g) ⟶ N2(g) + NO2(g) 2 NO2(g) ⟶ 2 NO(g) + O2(g). (c) If experiments show that during the decomposition of N2O, NO2 does not accumulate in measurable quantities, does this rule out the proposed mechanism?

Name: Chemistry: The Central Science
Author: Brown
ISBN: 9780134414232

Verified step by step guidance

Understand the proposed mechanism: The mechanism consists of two steps. The first step is the reaction between NO and N2O to form N2 and NO2. The second step involves the decomposition of NO2 to regenerate NO and produce O2.

Consider the implication of NO2 not accumulating: If NO2 does not accumulate, it suggests that NO2 is being consumed as quickly as it is being produced. This means the second step of the mechanism is likely very fast compared to the first step.

Analyze the rate of each step: For NO2 not to accumulate, the rate of the second step (2 NO2 ⟶ 2 NO + O2) must be equal to or greater than the rate of the first step (NO + N2O ⟶ N2 + NO2). This ensures that NO2 is used up as soon as it is formed.

Evaluate the mechanism: The lack of NO2 accumulation does not necessarily rule out the proposed mechanism. It suggests that the second step is fast, which is consistent with the mechanism if NO2 is a transient intermediate.

Conclude based on experimental observations: Since NO2 does not accumulate, the proposed mechanism is plausible. The fast consumption of NO2 aligns with the mechanism, indicating that the steps are occurring as described without contradicting the experimental observations.

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 the pathway by which reactants are converted into products. It outlines the individual elementary steps involved in a chemical reaction, including the formation and consumption of intermediates. Understanding the mechanism helps in predicting the behavior of reactants and products under various conditions.

Intermediates

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 transiently. In the context of the proposed mechanism, if NO2 is formed but does not accumulate, it suggests that it is being rapidly converted to other species, indicating its role as an intermediate.

Steady-State Approximation

The steady-state approximation is a method used in reaction kinetics to simplify the analysis of complex reactions. It assumes that the concentration of intermediates remains relatively constant over the course of the reaction, meaning their formation and consumption rates are equal. If NO2 does not accumulate, it supports the idea that the steady-state condition is met, allowing for the proposed mechanism to still be valid.

Related Practice

Textbook Question

The accompanying graph shows plots of ln k versus 1>T for two different reactions. The plots have been extrapolated to the y-intercepts. Which reaction (red or blue) has (b) the larger value for the frequency factor, A? [Section 14.5]

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Textbook Question

The following graph shows two different reaction pathways for the same overall reaction at the same temperature. Is each of the following statements true or false? (b) For both paths, the rate of the reverse reaction is slower than the rate of the forward reaction.

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Textbook Question

The following diagrams represent mixtures of NO(g) and O21g2. These two substances react as follows: 2 NO1g2 + O21g2¡2 NO21g2 It has been determined experimentally that the rate is second order in NO and first order in O2. Based on this fact, which of the following mixtures will have the fastest initial rate? [Section 14.3]

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Textbook Question

You study the rate of a reaction, measuring both the concentration of the reactant and the concentration of the product as a function of time, and obtain the following results:

Which chemical equation is consistent with these data: (i) A → B, (ii) B → A, (iii) A → 2 B, (iv) B → 2 A?

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Textbook Question

Consider the diagram that follows, which represents two steps in an overall reaction. The red spheres are oxygen, the blue ones nitrogen, and the green ones fluorine. (d) Write the rate law for the overall reaction if the first step is the slow, rate-determining step. [Section 14.6]

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Textbook Question

Given the following diagrams at t = 0 min and t = 30 min

After four half-life periods for a first-order reaction, what fraction of reactant remains? [Section 14.4]