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Ch.14 - Chemical Kinetics
Chapter 14, Problem 54b

This reaction was monitored as a function of time: AB → A + B A plot of 1/[AB] versus time yields a straight line with a slope of +0.55/Ms. b. Write the rate law for the reaction.

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Identify the order of the reaction by analyzing the plot. A straight line in a plot of 1/[AB] versus time indicates a second-order reaction.
For a second-order reaction, the rate law is expressed as: rate = k[AB]^2.
The slope of the line in the plot of 1/[AB] versus time is equal to the rate constant k for a second-order reaction.
Given that the slope is +0.55/Ms, this value represents the rate constant k.
Therefore, the rate law for the reaction is: rate = 0.55 [AB]^2.

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Key Concepts

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

Rate Law

The rate law of a chemical reaction expresses the relationship between the rate of the reaction and the concentration of its reactants. It is typically formulated as rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the orders of the reaction with respect to reactants A and B. Understanding the rate law is essential for predicting how changes in concentration affect the reaction rate.
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Order of Reaction

The order of a reaction refers to the power to which the concentration of a reactant is raised in the rate law. It indicates how the rate of reaction is affected by the concentration of that reactant. In this case, since the plot of 1/[AB] versus time is linear, it suggests that the reaction is second-order with respect to AB, meaning the rate is proportional to the square of the concentration of AB.
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Integrated Rate Laws

Integrated rate laws relate the concentration of reactants to time and are derived from the differential rate laws. For a second-order reaction, the integrated rate law is given by 1/[AB] = kt + 1/[AB]0, where [AB]0 is the initial concentration. The linear relationship observed in the plot indicates that the reaction follows this integrated form, allowing us to determine the rate constant from the slope.
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