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Ch.15 - Chemical Kinetics
Chapter 15, Problem 44a

A reaction in which A, B, and C react to form products is zero order in A, one-half order in B, and second order in C. a. Write a rate law for the reaction.

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Identify the general form of the rate law: \( \text{Rate} = k[A]^m[B]^n[C]^p \).
Determine the order of reaction with respect to each reactant: \( m = 0 \) for A, \( n = \frac{1}{2} \) for B, and \( p = 2 \) for C.
Substitute the orders into the rate law expression: \( \text{Rate} = k[A]^0[B]^{1/2}[C]^2 \).
Simplify the expression by noting that any concentration raised to the power of zero is 1: \( \text{Rate} = k[B]^{1/2}[C]^2 \).
The final rate law for the reaction is \( \text{Rate} = k[B]^{1/2}[C]^2 \).

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Key Concepts

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

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. For example, a zero-order reaction means the rate is independent of the concentration of that reactant, while a first-order reaction means the rate is directly proportional to its concentration.
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Rate Law

The rate law is an equation that relates the rate of a chemical reaction to the concentrations of the reactants, each raised to a power corresponding to its order in the reaction. It is typically expressed in the form: Rate = k[A]^m[B]^n[C]^p, where k is the rate constant, and m, n, and p are the orders of the reactants A, B, and C, respectively. Understanding the rate law is crucial for predicting how changes in concentration affect the reaction rate.
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Rate Constant (k)

The rate constant, denoted as k, is a proportionality factor in the rate law that is specific to a given reaction at a specific temperature. It reflects the intrinsic speed of the reaction and is influenced by factors such as temperature and the presence of catalysts. The value of k can vary with the order of the reaction and is essential for calculating the rate of the reaction under different conditions.
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Related Practice
Textbook Question

This reaction is first order in N2O5: N2O5(g) → NO3(g) + NO2(g) The rate constant for the reaction at a certain temperature is 0.053/s. b. What would the rate of the reaction be at the concentration indicated in part a if the reaction were second order? Zero order? (Assume the same numerical value for the rate constant with the appropriate units.)

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Textbook Question

A reaction in which A, B, and C react to form products is first order in A, second order in B, and zero order in C. b. What is the overall order of the reaction?

Textbook Question

A reaction in which A, B, and C react to form products is first order in A, second order in B, and zero order in C c. By what factor does the reaction rate change if [A] is doubled (and the other reactant concentrations are held constant)? d. By what factor does the reaction rate change if [B] is doubled (and the other reactant concentrations are held constant)? e. By what factor does the reaction rate change if [C] is doubled? f. By what factor does the reaction rate change if the concentrations of all three reactants are doubled?

Textbook Question

A reaction in which A, B, and C react to form products is zero order in A, one-half order in B, and second order in C. c. By what factor does the reaction rate change if [A] is doubled (and the other reactant concentrations are held constant)? d. By what factor does the reaction rate change if [B] is doubled? e. By what factor does the reaction rate change if [C] is doubled? f. By what factor does the reaction rate change if [C] is doubled (and the other reactant concentrations are held constant)?

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Textbook Question

Consider the tabulated data showing the initial rate of a reaction (A → products) at several different concentrations of A. What is the order of the reaction? Write a rate law for the reaction including the value of the rate constant, k.

[A] (M) Initial Rate (M/s)

0.050 0.100

0.075 0.225

0.090 0.324