Ch.14 - Chemical Kinetics

Problem 33c

Chapter 14, Problem 33c

The iodide ion reacts with hypochlorite ion (the active ingredient in chlorine bleaches) in the following way: OCl^- + I^- → OI^- + Cl^- . This rapid reaction gives the following rate data:
[OCl₄^-] (M) [I^-] (M) Initial Rate (M,s)
1.5 * 10-3 1.5 * 10-3
1.36 * 10-4 3.0 * 10-3 1.5 * 10-3 2.72 * 10-4
1.5 * 10-3 3.0 * 10-3 2.72 * 10-4 (c) Calculate the rate when [OCl^-] = 2.0 * 10-3 M and [I^-] = 5.0 * 10 - 4 M.

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Identify the rate law for the reaction. The general form is: Rate = k[OCl^-]^m[I^-]^n, where k is the rate constant, and m and n are the reaction orders with respect to OCl^- and I^- respectively.

Use the given data to determine the reaction orders m and n. Compare the initial rates and concentrations from the experiments to find the values of m and n.

Once m and n are determined, use the data from one of the experiments to solve for the rate constant k.

Substitute the values of k, m, n, and the given concentrations [OCl^-] = 2.0 * 10^-3 M and [I^-] = 5.0 * 10^-4 M into the rate law equation.

Calculate the rate using the rate law equation with the substituted values.

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Key Concepts

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

Rate of Reaction

The rate of a chemical reaction measures how quickly reactants are converted into products. It is typically expressed in terms of concentration change over time, such as molarity per second (M/s). Understanding the rate is crucial for predicting how changes in concentration of reactants affect the speed of the reaction, which is essential for solving the given problem.

Rate Law

The rate law is an equation that relates the rate of a reaction to the concentration of its reactants, typically in the form Rate = k[A]^m[B]^n, where k is the rate constant, and m and n are the reaction orders with respect to each reactant. Determining the rate law from experimental data allows us to predict how varying concentrations will influence the reaction rate, which is necessary for calculating the rate under new conditions.

Stoichiometry

Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced chemical equations. It provides the quantitative relationships between substances, allowing for the determination of how much of each reactant is needed or how much product will be formed. In this context, stoichiometry helps in understanding how the concentrations of OCl⁻ and I⁻ will affect the overall reaction rate.

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Related Practice

Textbook Question

The reaction between ethyl bromide (C₂H₅Br) and hydroxide ion in ethyl alcohol at 330 K, C₂H₅Br(alc) + OH^-(alc) → C₂H₅OH(l) + Br^-(alc), is first order each in ethyl bromide and hydroxide ion. When [C₂H₅Br] is 0.0477 M and [OH^-] is 0.100 M, the rate of disappearance of ethyl bromide is 1.7×10^-7 M/s. (c) How would the rate of disappearance of ethyl bromide change if the solution were diluted by adding an equal volume of pure ethyl alcohol to the solution?

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Textbook Question

The iodide ion reacts with hypochlorite ion (the active ingredient in chlorine bleaches) in the following way: OCl^- + I^- → OI^- + Cl^- . This rapid reaction gives the following rate data:

[OCl₄^-] (M) [I^-] (M) Initial Rate (M,s)

1.5 * 10-3 1.5 * 10-3

1.36 * 10-4 3.0 * 10-3 1.5 * 10-3 2.72 * 10-4

1.5 * 10-3 3.0 * 10-3 2.72 * 10-4

(a) Write the rate law for this reaction.

Textbook Question

The iodide ion reacts with hypochlorite ion (the active ingredient in chlorine bleaches) in the following way: OCl - + I - ¡OI - + Cl - . This rapid reaction gives the following rate data:

[OCl₄^-] (M) [I^-] (M) Initial Rate (M,s)

1.5 * 10-3 1.5 * 10-3

1.36 * 10-4 3.0 * 10-3 1.5 * 10-3 2.72 * 10-4

1.5 * 10-3 3.0 * 10-3 2.72 * 10-4

(b) Calculate the rate constant with proper units.

Textbook Question

The following data were measured for the reaction BF₃(g) + NH₃(g) → F₃BNH₃(g):

Experiment [BF₃] (M) [NH₃] (M) Initial Rate (M/s)

1 0.250 0.250 0.2130

2 0.250 0.125 0.1065

3 0.200 0.100 0.0682

4 0.350 0.100 0.1193

5 0.175 0.100 0.0596

(b) What is the overall order of the reaction?

Textbook Question

The following data were measured for the reaction BF₃(g) + NH₃(g) → F₃BNH₃(g):

Experiment [BF₃] (M) [NH₃] (M) Initial Rate (M/s)

1 0.250 0.250 0.2130

2 0.250 0.125 0.1065

3 0.200 0.100 0.0682

4 0.350 0.100 0.1193

5 0.175 0.100 0.0596