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Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and KineticsProblem 31b
Chapter 6, Problem 31b

The rate of the reaction of methyl chloride with hydroxide ion is linearly dependent on both the concentration of methyl chloride and the concentration hydroxide ion. At 30 °C, the constant (k) for the reaction is 1.0 × 10-5 M-1 s-1
b. If the concentration of methyl chloride is decreased to 0.010 M, what will be the effect on
1. the rate of the reaction?
2. the rate constant for the reaction?

Verified step by step guidance
1
Step 1: Recognize that the reaction follows second-order kinetics because the rate is linearly dependent on both the concentration of methyl chloride ([CH3Cl]) and hydroxide ion ([OH⁻]). The rate law can be expressed as: r=k⋅[CH3Cl]⋅[OH−.
Step 2: Understand that the rate constant (k) is a property of the reaction and depends only on temperature. Since the temperature (30 °C) is constant, the rate constant (k = 1.0 × 10⁻⁵ M⁻¹ s⁻¹) will remain unchanged regardless of the change in concentration of methyl chloride.
Step 3: To determine the effect on the rate of the reaction, note that the rate is directly proportional to the concentration of methyl chloride. If the concentration of methyl chloride is decreased to 0.010 M, substitute this value into the rate law equation to observe the proportional change in the rate.
Step 4: Compare the new rate to the original rate. If the original concentration of methyl chloride was higher, say [CH3Cl]₀, the new rate will be reduced proportionally by the ratio of the new concentration (0.010 M) to the original concentration ([CH3Cl]₀). This demonstrates that the rate decreases as the concentration of methyl chloride decreases.
Step 5: Summarize the effects: (1) The rate of the reaction will decrease proportionally to the decrease in the concentration of methyl chloride. (2) The rate constant (k) will remain unchanged because it is independent of reactant concentrations and depends only on temperature.

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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 refers to the speed at which reactants are converted into products. It is typically expressed in terms of the change in concentration of a reactant or product over time. In this case, the rate is directly proportional to the concentrations of both methyl chloride and hydroxide ion, indicating a second-order reaction.
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Rate Constant (k)

The rate constant (k) is a proportionality factor that relates the rate of a reaction to the concentrations of the reactants. It is specific to a given reaction at a particular temperature. In this scenario, the rate constant remains unchanged regardless of the concentrations of the reactants, as it is a characteristic of the reaction itself at 30 °C.
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Concentration Effects on Reaction Rate

In a reaction where the rate is dependent on the concentrations of reactants, changing the concentration of one reactant will affect the overall rate. If the concentration of methyl chloride is decreased, the rate of the reaction will also decrease proportionally, while the rate constant (k) will remain constant, as it is independent of reactant concentrations.
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