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Chapter 14: Problem 13

On which of these quantities does the rate constant of a reaction depend: (a) concentrations of reactants, (b) nature of reactants, (c) temperature?

Short Answer

Expert verified
The rate constant of a reaction depends on the nature of reactants (Factor B) and temperature (Factor C). It does not, however, depend on concentrations of reactants (Factor A).

Step by step solution

01

Analysis of Factor A: Concentrations of Reactants

The rate constant is independent of the concentration of the reactants. This is due to the definition of rate constant, k in the rate law equation \(rate = k[A]^[n]\), where [A] is the concentration of reactant and n is the order. The rate of reaction changes with changing concentration, but not the rate constant.
02

Analysis of Factor B: Nature of Reactants

The nature of reactants definitely affects the rate constant. Different reactions featuring different reactants will have different rate constants. This is because their physical and chemical properties, including the energy landscape of the reaction and structural properties, would vary, resulting in differences for the rate constants.
03

Analysis of Factor C: Temperature

The rate constant, k, is also dependent on temperature. According to the Arrhenius equation, \(k = A \exp(-Ea/RT)\), where A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin. Therefore, as temperature increases, the rate constant also increases, assuming all other factors are held constant.

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Most popular questions from this chapter

What do we mean by the mechanism of a reaction?

What is the half-life of a compound if 75 percent of a given sample of the compound decomposes in 60 min? Assume first-order kinetics.

What is meant by the order of a reaction?

The following expression shows the dependence of the half-life of a reaction \(\left(t_{\frac{1}{2}}\right)\) on the initial reactant concentration \([\mathrm{A}]_{0}:\) $$ t_{\frac{1}{2}} \propto \frac{1}{[\mathrm{~A}]_{0}^{n-1}} $$ where \(n\) is the order of the reaction. Verify this dependence for zero-, first-, and second-order reactions.

A quantity of \(6 \mathrm{~g}\) of granulated \(\mathrm{Zn}\) is added to a solution of \(2 M \mathrm{HCl}\) in a beaker at room temperature. Hydrogen gas is generated. For each of the following changes (at constant volume of the acid) state whether the rate of hydrogen gas evolution will be increased, decreased, or unchanged: (a) \(6 \mathrm{~g}\) of powdered \(\mathrm{Zn}\) is used; \((\mathrm{b}) 4 \mathrm{~g}\) of granulated \(\mathrm{Zn}\) is used; \((\mathrm{c})\) \(2 M\) acetic acid is used instead of \(2 M \mathrm{HCl} ;\) d) temperature is raised to \(40^{\circ} \mathrm{C}\).
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