Question

The rate constant \((k)\) depends on which of the following (there may be more than one answer)? a. the concentration of the reactants b. the nature of the reactants c. the temperature d. the order of the reaction Explain.

Short answer

The rate constant (k) depends on the nature of the reactants (option b) and the temperature (option c). The concentration of the reactants (option a) and the order of the reaction (option d) do not affect the rate constant.

Step-by-step solution

Option a: the concentration of the reactants

The rate constant does not depend on the concentration of the reactants. The rate constant best describes the inherent speed of a reaction, and while the overall reaction rate is affected by the concentration, the rate constant remains constant for a specific reaction at a specific temperature. So, this option is incorrect.

Option b: the nature of the reactants

The nature of the reactants plays a significant role in determining the rate constant. Different reactants have their own distinct reactivity depending on their molecular structure, bonding, and other factors. A reaction with more reactive species would have a higher rate constant. Therefore, this option is correct.

Option c: the temperature

Temperature affects the rate constant through the Arrhenius equation, which states that the rate constant is proportional to the exponential of the activation energy divided by the product of the gas constant and the temperature: \[k = A\exp\left(-\frac{E_a}{R}\cdot \frac{1}{T}\right)\] where \(A\) is the pre-exponential factor, \(E_a\) is the activation energy, \(R\) is the gas constant, and \(T\) is the temperature in Kelvin. As the temperature increases, the rate constant increases as well, and vice versa. Therefore, this option is correct.

Option d: the order of the reaction

The order of the reaction (n) indicates how the rate of the reaction depends on the concentration of the reactants: \[\text{rate} = k[\text{reactants}]^n\] The rate constant itself does not depend on the order of the reaction. It is simply a proportionality constant that links the concentration of the reactants to the rate of the reaction. Therefore, this option is incorrect. To summarize, the rate constant depends on the nature of the reactants (option b) and the temperature (option c).