How does reducing the temperature of a chemical reaction affect the rate at which it occurs?

• A. It causes the reaction rate to remain constant regardless of temperature.
• B. It increases the reaction rate by providing more energy for collisions.
• C. It decreases the reaction rate by lowering the kinetic energy of the reactant molecules.
• D. It has no effect on the reaction rate.

Answer: (C)

Verified step by step guidance

1. Understand that the rate of a chemical reaction depends on the frequency and energy of collisions between reactant molecules.
2. Recall that temperature is directly related to the average kinetic energy of molecules; higher temperature means higher kinetic energy.
3. Recognize that when temperature decreases, the kinetic energy of reactant molecules decreases, leading to fewer molecules having enough energy to overcome the activation energy barrier.
4. Apply the Arrhenius equation, which shows that the reaction rate constant k depends on temperature T as \(k = A e^{-\frac{E_a}{RT}}\), where \(E_a\) is activation energy, \(R\) is the gas constant, and \(A\) is the frequency factor.
5. Conclude that lowering temperature decreases the rate constant k, thus decreasing the reaction rate because fewer effective collisions occur.