Question

1. a decrease in temperature will decrease the rate of a reaction principally because

a. the particles have less kinetic energy at the lower temperature

b. the particles in the reactants move further apart at a lower temperature

c. the potential energy for the reaction increases with a decrease in temperature

d. the activation energy of the reaction decreases with a decrease in temperature

e. more particles have energy less than the activation energy

Explanation:

To determine the correct answer, we analyze each option:

• Option a: Particles in reactants moving apart isn't the main reason for reaction rate decrease with temperature drop. The key is kinetic energy and activation energy, not distance between particles. Eliminate a.
• Option b: The potential energy of the reaction (related to enthalpy) doesn't increase with lower temperature. Temperature affects kinetic energy, not potential energy of the reaction. Eliminate b.
• Option c: The activation energy of a reaction is a constant for a given reaction (it's the energy barrier that reactants must overcome to form products). It doesn't change with temperature. So this is incorrect. Eliminate c.
• Option d: The activity of a catalyst can be affected by temperature, but the question is about the principal reason for the reaction rate decrease with temperature, which is related to the kinetic energy of reactant particles and their ability to overcome the activation energy. Catalyst activity change is not the principal reason here. Eliminate d.
• Option e: According to the kinetic molecular theory, the kinetic energy of particles is related to temperature (average kinetic energy is proportional to absolute temperature). When temperature decreases, the average kinetic energy of reactant particles decreases. So, more particles will have energy less than the activation energy (the minimum energy required for a reaction to occur). Fewer particles will have enough energy to overcome the activation energy, leading to a decrease in the reaction rate. This explains the principal reason for the rate decrease.

Answer:

e. More particles have energy less than the activation energy