Which of the following changes will decrease the number of effective collisions during a chemical reaction?

• A. Increasing the surface area of a solid reactant
• B. Lowering the temperature of the reaction mixture
• C. Increasing the concentration of reactants
• D. Adding a catalyst to the reaction

Answer: (B)

Verified step by step guidance

1. Understand that the number of effective collisions in a chemical reaction depends on factors such as temperature, concentration, surface area, and presence of a catalyst, all of which influence how often and how energetically molecules collide.
2. Recall that increasing the surface area of a solid reactant generally increases the number of effective collisions because more reactant particles are exposed and available to collide.
3. Recognize that increasing the concentration of reactants increases the frequency of collisions, thus increasing the number of effective collisions.
4. Know that adding a catalyst provides an alternative reaction pathway with a lower activation energy, which increases the number of effective collisions without being consumed in the reaction.
5. Understand that lowering the temperature decreases the kinetic energy of molecules, reducing both the frequency and energy of collisions, which leads to a decrease in the number of effective collisions.