Which of the following changes would decrease the rate of a chemical reaction?

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

Answer: (A)

Verified step by step guidance

1. Understand that the rate of a chemical reaction depends on factors such as temperature, presence of a catalyst, surface area of reactants, and concentration of reactants.
2. Recall that increasing temperature generally increases reaction rate because particles have more kinetic energy, leading to more frequent and energetic collisions.
3. Know that adding a catalyst lowers the activation energy, which increases the reaction rate by allowing more collisions to result in a reaction.
4. Recognize that increasing the surface area of a solid reactant exposes more particles to react, increasing the frequency of collisions and thus the reaction rate.
5. Understand that increasing the concentration of reactants increases the number of particles in a given volume, leading to more collisions and a faster reaction rate; therefore, lowering the temperature is the only change listed that decreases the reaction rate.