In which of the following situations does the rate of a chemical reaction increase?

• A. Decreasing the temperature
• B. Adding a non-reactive gas at constant volume
• C. Increasing the concentration of reactants
• D. Lowering the surface area of a solid reactant

Answer: (C)

Verified step by step guidance

1. Understand that the rate of a chemical reaction generally depends on factors such as temperature, concentration of reactants, surface area, and presence of catalysts.
2. Recall that increasing temperature usually increases reaction rate because particles have more kinetic energy, leading to more frequent and energetic collisions; therefore, decreasing temperature would decrease the rate.
3. Consider the effect of adding a non-reactive gas at constant volume: since the volume does not change, the partial pressures (or concentrations) of the reactants remain the same, so the reaction rate does not increase.
4. Recognize that increasing the concentration of reactants increases the frequency of collisions between reactant molecules, which typically increases the reaction rate.
5. Note that lowering the surface area of a solid reactant reduces the available area for collisions, thus decreasing the reaction rate rather than increasing it.