What happens to reaction rate if a solid reactant is ground into powder?

• A. Rate decreases due to less surface area.
• B. Rate increases due to more surface area.
• C. Rate remains the same.
• D. Reaction stops.

Answer: (B)

Increasing the surface area of a solid reactant exposes more particles to react with the other reactant, so there are more collisions at the reacting surface per unit time. Grinding the solid into powder greatly increases that exposed area, making the reaction occur more quickly. So the rate rises because more surface is available for the reaction to take place. Decreasing surface area would slow it, the rate wouldn’t stay the same, and grinding into powder doesn’t stop the reaction.