Increasing surface area of a solid reactant tends to

• A. Increase the rate
• B. Decrease the rate
• C. Have no effect
• D. Change the mechanism

Answer: (A)

Increasing surface area exposes more of the solid to the other reactant, so collisions between reacting particles happen more often. For a solid reacting in a liquid or gas, only the surface particles can participate at any moment. By grinding a solid into a powder, you dramatically increase the number of particles at the surface, creating more reactive sites and raising the frequency of effective collisions. That higher collision rate makes the reaction proceed faster, so the rate increases.

This doesn’t change how the reaction proceeds step by step—the pathway stays the same—just more collisions occur per second. The other options don’t fit because decreasing surface area would slow the reaction, having no effect would ignore the extra contact, and changing the mechanism would require a different reaction pathway, which surface area alone doesn’t cause.