How does surface area affect reaction rate?

• A. A larger surface area increases the rate by allowing more collisions.
• B. A larger surface area decreases the rate.
• C. Surface area has no effect on rate.
• D. Surface area only affects gas-phase reactions.

Answer: (A)

The main idea is that reaction rate depends on how often reacting particles collide and react. When a solid is broken into smaller pieces or ground into powder, its surface area increases, exposing more particles to the other reactant. This means collisions between particles happen more often per second, so the reaction proceeds faster. The energy of each collision isn’t what changes with surface area; it’s the increased frequency of effective collisions that speeds things up. This effect isn’t limited to gases—solid reacts with liquids or gases also respond to larger surface area. So, increasing surface area speeds up the rate, rather than decreasing it or having no effect.