Increasing the surface area of reactants generally has what effect on reaction rate?

• A. Increase rate.
• B. Decrease rate.
• C. No effect.
• D. Change equilibrium constant.

Answer: (A)

Increasing the surface area of reactants speeds up the reaction because more surface sites are exposed for collisions between reacting species. In reactions where a solid reactant meets other reactants in a medium, only particles at the surface can collide and react. By breaking a solid into smaller pieces or grinding it into a powder, you expose more surface area, leading to more frequent effective collisions and a faster rate of product formation. The equilibrium constant, on the other hand, depends on temperature and the thermodynamics of the reaction, not on how fast the reaction proceeds, so changing surface area changes the rate but not the position of equilibrium. So, increasing surface area generally increases the rate.