How does increasing the surface area of a solid reactant influence the rate of a reaction?

How does increasing the surface area of a solid reactant influence the rate of a reaction?

• A. Surface area has no effect on rate.
• B. Larger surface area provides more collision sites, increasing rate.
• C. Larger surface area reduces rate.
• D. Surface area only affects final outcome, not rate.

Answer: (B)

Increasing surface area makes more of the solid reactant exposed to the other reactant, so more particles can collide per second. Reactions happen at the contact points between reactants, so when you grind a solid into powder, there are many more surface sites for collisions. That higher collision frequency speeds up the rate, even though the total amount of reactants is unchanged. So the rate goes up with larger surface area. The idea that surface area has no effect, or that it slows the reaction, or only changes the final amount, doesn't match what happens in practice because more exposed surface directly increases how often effective collisions occur.

Increasing surface area makes more of the solid reactant exposed to the other reactant, so more particles can collide per second. Reactions happen at the contact points between reactants, so when you grind a solid into powder, there are many more surface sites for collisions. That higher collision frequency speeds up the rate, even though the total amount of reactants is unchanged. So the rate goes up with larger surface area. The idea that surface area has no effect, or that it slows the reaction, or only changes the final amount, doesn't match what happens in practice because more exposed surface directly increases how often effective collisions occur.