TASC Physical Science Practice Exam

The rate of a reaction depends on how often reacting particles meet, and for reactions involving a solid and another reactant, only the particles at the solid’s surface can participate. Increasing the surface area of the solid means more of its particles are exposed to the other reactant, producing more collisions per unit time and speeding up the reaction. That’s why breaking a solid into smaller pieces or grinding it into a powder often makes a reaction go faster—the surface area goes up a lot, so contact and collision opportunities increase. The other statements don’t fit because temperature changes usually speed up reactions when you raise it, not slow them; increasing the container volume lowers the concentration of reactants and tends to slow the rate; and a catalyst provides an alternative pathway that speeds up the reaction, not slows it.