Surface Area's Impact on Reaction Rate

Steps:

• Assume graphs P and Q depict concentration vs. time for a solid-acid reaction, with P showing faster initial rate and Q slower, both reaching the same endpoint.
• Recall that reaction rate depends on collision frequency, influenced by surface area for heterogeneous reactions.
• Smaller solid pieces increase exposed surface area, accelerating the rate for P compared to standard conditions.
• Larger solid pieces reduce surface area, slowing the rate for Q.

Why C is correct:

• Smaller particles increase surface area, raising effective collision frequency per collision theory, yielding faster initial rate; larger pieces do the opposite.

Why the others are wrong:

• A: Both changes (higher concentration and smaller pieces) increase rate, so neither produces a slower Q.
• B: Higher temperature increases rate for P, but more dilute acid also slows Q—however, volume specification mismatches typical surface area effects on solids.
• D: Catalyst speeds up P without changing equilibrium, but lower temperature slows Q; this ignores solid particle size's direct surface area role.

Final answer: C