Reaction rate factors for heterogeneous reactions

Steps:

• Reaction rate increases with higher reactant concentration, greater surface area of solids, and elevated temperature.
• Option A raises HCl concentration, increasing collision frequency.
• Option B enlarges particle size, reducing exposed surface area for collisions.
• Option C boosts surface area directly, enhancing contact between reactants.
• Option D elevates temperature, increasing molecular kinetic energy and collisions.

Why B is correct:

• Larger particles decrease surface area, reducing effective collisions per collision theory, slowing the rate.

Why the others are wrong:

• A: Higher concentration increases reactant molecules, accelerating the reaction.
• C: Greater surface area exposes more CaCO3 sites, speeding up the reaction.
• D: Higher temperature boosts particle speed, increasing collision effectiveness.

Final answer: B