Pulverizing a solid reactant into a fine powder makes its reaction with a solution proceed faster chiefly because:

Core Concept

Grinding splits one chunk into many small particles, multiplying the exposed area where solution particles can attack. Reaction can occur only at the surface, so more available surface raises the number of effective collisions per second. Neither the activation energy nor the rate constant changes. Concentrations are likewise untouched; only the accessible interface grows.