Concept:Surface area affects reactions that involve a solid reactant.
Explanation:Only reaction A contains a solid reactant,
CaCO3.
Powdering or breaking
CaCO3 increases its surface area.
This exposes more particles to
HCl, increasing effective collisions.
Hence, the reaction rate increases when surface area is increased.
Options B, C and D involve aqueous or gaseous reactants, where surface area has little effect.
Answer:A.
CaCO3+2HCl→CaCl2+H2O+CO2