1. In heterogeneous reactions, the surface area of the solid reactants play an important role in deciding the rate.
2. For a given mass of a reactant, when the particle size decreases surface area increases. Increase in surface area of reactant leads to more collisions per litre per second and hence the rate of reaction is increased.
3. For example, powdered calcium carbonate reacts much faster with dilute HCl than with the same mass of CaCO3 as marble.
