(1) A chemical reaction takes place due to collisions of the reactant molecules. Higher the concentrations of the reactants more will be the frequency of collisions and faster wifi be the rate of the reaction.
(2) In the reaction of dil. HCI and CaCO3, CaCO3 disappears slowly and CO2 also liberates slowly. On the other hand the reaction with concentrated HCI takes place rapidly and CaCO3 disappears fast.
(3) Concentrated acid reacts faster than dilute acid, that means the rate of a reaction is proportional to the concentration of reactants.
Slow reaction:
CaCO3 + dil.2HCl → CaCl2 + CO2 + H2O
Fast reaction:
