Rates can be monitored by volume of gas, eg. using a gas syringe/displacement of water from a measuring cylinder or by mass.
At the start conc, mass, SA of reactants id greatest.
When it begins to slow down it is cos conc of HCl/SA of CaCO3 has reduced as products form , so freq of collisions slows down causing rate to dec.
Reaction stops cos one of the reactants has ran out
Greater the SA the faster the reaction
Greater the temperature the faster the reaction
When a catalyst is added the speed inc