Equilibrium in Chemical Processes

Decomposition of Calcium Carbonate

Calcium carbonate when heated to 1073K in a closed evacuated vessel, starts decomposing to yield calcium oxide and carbon dioxide gas. Carbon dioxide builds up pressure within the vessel which can be recorded on a manometer. The pressure goes on increasing as the reaction proceeds and finally becomes constant. It appears as if the reaction has come to a stop although CaCO₃ is still present. This indicates that the system has attained the equilibrium state.

At equilibrium, rate of forward reaction i.e.

CaCO₃   →  CaO  +   CO₂

becomes equal to rate of  backward reaction i.e.

CaO   +   CO₂  →  CaCO₃

CaCO₃     ↔   CaO  +  CO₂