Q.Explain homogeneous and heterogeneous equilibria.

Chemical equilibria fall into two classes depending on how many physical phases the reactants and products are spread across.

In a homogeneous equilibrium, every reactant and every product sits in the very same phase. $H_2(g)+I_2(g)\rightleftharpoons 2HI(g)$ is homogeneous because all three species are gases; the ester-hydrolysis equilibrium $CH_3COOCH_3(aq)+H_2O(aq)\rightleftharpoons CH_3COOH(aq)+CH_3OH(aq)$ is homogeneous too, with all four species dissolved in one aqueous phase -- homogeneous equilibrium is not restricted to gases, only to one shared phase, whichever phase that happens to be.

In a heterogeneous equilibrium, the reactants and products span more than one phase. The liquid-vapour equilibrium $H_2O(l)\rightleftharpoons H_2O(g)$ spans a liquid and a gas phase; the thermal decomposition $CaCO_3(s)\rightleftharpoons CaO(s)+CO_2(g)$ spans two solid phases and a gas phase. …