In a homogeneous system, all the reactants and products are in the same phase. Equilibrium in a system having more than one phase is called heterogeneous equilibrium. The equilibrium between water vapour and liquid water in a closed container is an example of heterogeneous equilibrium.Heterogeneous equilibrium involves pure solids or liquids.

The molar concentration of a pure solid is constant

The molar concentration of a pure liquid is constant independent of  the amount present.

Thermal dissociation of calcium carbonate is an example of heterogeneous chemical equilibrium.[CaCO3(s)] and [CaO(s)] are both constant

n/V is concentration expressed in mol/m3

Identification of type of equilibrium