Why does not the equilibrium constant expression for a reaction involving pure solids or liquid contain the concentrations terms of the solid or liquids?

Explanation

For a pure solid or liquid, the molar concentration is directly proportional to density. As the density is constant at a given temperature therefore, for a pure solid or liquid at a constant temperature, the molar concentration is a constant quantity, which is usually taken as unity (1). for this reaction, the equilibrium constant expression for a reaction involving pure solids or liquids does not contain concentration terms of the solids or liquids.