Question

Explain why pure liquids and solids can be ignored while writing the equilibrium constant expression?

Answer 1

The concentration of solid or liquid is $\frac{\text{Number of moles}}{\text{volume in L}}$$=\frac{\text{Mass}}{\text{Volume}\times \text{molar mass}}$$=\frac{\text{Density}}{\text{Molar mass}}$.
At constant temperature, the density and molar mass of pure solid and liquid are constant.
Due to this, their molar concentrations are constant and are not included in the equilibrium constant.