Question

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

Answer 1

For a pure substance (both solids and liquids),
[Pure substance]$=\frac{Numberofmoles}{Volume}=\frac{Mass/molecularmass}{Volume}=\frac{Mass}{Volume\times Molecularmass}=\frac{Density}{Molecularmass}$
Now, the molecular mass and density (at a particular temperature) of a pure substance is always fixed and is accounted for in the equilibrium constant. Therefore, the values of pure substances are not mentioned in the equilibrium constant expression.