# Why are solids and liquids ignored in the equilibrium constant?

If a reaction is taking place and is going towards equilibrium, wouldn’t the reactant be consumed to form products and vice versa? If this reactant/product is a solid or liquid, wouldn’t the number of moles when the reaction reaches equilibrium decrease/increase from its initial number of moles? Wouldn’t this change in moles from start of reaction to point of equilibrium be important to the equation, since it’s a ratio of products to reactants at equilibrium?

• Well there isn't quite enough information to answer the question. A specific problem would allow a precise answer. However, in general, products in another phase don't appear in the equilibrium expression. So in a solution, gaseous or solid products wouldn't be used in the equilibrium expression.
– MaxW
Oct 25 '18 at 4:35