kilo equilibrium constant Quantity characterizing the equilibrium of a chemical reaction and defined by an expression of the type , where is the stoichiometric number of a reactant (negative) or product (positive) for the reaction and stands for a quantity which can be the equilibrium value either of pressure, fugacity, amount concentration, amount fraction, molality, relative activity or reciprocal absolute activity defining the pressure based, fugacity based, concentration based, amount fraction based, molality based, relative activity based or standard equilibrium constant (then denoted ), respectively.

Solids and liquids, as long as there is some available, are fully available to the reaction in a macroscopic amount that does not limit the reaction.

This is different from a solution of a certain molarity or a gas of a certain pressure. The sparseness of solutes or gases means that the availability is limited by the concentration or the pressure. For solids and liquids, the availability is considered constant as long as some macroscopic amount is present.