The constant KC is called the equilibrium constant and applies to reactions in solution. It contains only concentration terms. It should not included terms for (1) any pure solid (ii) any pure liquid, unless it is a reactant or product liquid, unless it is a reactant or product of the reaction or (iii) any solvent.
The equilibrium constant is a true constant for it given reaction. It value does not depend for a given reaction. It value does not depend on the initial concentration of the reactants or products. The values of the equilibrium constant does, however, vary with temperature for that the equilibrium constant never be zero or infinity.
