The equilibrium constant Kc in chemistry or Keq indicates the ratio of the concentration of all substances involved in a chemical equilibrium reaction. It is used in particular in connection with the law of mass action. That is why it is often referred to as the mass action constant, more rarely as the equilibrium constant. In contrast to the position of the equilibrium, the value of the equilibrium constant depends only on the temperature and not on the concentration or the pressure.
For any reversible reaction at equilibrium, the ratio of products to reactants at a certain temperature will always equal a constant, Kc
Kc= Concentration of products/ Concentration of reactants
Specifically, for any reversible reaction at equilibrium
aA + bB ⇄ cC + dD
The equilibrium constant, Keq Or KC, is
Kc = [C]c [D]d / [A]a [B]b