Concentration Equilibrium Constant
The equilibrium constant expressed in terms of the molar concentrations of the species involved.
Formula / equation
Kc = [C]^c[D]^d / [A]^a[B]^b
Unit
Various
In depth
Kc is the natural choice for reactions in solution and for gas reactions where concentrations are known. Pure solids and pure liquids are omitted from the expression because their concentrations are fixed by their densities and cannot change during the reaction.
Examples in the real world
For CaCO₃(s) ⇌ CaO(s) + CO₂(g), Kc is simply [CO₂] — the solids do not appear.