A mixture of reactants and products in the equilibrium state is called an equilibrium mixture.Norwegian chemists Cato Maximillian Guldberg and Peter Waage proposed in 1864 that the concentrations in an equilibrium mixture are related by an equilibrium equation.The equilibrium equation is also known as the law of mass action.

 

The Equilibrium Law or Law of Chemical Equilibrium states that At a given temperature, the product of concentrations of the reaction products raised to the respective stoichiometric coefficient in the balanced chemical equation divided by the product of concentrations of the reactants raised to their individual stoichiometric coefficients has a constant value the Equilibrium Law or Law of Chemical Equilibrium.

Equilibrium constant expression for the general reaction representation about A + B ⇋ C + D

K=[C][D]/ [A][B]

Equilibrium constant expression for the general reaction representation about aA +bB ⇋cC +dD

K=[C]c[D]d/ [A]a[B]b

Characteristics of Equilibrium Constant

• The equilibrium constant has a constant value for a particular reaction at a particular temperature.
• The equilibrium constant has a relation with equilibrium concentration and not with initial concentration.
• The equilibrium constant for the reverse reaction is the inverse of the equilibrium constant for the reaction in the forward direction.
• The value of equilibrium constant is unaffected by the addition of catalyst.