In a particular temperature and time the rate of any reaction is proportional to the activation mass (Molar concentration and partial pressure) of the reactants present on that time. Activation mass means, the number of moles of substances dissolves in one liter solution.
Law of mass action can be explaining by reversible reaction.
The reaction, A + B ↔ C + D
According to mass action Law
The rate of forward reaction, r1 = K1 [A] * [B]
Here, [A] = The concentration of reactant of A
[B] = The concentration of reactant of B
K1 = Forward traction rate constant
Similarly, the rate of backward reaction, rb = K2 [C] x [D]
Here, [C] = Thc concentration of product of C
[D] = The concentration of product of D
K2 = Backward reaction rate constant
In equilibrium, r1 = rb
K1 [A] x [B] = K2 [C] x [D]
or, K1/ K2 = {[A] x [B]} / {[C] x [D]} = Kc
