LAW OF MASS ACTION.

• Rate of any chemical reaction at any instant, at a given temperature is directly proportional to the product of molar concentrations of reactants.
• It is the mathematical expression of the law of chemical equilibrium.

Suppose 'A' react with 'B' to produce 'C' and 'D' and reversely 'C' react with 'D' to produce 'A' and 'B'.
Velocity of forward reaction, say V1 and that of backward reaction, say V2.

Now according to the law of mass action:

 

 At equilibrium:

 

 

Here "K" is the measure of chemical affinity of the reactants. If "K" is large, A' and 'B' will show more tendency to produce 'C' and 'D' compared to the tendency of 'C' and 'D' to produce 'A' and ,B'. For highly
dissociable (ionizable) substance "K" value will be high and for less dissociable substance "K" value will
be low. "K" value of a particular reaction changes with temperature and it is definite for a given
chemical reaction at a given temperature.

 Importance of the law of mass action:

1. It explains the basis of biochemical reaction and predicts the reaction rate.
2. It expresses the concept of pH.
3. It explains the concept of solubility product of sparingly soluble salts in water.