1. what is law of mass action?

2.Explain law of chemical equilibrium and derive it.

1)Law of Mass action :  This law was given by Guldberg and Waage in 1864. It states that- The rate of reaction is proportional to the product of the active masses of the reactants , each raised to the power to its stoichiometric coefficient as represented by the balanced reaction.
2)Law of chemical equilibrium : It states that- The product of the molar concentration of the products, each raised to the power equal to its stoichiometric coefficient divided by the product of the molar concentrations of the reactants , each raised to the power equal to its stoichiometric coefficient is constant at constant temperature and is called  Equilibrium constant.
DERIVATION:
consider the general reversible reaction:
A + B $\leftrightarrow$ C + D
At equilibrium , suppose  the active masses of A, B, C, and D are represented as [A], [B], [C] and [D].
 Applying the law of mass action-
Rate at which A and B react together , that is , Rate of forward reaction $\alpha$ [A][B]
= K_f [A][B]
where  K_f is proportionality constant is called as velocity constant for forward reaction.
Similarly, rate at which C and D react together ,that is, Rate of the backward reaction
= K_b[C][D]
where K_b represents the velocity constant for the backward reaction
At equilibrium,
Rate of forward reaction=  Rate of the backward reaction
K_f[A][B]= K_b[C][D]
$\frac{K_f}{K_b}=\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}$
K=  $\frac{\left[C\right]\left[D\right]}{\left[A\right]\left[B\right]}$
Where K is Equilibrium Constant