Law of Chemical equilibrium or equilibrium constant:-

Let us consider the reaction

Rate of forward reaction = Kf[A][B]

Rate of backward reaction = K_B[C][D]

At equilibrium

Rate of forward reaction = Rate of backward reaction

K_f [A][B] = K_B [C][D]

Hence, equilibrium constant may be defined as ratio b/w the product of molar concentration of the product to that the molar concentration of the reactant with each concentration term raised to a power equal to numerical coefficient in the balanced chemical equation & expression is known as law of chemical equilibrium:

Equilibrium constant:

Equilibrium constant in gaseous system:

The concentration of gases may also be expressed in terms of their partial pressure

PV=nRT

P_A = C_A.RT

P_B = C_B.RT

P_C = C_C.RT

P_D = C_D.RT

K_P = K_C RT^(c+d)-(a+b)

K_P = K_C (RT)^Δng