For the dissociation reaction N2O4(g)⇌2NO2(g), the degree of dissociation (α) in terms of Kp and total equilibrium pressure P is :
N2O4(g)NX2OX4(g) say initially is P atmP atm.
Now we have:
Considering initial pressure of N2O4 as p, at equilibrium, assuming 'x' as the degree of dissociation, we will have pressure of N2O4 to be p(1-x) and pressure of NO2 as 2px.
So,
assuming 1−x1−x approximately as 11,