A2(g)+B2(g)⇌2AB(g)
Initial no. of moles 1 2 0
No. of moles
at equilibrium (1−x) (2−x) 2x
(Total vol=3 litre)
Active conc. (1−x)3 (2−x)3 2x3
Applying law of mass action
Kc=[AB]2[A2][B2]=(2x3)2((1−x)3)((2−x)3)=4x2(1−x)(2−x)
But,
4x2(1−x)(2−x)=50
or 23x2−75x+50=0
x=75±√752−4×23×502×23
x=2.317 or 0.943
The value of x cannot be more than 1 i.e., greater than the number of moles of A2 and hence x=0.943
No. of moles of AB=2x=(2×0.934)=1.868