Question

Given that- 2 CCl4(g) + O2(g) ⇌ 2 COCl2(g) + 2 Cl2(g) has Kc = 9.9 x 1051
What is Kc for the following equilibrium: COCl2(g) + Cl2(g) ⇌ CCl4(g) + ½ O2(g) ?
A) 9.9 x 10–51 B) 5.0 x 10–53 C) 1.0 x 10–26
D) 1.0 x 10–52 E) –9.9 x 1051

Answer 1

2 CCl4(g) + O2(g) ⇌ 2 COCl2(g) + 2 Cl2(g)

Kc1 = [COCl2]^2 * [Cl2]^2 / [O2]*[CCl4]^2 = 9.9*10^51     ......................... (1)

now,

for COCl2(g) + Cl2(g) ⇌ CCl4(g) + ½ O2(g)

Kc2 = [CCl4]*[O2]^0.5 / [COCl2] *[Cl2]

squaring on both sides,

(Kc2)^ 2 = [O2]*[CCl4]^2 / [COCl2]^2 * [Cl2]^2

               = 1/Kc1       ................................... from (1)

so

Kc2 = 1.0 *10^-26    . .......................... answer is option C