At a given temperature, the equilibrium constant for reaction
PCl5(g) ⇌ PCl3(g) + Cl2(g) is 2.4 × 10−3. At the same temperature, the
equilibrium constant for reaction PCl3(g) + Cl2(g ⇌ (PCl5(g) is
4.2 x 102
Reaction is reversed. Hence
K = 12.4 × 10−3 = 4.2 × 102