Question

Determine the equilibrium constant, Kgoal, for the reaction 4PCl5(g)⇌P4(s)+10Cl2(g),    Kgoal=?   by making use of the following information:

P4(s)+6Cl2(g)⇌4PCl3(g),       K1=2.00×1019

PCl5(g)⇌PCl3(g)+Cl2(g),       K2=1.13×10−2

Answer 1

4PCl5(g)⇌P4(s)+10Cl2(g),    Kgoal=

PCl5(g)⇌PCl3(g)+Cl2(g),       K₂=1.13×10⁻²   ---------- (1)

4PCl3(g)⇌P4(s)+6Cl2(g),     K^'₁ = 1/K₁ = 1/(2.00x10¹⁹) = 5.00x10^-20 ---------- (2)

Multifply equation (1) with 4 then

4PCl5(g)⇌4PCl3(g)+4Cl2(g),      K^'₂= (K₂)⁴= (1.13×10⁻² )⁴ = 1.63x10^-8 --------- (3)

On multiplying K'₁ and K'₂

K_goal = K'₁ * K'₂ = 5.00x10^-20 x 1.63x10^-8 = 8.15236 x 10^-28