Question

1 moI of PCl₅, kept in a closed container of volume 1 dm³ and was allowed to attain equilibrium at 423 K. Calculate the equilibrium composition of reaction mixture. (The K_C value for PCl₅ dissociation at 423 K is 2)

Answer 1

PCl₅ ⇌ PCl₃ + Cl₂ 

Given that [PCl₅]_initail = 1 mol 

V = 1 dm³ 

K_C = 2

	PCl5	PCl3	Cl2
Initial no. of moles	1	-	-
No. of moles reacted	x	-	-
No. of moles at equilibrium	1 - x	x	x
Equilibrium concentration	(1 - x) / 1	x / 1	x / 1

∴ Equilibrium concentration of 

[PCl₅]_eq = (1 - x) / 1 = 1 – 0.732 = 0.268 M

[PCl₃]_eq = x / 1 = 0.732 / 1 = 0.732 

[Cl₂]_eq = x / 1= 0.732 / 1 = 0.732