Chemistry assignment 9

Question

Phosphorus pentachloride decomposes according to the chemical equation PCl5(g)↽−−⇀PCl3(g)+Cl2(g)𝐾c=1.80 at 250 ∘C A 0.2850 mol sample of PCl5(g) is injected into an empty 2.95 L reaction vessel held at 250 ∘C. Calculate the concentrations of PCl5(g) and PCl3(g) at equilibrium.

Answer 1

PCl₅(g) <==> PCl₃(g) + Cl₂(g) ... Kc = 1.80

[PCl₅] = 0.2850 mol / 2.95 L = 0.0966 M

Set up an ICE table:

PCl₅(g) <==> PCl₃(g) + Cl₂(g)

0.0966...............0..............0...............Initial

-x..................+x.............+x.............Change

0.0966-x.............x...............x.............Equilbrium

Plug values into the equilibrium expression and solve for x:

1.80 = (x)(x) / 0.0966-x)

1.80 = x² / 0.0966-x

x² = 0.1734 - 1.80x

x² + 1.80x - 0.1734 = 0

x = 0.0917

At equilibrium, [PCl₅] = 0.0966 - x = 0.0966 - 0.0917 = 0.0049 M

At equilibrium, [Cl₂] = x = 0.0917 M