Question

Phosphorus pentachloride decomposes according to the chemical equation PCl5(g) <======> PCl3(g) and PCl2(g)

Kc=1.8

A 0.327 mol sample of PCl5(g) is injected into an empty 4.10 L reaction vessel held at 250 °C. Calculate the concentrations of PCl5(g) and PCl3(g) at equilibrium.

PCl5=

PCl3=

Answer 1

molarity of PCl5 = moles / volume = 0.327 / 4.10 = 0.0798 M

PCl5 <-----------------------> PC3 + Cl2

0.0798                               0          0

0.0798-x                            x           x

Kc = [PCl3][Cl2]/[PCl5]

Kc = x^2 / 0.0798 -x

1.8 = x^2 / 0.0798 -x

x^2 + 1.8 x -0.144 = 0

x = 0.0767

equilibrium concentrations:

[PCl5] = 0.0798 - x = 0.0798 - 0.0767 = 0.0031 M

[PCl3]   = x   = 0.0767 M