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Question

Phosphorus pentachloride decomposes according to the chemical equation

A  sample of  is injected into an empty  reaction vessel held at 

Calculate the concentrations of  and  at equilibrium.

Answer 1

Concentration of PCl₅ initially = 0.2215 mol/2.80 L = 0.0791 M

PCl₅(g) ===> PCl₃(g) + Cl₂(g)

0.0791.............0..............0..........Initial

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

0.0791-x...........x.............x.........Equilibrium

Kc = 1.80 = [PCl₃][Cl₂]/[PCl₅]

1.80 = (x)(x)/0.0791 - x

0.142 - 1.80x = x²

x² + 1.80x -0.142 = 0

x = 0.076 M

At equilibrium...

[PCl₅] = 0.0791 - 0.076 = 0.0031 M

[PCl₃] = 0.076 M