Question

Phosphorus pentachloride decomposes according to the chemical equation. A 0.153 mol sample of PCl5(g) is injected into an empty 2.30 L reaction vessel held at 250 °C. Calculate the concentrations of PCl5(g) and PCl3(g) at equilibrium. kc=1.80@250 degrees celsius

Answer 1

The reaction should be PCl5(g) <------> PCl3(g) + Cl2(g)

The initial concentration of PCl5 is 0.153/ 2.3 = 0.066521 mol/L (M)

Initial condtions:
[PCl5] = 0.066521M
[PCl3] = 0
[Cl2] = 0

Change if x amount of PCl5 dissociates
∆[PCl5] = -x
∆[PCl3] = +x
∆[Cl2] = +x

Equiiibrium
[PCl5] = 0.066521 - x
[PCl3] = x
[Cl2] = x

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

1.80 = x²/(0.066521 - x)
x = 0.064229

[[PCl5] = 0.066521 - x = 0.0022948 mol/L
[PCl3] = x = 0.064229 M
[Cl2] = x = 0.064229 M