Question

Phosphorus pentachloride decomposes according to the chemical equation. A 0.313 mol sample of PCl5(g) is injected into an empty 3.40 L reaction vessel held at 250 °C. Calculate the concentrations of PCl5(g) and PCl3(g) at equilibrium. KC=1.80 at 250 C

Answer 1

I am assuming this as the reaction, please check and reply in comment if the reaction is not correct

PCl5(g) ----- PCl3(g) + Cl2(g)

Molarity of PCl5 = number of moles of solute/Volume of solution (in L) = 0.313/3.40 = 0.09205

             PCl5(g) ----- PCl3(g) + Cl2(g)

Initial    0.09205        0             0

Final   (0.09205-x)     x            x

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

1.8 = x^2/(0.09205-x)

x = 0.087702M

Hence the concentration of PCl3 = 0.087702M

Concentration of PCl5 = 0.09205 - x = 0.09205 - 0.087702 = 0.004348M