PCI5(g) <-> PCI3(g) + Cl2(g). At equilibrium, [PCl5] = 1 M and [Cl2] = 3.16x10^-2 M. What is the equilibrium concentration of PCl3? Use Keq=1x10^-3

Answer 1

PCl₅ <==> PCl₃ + Cl₂

Since PCl₃ and Cl₂ are produced in a 1:1 mol ratio, one would expect the concentrations to be the same, i.e. [PCl3] should also be 3.16x10^-2 M. We can verify this by using the equilibrium expression...

K = [PCl₃][Cl₂] / [PCl₅]

1x10^-3 = [PCl₃][3.16x10^-2] / [1]

[PCl₃] = 1x10^-3 / 3.16x10^-2

[PCl₃] = 3.16x10^-2 M