A 2.500-mol sample of phosphorus pentachloride, PCl₅, decomposes at 160°C and 1.00 atm to give 0.338 mol of phosphorus trichloride, PCl₃, at equilibrium.
PCl₅(g) ⇌ PCl₃(g) + Cl₂(g)
What is the composition of the final reaction mixture?