Is this problem missing something i.e. temperature or am I just not understanding how to work it?
A 0.72 mol sample of PCl5 is put into a 1.00 L vessel and heated. At equilibrium the vessel contains 0.40 mol of PCl3 (g) as well as Cl2(g) and undissociated PCL5(g). What is the equilibrium constant for the decomposition of PCl5 to PCl3 and Cl2 at this temperature.