Four moles of PCl5 are heated in a closed 4dm3 container to reach equilibrium at 400K. At equilibrium, 50% of PCl5 is dissociated. What is the value of Kc for the dissociation of PCl5 into PCl3 and Cl2 at 400K?

PCl5⇌PCl3+Cl2 No of moles of PCl5 dissociated = 50% of 4 moles                                                         = 2 molesAmount at equilibriumPCl5=4−2=2moles PCl3=2moles =24=0.5 Cl2=2moles =24=0.5 Kc=0.5×0.50.5=0.5  M/L