4 mole of PCl₅ and 2 mole of Cl₂ are heated in a 2L vessel to establish an equilibrium $\left[{\mathrm{PCl}}_5\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{PCl}}_3\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)\right].$ Equilibrium molar concentration of PCl₃ is 1. Then the value of K_c for the above equilibrium is