At a certain temperature, the degree of dissociation of ${\mathrm{PCl}}_5$ was found to be 0.25 under a total pressure of 15 atm. The value of ${\mathrm{K}}_{\mathrm{p}}$ for the dissociation of ${\mathrm{PCl}}_5$ in the reaction, ${\mathrm{PCl}}_5\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{PCl}}_3\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$

Initial moles of PCl₅ = 1

Degree of decomposition of PCl₅ = 0.25

Equilibrium presssure 15 atm

Moles of PCl₅ at equilibrium = (1 - 0.25) = 0.75

1 mole of PCl₅ gives 1 mole of PCl₃ and 1 mole of Cl₂

0.25 moles of PCl₅ gives _______ and _______.

Initial moles	1		-	-
Moles at equilibrium	(1 - 0.25)		0.25	0.25

Total moles at equilibrium = 1 - 0.25 + 0.25 +0.25 = 1.25