The reaction of 1.00 mol of solid phosphorus with chlorine gas to form PCl3 (g) releases 287.0 kJ of heat energy.The reaction of 1 .00 mol of solid phosphorus with chlorine gas to form PCl5 (g) releases 374.9 kJ of heat energy.Using Hess's Law , indirectly calculate the enthalpy change for : PCl3 (g) + Cl2 (g) > PCl5(g)