The mean bond enthalpy of a P-Cl bond is 331 kJ mol^-1 and of a Cl-Cl bond is 242 kJ mol^-at 298 K. If the mean standard enthalpy of atomization of white phosphorus is 315 kJ mol^-1, estimate the standard enthalpy of formation of gaseous phosphorus trichloride, PCl₃, at this temperature.

Question

Quizplus · Accepted Answer

The standard enthalpy of formation of PCl3 can be calculated using bond enthalpies. The formation of PCl3 involves breaking three P-Cl bonds and one and a half Cl-Cl bonds, and forming one P4 bond (as a quarter of P4 is used). The calculation is as follows: ΔHf° = (3 * 331 kJ/mol + 1.5 * 242 kJ/mol) - 315 kJ/mol = -315 kJ/mol. This calculation considers the energy required to break the bonds in the reactants and the energy released by forming the bonds in the products, leading to the conclusion that option A is correct.

The Mean Bond Enthalpy of a P-Cl Bond Is 331