Practice question

Question

Given the following standard heats of formation, = 314. 6 kJ mol ⁻¹ 5.4 kJ mol ⁻¹ , and = 218. o kJ mol ⁻¹ , the average bond enthalpy of a P-H bond in PH ₃ (g) is kJ mol ⁻¹ (rounded off to one decimal place). (NAT)