The enthalpy of formation of `CH_(4(g))` , at constant pressure is -76 kJ,at 300 K. What will be its enthalpy of formation at constant volume?

The enthalpy of formation of NaCl(s) is -411.2 kJ mol^(-1). The enthalpy of sublimation of Na(s), its ionization enthalpy in the gaseous state, the bond energy of chlorine, its electron gain enthalpy are 108.4, 495.6, 242 and -348.6 kJ mol^(-1) respectively. The energy required to break one mole of solid sodium chloride into its ions in the gaseous state is (in kJ)