The lattice energy of NaCl is -780 kJ mol^-1 .The enthalpies of hydration of (g ) ${{\mathrm{Na}}_{\left(\mathrm{g}\right)}^{+}}_{ }$ and ${\mathrm{Cl}}_{\left(\mathrm{g}\right)}^{-}$ are -406 kJ mol^- and -364 kJ mol^-1 .The enthalpy of solution of NaCl(s) is