The enthalpy of ionization for sodium ion Na+ refers to the energy required to remove one electron from a neutral sodium atom Na to form a sodium ion Na+ . In this case, we are only concerned with the first ionization energy, as it represents the energy required to remove the first electron from the sodium atom.The first ionization energy of sodium Na is given as 495.8 kJ/mol. This value represents the enthalpy of ionization for sodium ion Na+ , as it is the energy required to remove one electron from a neutral sodium atom to form a sodium ion.Therefore, the enthalpy of ionization for sodium ion Na+ is 495.8 kJ/mol.