The enthalpy change of ionization, also known as ionization energy, is the energy required to remove an electron from an atom or ion in its gaseous state. In this case, the enthalpy change of ionization for magnesium is given as 125 kJ/mol for the removal of one electron from a magnesium atom.The ionization process can be represented as:Mg g Mg g + eThe enthalpy change of ionization for this process is 125 kJ/mol.