The energy required to remove one or more electrons to make a cation is a sum of successive ionization energies for example, the energy needed to form Mg 2+ is the ionization energy required to remove the first electron from Mg, plus the ionization energy required to remove the second electron from Mg +. If the element is normally a molecule then we first have to consider its bond dissociation enthalpy (see also bond energy). To make gaseous ions from elements it is necessary to atomise the elements (turn each into gaseous atoms) and then to ionise the atoms. A Born–Haber cycle applies Hess's law to calculate the lattice enthalpy by comparing the standard enthalpy change of formation of the ionic compound (from the elements) to the enthalpy required to make gaseous ions from the elements. The lattice enthalpy is the enthalpy change involved in the formation of an ionic compound from gaseous ions (an exothermic process), or sometimes defined as the energy to break the ionic compound into gaseous ions (an endothermic process). The cycle is concerned with the formation of an ionic compound from the reaction of a metal (often a Group I or Group II element) with a halogen or other non-metallic element such as oxygen.īorn–Haber cycles are used primarily as a means of calculating lattice energy (or more precisely enthalpy ), which cannot otherwise be measured directly. It was also independently formulated by Kasimir Fajans and published concurrently in the same issue of the same journal. It was named after the two German scientists Max Born and Fritz Haber, who developed it in 1919. The Born–Haber cycle is an approach to analyze reaction energies.
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