Born–Haber cycle

Born–Haber cycles are used primarily as a means of calculating lattice energy (or more precisely enthalpy[note 1]), which cannot otherwise be measured directly.

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).

Most compounds include covalent and ionic contributions to chemical bonding and to the lattice energy, which is represented by an extended Born–Haber thermodynamic cycle.

The enthalpy of formation of lithium fluoride (LiF) from its elements in their standard states (Li(s) and F2(g)) is modeled in five steps in the diagram: The sum of the energies for each step of the process must equal the enthalpy of formation of lithium fluoride,

[6] The word cycle refers to the fact that one can also equate to zero the total enthalpy change for a cyclic process, starting and ending with LiF(s) in the example.

Born–Haber cycle for the standard enthalpy change of formation of lithium fluoride . ΔH latt corresponds to U L in the text. The downward arrow "electron affinity" shows the negative quantity –EA F , since EA F is usually defined as positive.