Born–Haber Cycle
A thermochemical cycle applying Hess's law to determine the lattice energy of an ionic compound indirectly.
Formula / equation
ΔH_f = ΔH_sub + IE + ½D + EA + U
Unit
kJ/mol
In depth
The cycle breaks formation of the solid from its elements into measurable steps: atomisation, ionisation, bond dissociation, electron affinity and lattice formation. Since every other term can be measured, the lattice energy follows by difference. Disagreement with the calculated ionic value reveals covalent character.
Examples in the real world
The cycle for NaCl combines +107, +496, +122 and −349 kJ/mol with ΔH_f = −411 to give U = −787 kJ/mol.