Born-Haber cycle is a cycle of reactions used for calculating the lattice energies of ionic crystalline solids. For a compound MX, the lattice energy is the enthalpy of the reaction M+(g) + X-(g) → M+X-(s) ΔHL The standard enthalpy of formation of the ionic solid is the enthalpy of the reaction M(s) + 1/2X2(g) → M+X-(s) ΔHf The cycle involves equating this enthalpy (which can be measured) to the sum of the enthalpies of a number of steps proceeding from the elements to the ionic solid. The steps are: 1) Atomization of the metal M(s) → M(g) ΔH1 2) Atomization of the nonmetal 1/2X2(g) → X(g) ΔH2 3) Ionization of the metal M(g) → M+(g) + e- ΔH3 This is obtained from the ionization potential. 4) Ionization of the nonmetal X(g) + e- → X-(g) ΔH4 This is electron affinity. 5) Formation of the ionic solids M+(g) + X-(g) → M+X-(s) ΔHL Equation the enthalpies gives ΔHf = ΔH1 + ΔH2 + ΔH3 + ΔH4 + ΔHL from which ΔHL can be found.

a very special type of Hess' Law cycle

electron affinity ideal gas Nernst equation simple cubic structure