Gitterenthalpie

Gitterenthalpie, in English called lattice enthalpy, is a thermodynamic quantity that describes the energy change involved in forming or breaking an ionic lattice. It can be viewed from two complementary perspectives: the energy required to convert one mole of a solid ionic compound into gaseous ions (endothermic, positive value), and the corresponding energy released when gaseous ions come together to form the solid (often referred to as the lattice energy, with the opposite sign of the lattice enthalpy). The two ideas share the same magnitude but opposite signs, depending on the chosen convention.

In thermochemical cycles, especially the Born-Haber cycle, the lattice enthalpy connects the overall formation enthalpy of an ionic compound with the energies of its constituent steps, such as ionization, electron affinity, and bond dissociation energies. The magnitude of the lattice enthalpy increases with higher charges on the ions and with shorter interionic distances; smaller ions with high charges produce especially large lattice energies or enthalpies. The lattice energy is frequently estimated using theoretical models such as the Born-Lande equation or the Kapustinskii approximation, which incorporate factors like the Madelung constant, ionic radii, and charges.

Experimental determination is challenging, so lattice enthalpies are often inferred from related thermochemical data rather than measured directly. A typical example is sodium chloride, for which the lattice enthalpy is about 787 kJ/mol (the lattice energy of formation from gaseous ions is approximately −787 kJ/mol). Lattice enthalpy values help explain trends in properties such as melting points, solubility in water, and hydration behavior, serving as a key parameter in predicting the stability of ionic compounds.