Lattice energy

The size of the lattice energy is connected to many other physical properties including solubility, hardness, and volatility.

Since it generally cannot be measured directly, the lattice energy is usually deduced from experimental data via the Born–Haber cycle.

[2] Some chemistry textbooks[3] as well as the widely used CRC Handbook of Chemistry and Physics[4] define lattice energy with the opposite sign, i.e. as the energy required to convert the crystal into infinitely separated gaseous ions in vacuum, an endothermic process.

The formation of a crystal lattice from ions in vacuum must lower the internal energy due to the net attractive forces involved, and so

term is positive but is relatively small at low pressures, and so the value of the lattice enthalpy is also negative (and exothermic).

The lattice energy of an ionic compound depends strongly upon the charges of the ions that comprise the solid, which must attract or repel one another via Coulomb's Law.

London dispersion forces also exist between ions and contribute to the lattice energy via polarization effects.

Closely related to this widely used formula is the Kapustinskii equation, which can be used as a simpler way of estimating lattice energies where high precision is not required.

[2] For certain ionic compounds, the calculation of the lattice energy requires the explicit inclusion of polarization effects.

It has been shown that neglect of polarization led to a 15% difference between theory and experiment in the case of FeS2, whereas including it reduced the error to 2%.