The standard enthalpy change of lattice energy, ΔHlatto, is the change in enthalpy for breaking the bonds in one mole of a solid ionic compound and separating its gaseous ions to an infinite distance under standard conditions.
Since a large amount of energy is required to carry out the process, the standard enthalpy change of lattice energy of a compound is always positive (endothermic), e.g.
However, it may be defined as the change in enthalpy when one mole of an ionic solid is formed from its gaseous ions that are initially infinitely apart under standard conditions. If so, it will always be a negative value (exothermic).
The magnitude of the standard enthalpy change of lattice energy increases for ions with higher charge densities, leading to stronger electrostatic forces of attraction between them in the ionic lattice. Hence,
The standard enthalpy change of lattice energy of an ionic compound is determined theoretically using a Born-Haber cycle, as it is very hard to measure it precisely through experiments.