Complex sentence: It is usually defined as the enthalpy of formation of the ionic compound from gaseous ions and as such is invariably exothermic, lattice energy may also be defined as the energy required to completely separate one mole of a solid ionic compound into gaseous ionic constituents.
Split into simpler sentences: It is usually defined as the enthalpy of formation of the ionic compound from gaseous ions and as such is invariably exothermic. Lattice energy may also be defined as the energy required to completely separate one mole of a solid ionic compound into gaseous ionic constituents.