The Lattice Energy
The lattice energy is the enthalpy change required to separate one mole of an ionic compound into its ions:
NaCl(s) ® Na+(g) + Cl-(g) DH = 788 kJ
Lattice energy increases with increasing ionic charges and decreasing ionic sizes.
KCl(s) ® K+(g) + Cl-(g) DH = 701 kJ
MgCl2(s) ® Mg+2(g) + 2 Cl?(g) DH = 3795 kJ