Lattice energy is the energy required to separate a mole of an ionic solid into gaseous ions.

Lattice energies are also important in predicting the solubility of ionic solids in water.

Lattice energy cannot be measured empirically, but it can be calculated using electrostatics or estimated using the Born Haber cycle and its units are kJ/mol.

**Formula to calculate lattice energy.**

- K is the constant (2.31 x 10 ^ -19)
- Q1 is the numerical ion charge of ion 1.
- Q2 is the numerical ion charge of ion 2.
- R is the distance between ions.

Example:

Na Cl has an ion charge of +1 and -1, calculate the lattice energy if the distance between the two ions is 0.282 nm.

Therefore, the lattice energy is 8.19 x 10^-19kJ/mol.