The Born – Haber cycle is used to determine the lattice enthalpy of NaCl as follows:
Formation of NaCl can be considered in 5 steps. The sum of the enthalpy changes of these steps is equal to the enthalpy change for the overall reaction from which the lattice enthalpy of NaCl is calculated.
By the above method, indirectly lattice enthalpy of NaCl is calculated, if the values of ∆Hf°, ∆H1° , ∆H2°- ∆H3° and ∆H4 ° are given.