Ok most questions (that I have come across) when dealing with the Born Haber Cycle give the Sublimation energy, the Dissociation energy, the Electron Affinity, the Ionization Energy, and the Formation Energy. I know that to get the Formation Energy it is: Hf= Hs+Hi.e.+1/2Hd+He.a.+U (Lattice Energy) My problem is that if everything but the lattice energy is given what is the calculations to get the lattice energy. I know the lattice energy for some examples like NaCl but that's just from memory, I just don't know how to get the lattice energy (assuming that I didn't memorize it) by using a calculation. Can anyone shed some light on this for me? Would be much appreciated.