Born–Haber Cycles and Lattice Enthalpy (HL)

Ionic compounds are held together by the electrostatic attraction between oppositely charged ions arranged in a giant lattice. The strength of that lattice is quantified by the lattice enthalpy. In this course we define the lattice enthalpy of formation as the enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions, an exothermic process, though many textbooks equivalently use lattice enthalpy of dissociation, the endothermic reverse. We will use the dissociation convention here: the lattice enthalpy is the energy to separate one mole of solid into gaseous ions, for example $\text{NaCl(s)} \rightarrow \text{Na}^+(g) + \text{Cl}^-(g)$, a large positive value. Lattice enthalpies cannot be measured directly, so we determine them indirectly using a Born–Haber cy