text: An alternative quantitative approach to inorganic chemistry focuses on energies of reactions.  This approach is highly traditional and empirical, but it is also useful.  Broad concepts that are couched in thermodynamic terms include redox potential, acidity, phase changes.  A classic concept in inorganic thermodynamics is the Born–Haber cycle, which is used for assessing the energies of elementary processes such as electron affinity, some of which cannot be observed directly.