text: Hess's law is useful in the determination of enthalpies of the following:
  #Heats of formation of unstable intermediates like CO and NO.
  #Heat changes in phase transitions and allotropic transitions.
  #Lattice energies of ionic substances by constructing Born–Haber cycles if the electron affinity to form the anion is known, or
  #Electron affinities using a Born–Haber cycle with a theoretical lattice energy.