Chemical bonding forces are responsible for the diversity of substances in the natural environment. But the weak interactions among atoms, molecules and ions have their part to play in the phases in which the substances exist under various conditions. In general, stronger intermolecular forces result in higher heats of fusion, vaporization and sublimation.

The energy used in making these changes (or released when they occur in the opposite direction) is used to overcome the intermolecular forces and becomes stored largely as potential energy within the sample. These phase changes are equilibrium situations (DG = 0) and so looking more closely at them provides an opportunity to examine one more time the relationships involving enthalpy and entropy.