Free energy also is a measure of escaping tendency, as the experiment at the bottom left illustrates. Ether and water will not mix; they are mutually insoluble because the polar water molecules can form much stronger interactions by separating from the nonpolar ether molecules into their own phase. If we shake water and ether together in a flask, they divide into two layers upon standing.

Iodine crystals are soluble to a limited extent in both ether and water. If we add a small amount of iodine to the ether phase, some of the deep violet color slowly will appear in the water phase as a brown coloration, and if we add iodine to the water, some of it will diffuse into the ether. The free energy per mole, or chemical potential, of a substance in a mixture depends on its concentration; The higher the concentration, the higher the chemical potential. The spontaneous tendency of molecules to diffuse from regions of high concentration to more dilute regions is another example of the tendency to move from high to low potential. In the ether-water experiment, if iodine is added to the ether, its chemical potential in ether initially is higher than in water; hence iodine molecules migrate from ether to water until their chemical potential or free energy per mole is the same in both phases. When this condition is reached; no further change in free energy is produced by moving a molecule of I₂ from one phase to the other, D G = O for the transfer, and equilibrium exists