Reversible Chemical Reactions
In the discussion of thermal energy storage in it was pointed out that energy can be stored in both the sensible heat that is related to changes in the temperature of materials and their heat capacities, and the involved in isothermal phase transitions. A common example of such an isothermal phase transition with a significant amount of stored heat is the melting and freezing of water. In such cases, there are no changes in chemical composition. The chemical species below and above the phase transition are the same. Only their physical state is different. Such reactions are said to be congruent.