ABSTRACT
The total chemical energy contained in a chemical system is called the internal energy of the system, and is given the symbol U. This internal energy consists of the sum of all the various kinetic and potential energy contributions made to the system by its constituent atoms and molecules. This includes contributions from electrons, chemical bonds, subatomic particles contained in the atomic nuclei, etc., as well as from any other energy contributions not yet discovered. Because of our lack of knowledge about all the types of energies that may be present, it is impossible to measure absolute values of U.
