Chemical Energy

Chemical Energy

Chemical energy is the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. Making and breaking chemical bonds involves energy or heat, which may be either absorbed or evolved from a chemical system.

The energy that can be released because of a reaction between a set of chemical substances is equal to the difference between the energy content of the products and the reactant. This change in energy is called the change in internal energy of a chemical reaction.

The change in internal energy is a process which is equal to the heat change if it is measured under conditions of constant volume, as in a closed rigid container such as a bomb calorimeter. However, under conditions of constant pressure, as in reactions in vessels open to the atmosphere, the measured heat change is not always equal to the internal energy change, because of pressure-volume work also releases or absorbs energy. 

Another useful term is the heat of combustion, which is the energy released due to a combustion reaction and often applied in the study of fuels. 



In chemical thermodynamics, the term used for the chemical potential energy is chemical potential, and for chemical transformation an equation most often used is the Gibbs-Duhem equation. 

Chemical Reactions 

In most cases of interest in chemical thermodynamics there are internal degrees of freedom  and processes, such as chemical reactions and phase transitions, which always create entropy unless they are at equilibrium, or are maintained at a "running equilibrium" through "qua-static" changes by being coupled to constraining devices, such as pistons and electrodes, to deliver and receive external work. Even for homogeneous "bulk" materials, the free energy functions depend on the composition, as do all the extensive thermodynamic potentials, including the internal energy.