Chemical energy is the potential of a chemical substance to undergo a transformation through a chemical reaction or, to transform into other chemical substances. Forming or breaking chemical bonds involves energy, which can either be absorbed or evolve from a chemical system. Energy is stored in the bonds between atomic nuclei and electrons in the atoms of a molecule. The electrons can be at certain distances from the atomic nucleus, according to the model of the so-called electron layer. The situation in which an electron is in its lowest possible energy state is called the fundamental state.
Related to chemical energy there is another useful term is the heat of combustion, which is the energy released in the combustion reaction and often applied to the study of fuels.
In thermodynamic chemistry the term used for potential energy is the chemical potential, and the Gibbs-Duhem equation is often used for chemical transformation.
The energy that can be released (or absorbed) by a reaction between a set of chemical substances is equal to the difference between the amount of energy of the products and of the reagents. This change in energy is called internal energy of a chemical reaction.
The change of internal energy of a process is equal to the change of heat if measured under conditions of constant volume, as in a calorimeter. However, under conditions of constant pressure, the measured heat does not always equal the internal energy change. The change of heat at constant pressure is called enthalpy change.
Potential chemical energy
Potential chemical energy is a form of potential energy related to the structural arrangement of atoms or molecules. This arrangement may be the result of chemical bonds between the molecules. The chemical energy of a substance can be transformed into other forms of energy by chemical reaction.
Examples of chemical reactions are found in several examples:
- Photovoltaic solar panels transform solar radiation into electrical energy thanks to the photovoltaic effect. Precisely, the photovoltaic effect causes the displacement of an electron from the silicon.
- Thermal power plants get heat by burning fossil fuels, which they will later use to generate electricity.
- Plants obtain energy by transforming solar energy into chemical energy in photosynthesis.
- Electric energy can be converted into chemical energy through electrochemical reactions.
The similar term of chemical potential is used to indicate the potential of a substance to undergo a configuration change, in the form of chemical reaction, space transport, particle exchange with a reservoir.
The term chemical potential is used to indicate the potential of a substance to undergo a configuration change, whether in the form of a chemical reaction, space transport, the exchange of particles with a reservoir, etc.
The chemical potential is not a form of potential energy in itself, but is more closely related to free energy. The confusion in terminology arises from the fact that in other areas of physics not dominated by entropy, all potential energy is available to perform useful work and drives the system to undergo configuration changes spontaneously, and therefore there is no distinction between "free" and potential energy "not free" (hence the word "potential").
However, the total amount of energy present, and conserved by the first law of thermodynamics, of which this chemical potential energy is a part, is separated from the amount of that energy ( thermodynamic free energy from which the chemical potential is derived ), which seems to propel the system forward spontaneously as its entropy increases according to the second law of thermodynamics.