chemical thermodynamics Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurem ...

, an exergonic reaction is a

chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking ...

where the change in the free energy is negative (there is a net release of free energy). This indicates a spontaneous reaction if the system is

closed Closed may refer to: Mathematics * Closure (mathematics), a set, along with operations, for which applying those operations on members always results in a member of the set * Closed set, a set which contains all its limit points * Closed interval, ...

and initial and final temperatures are the same. For processes that take place in a closed system at constant pressure and temperature, the

Gibbs free energy In thermodynamics, the Gibbs free energy (or Gibbs energy; symbol G) is a thermodynamic potential that can be used to calculate the maximum amount of work that may be performed by a thermodynamically closed system at constant temperature an ...

is used, whereas the Helmholtz energy is relevant for processes that take place at constant volume and temperature. Any reaction occurring at constant temperature without input of electrical or photon energy is exergonic, according to the

second law of thermodynamics The second law of thermodynamics is a physical law based on universal experience concerning heat and energy interconversions. One simple statement of the law is that heat always moves from hotter objects to colder objects (or "downhill"), unle ...

. An example is

cellular respiration Cellular respiration is the process by which biological fuels are oxidised in the presence of an inorganic electron acceptor such as oxygen to produce large amounts of energy, to drive the bulk production of ATP. Cellular respiration may be des ...

. Symbolically, the release of free energy, , in an exergonic reaction (at constant pressure and temperature) is denoted as :

\Delta G=G_-G_<0.\,

Although exergonic reactions are said to occur ''spontaneously'', this does not imply that the reaction will take place at an observable rate. For instance, the disproportionation of hydrogen peroxide releases free energy but is very slow in the absence of a suitable catalyst. It has been suggested that ''eager'' would be a more intuitive term in this context. More generally, the terms

exergonic An exergonic process is one which there is a positive flow of energy from the system to the surroundings. This is in contrast with an endergonic process. Constant pressure, constant temperature reactions are exergonic if and only if the Gibbs ...

and

endergonic In chemical thermodynamics, an endergonic reaction (; also called a heat absorbing nonspontaneous reaction or an unfavorable reaction) is a chemical reaction in which the standard change in free energy is positive, and an additional driving fo ...

relate to the free energy change in any process, not just chemical reactions. By contrast, the terms

exothermic In thermodynamics, an exothermic process () is a thermodynamic process or reaction that releases energy from the system to its surroundings, usually in the form of heat, but also in a form of light (e.g. a spark, flame, or flash), electricity ...

and

endothermic In thermochemistry, an endothermic process () is any thermodynamic process with an increase in the enthalpy (or internal energy ) of the system.Oxtoby, D. W; Gillis, H.P., Butler, L. J. (2015).''Principle of Modern Chemistry'', Brooks Cole. ...

relate to an

enthalpy Enthalpy , a property of a thermodynamic system, is the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant ...

change in a closed system during a process, usually associated with the exchange of

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

References

{{Portal bar, Chemistry Thermochemistry Thermodynamic processes

See also

References