AskDefine | Define exothermic

Dictionary Definition

exothermic adj : (of a chemical reaction or compound) occurring or formed with evolution of heat [syn: exothermal, heat-releasing] [ant: endothermic]

User Contributed Dictionary



From exo- "outside" + thermic "of heat"


  1. chemistry of a reaction That releases energy in the form of heat.
  2. chemistry of a compound That releases heat during its formation, and absorbs it during its decomposition
  3. Of an animal whose body temperature is regulated by external factors; cold-blooded


Extensive Definition

In thermodynamics, the word exothermic "outside heating" describes a process or reaction that releases energy usually in the form of heat, but it can also release energy in form of light (e.g. explosions), sound, or electricity (e.g. a battery). Its etymology stems from the Greek prefix ex-, meaning “outside” and the Greek word thermein, meaning “to heat”. The term “exothermic” was first coined by Marcellin Berthelot. The opposite of an exothermic process is an endothermic process, one that absorbs energy in the form of heat.
The concept is frequently applied in physical sciences to chemical reactions, where chemical bond energy is converted to thermal energy (heat).


Exothermic refers to a transformation in which a system releases energy (heat) to the surroundings:
Q < 0
When the transformation occurs at constant pressure:
∆H < 0
and constant volume:
∆U < 0
In an adiabatic system (e.g. a system that does not give off heat to the surroundings), an exothermic process results in an increase in temperature.
In chemical reactions, the heat that is released is in the form of electromagnetic energy. The loss of kinetic energy via reacting electrons causes light to be released. This light is equivalent in energy to the stabilization energy of the energy for the chemical reaction, i.e. the bond energy. This light that is released can be absorbed by other molecules in solution to give rise to molecular vibrations or rotations, which gives rise to the classical understanding of heat. In contrast, when endothermic reactions occur, energy is absorbed to place an electron in a higher energy state, such that the electron can associate with another atom to form another chemical complex. The loss of energy within solution is absorbed by the endothermic reaction and therefore is a loss of heat. This is the physical understanding of exothermic and endothermic reactions within solution.


Some examples of exothermic processes are:

Implications for chemical reactions

Chemical exothermic reactions are generally more spontaneous than their counterparts, endothermic reactions. In a thermochemical reaction that is exothermic, the heat may be listed among the products of the reaction.

External links


exothermic in Arabic: تفاعل طارد للحرارة
exothermic in Catalan: Reacció exotèrmica
exothermic in Danish: Exoterm
exothermic in German: exotherm
exothermic in Spanish: Reacción exotérmica
exothermic in Estonian: Eksotermiline reaktsioon
exothermic in French: Réaction exothermique
exothermic in Hebrew: תגובה אקסותרמית
exothermic in Hungarian: Exoterm reakció
exothermic in Italian: Processo esotermico
exothermic in Lithuanian: Egzoterminis procesas
exothermic in Macedonian: Егзотермна реакција
exothermic in Dutch: exotherm
exothermic in Norwegian Nynorsk: Eksoterm reaksjon
exothermic in Slovak: Exotermická reakcia
exothermic in Finnish: Eksoterminen reaktio
exothermic in Swedish: Exoterm
exothermic in Turkish: Ekzotermik
exothermic in Chinese: 放热反应
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