Exothermic

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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 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).

1 Overview
- 1.1 Exothermic processes
2 Implications for chemical reactions
3 See also
4 External links
5 References

Overview

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.^[1]

Exothermic processes

Some examples of exothermic processes are:^[2]

Condensation of rain from water vapor
Combustion (for instance of a candle)
Mixing water and strong acids
Nuclear fusion

Implications for chemical reactions

Main article: exothermic reaction

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.