Exothermic
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In thermodynamics, the word exothermic describes a process or reaction that releases energy in the form of heat. Its etymology stems from the Greek prefix ex-, meaning “outside” and the Greek word thermein, meaning “to heat”. The opposite of an exothermic process is an endothermic process, one that absorbs energy in the form of heat. The term “exothermic” was coined by Marcellin Berthelot.
The concept is frequently applied in physical sciences to e.g. chemical reactions, where chemical bond energy is converted to thermal energy (heat).
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[edit] 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 (i.e. a system that does not give off heat to the surroundings), an exothermic process results in an increase in temperature.[1]
[edit] 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
[edit] 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 is placed as a product on the product's side (heat is a product of the reaction).