Exothermic reaction

An exothermic reaction is a chemical reaction where the substances reacting release energy as heat. An example of this is combustion. Exothermic reactions transfer energy to the surroundings. The reaction that does the opposite (it absorbs heat) is an endothermic reaction.

The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to become hotter. The temperature increase can be detected using a thermometer, and the thermal energy by a calorimeter. Some examples of exothermic reactions are:

• burning
• respiration
• neutralisation reactions between acids and alkalis
• the reaction between water and calcium oxide

Exothermic Reaction Media

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  The thermite reaction is famously exothermic. The reduction of iron(III) oxide by aluminium releases sufficient heat to yield molten iron.

• Video of an exothermic reaction. Ethanol vapor is ignited inside a bottle, causing combustion.

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  An energy profile of an exothermic reaction

Related pages

• Heat of combustion