Exothermic
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In the physical sciences, the word exothermic, in contrast to the word endothermic, describes a process or reaction that releases energy in the form of heat. The concept is frequently applied to chemical reactions, where chemical bond energy is converted to thermal energy (heat). If the system undergoes a transformation which is both exothermic and adiabatic, i.e. adiabatic meaning that heat is generated internally but no heat is given off to the surroundings, its temperature increases.
Overview
Exothermic means to release energy in the form of heat. Its etymology stems from the Greek suffix –thermic, meaning “to heat”, and the Greek prefix exo-, meaning “outside”. It refers to a transformation in which a system gives heat to the surroundings: Q < 0. When the transformation occurs at constant pressure: ∆H < 0; and constant volume: ∆U < 0. If the system undergoes a transformation which is both exothermic and adiabatic, its temperature increases.A process where heat is released to the surroundings (Qsystem < 0) can also be referred to as "exothermic". If the process occurs at constant pressure, this implies that the enthalpy of the system decreases (∆H < 0); and at constant volume, that the internal energy decreases (∆U < 0).
Chemical exothermic reactions are generally more spontaneous than their counterparts, endothermic reactions (heat is absorbed into the system instead of released). A common type of exothermic reaction is the combustion reaction, in which a substance reacts with oxygen to normally produce carbon dioxide (CO2) gas and water (H2O).
In a thermochemical reaction that is exothermic, the heat is placed as a product on the product's side. Also, the change in enthalpy (heat) is negative for an exothermic reaction. As stated before, exothermic reactions have a generally higher degree of entropy (randomness, basically) than endothermic reactions, and are much more spontaneous.
Key points
- Energy is released.
- Energy is a product of the reaction.
- Reaction vessel becomes warmer.
- Temperature inside reaction vessel increases.
- Energy of the reactants is greater than the energy of the products.
- ∆H = H(products) - H(reactants) = a negative number
See also
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References
External links
- [Exothermic Definition] - MSDS Hyper-Glossary
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