In thermodynamics, the word endothermic describes a process or reaction in which the system absorbs energy from its surroundings in the form of heat. It is a modern coinage from Greek roots. The prefix endo- derives from the Greek word "endon" (ἔνδον) meaning "within," and the latter part of the word comes from the Greek word root "therm" (θερμ-) meaning "hot." The intended sense is that of a reaction that depends on taking in heat if it is to proceed. The opposite of an endothermic process is an exothermic process, one that releases, "gives out" energy in the form of heat. Thus in each term (endothermic & exothermic) the prefix refers to where heat goes as the reaction occurs. The term endothermic was coined by Marcellin Berthelot (25 October 1827 – 18 March 1907).
Implications for chemical reactions
Chemical endothermic reactions need heat to be performed. In a thermochemical reaction that is endothermic, the heat is placed on the reactants' side (heat is necessary for and absorbed during the reaction). The heat absorbed during the chemical reaction results in a decrease in temperature of its surroundings. This principle is employed in instant cold compresses (ice packs) which are used in first-aid.
Contrast between thermodynamic and biological terminology
Note that because of historical accident, students encounter a possible source of confusion between the terminology of physics and biology. Whereas the thermodynamic terms "exothermic" and "endothermic" respectively refer to processes that give out heat energy and processes that absorb heat energy, in biology the sense is effectively inverted. The metabolic terms "ectothermic" and "endothermic" respectively refer to organisms that rely largely on external heat to achieve a full working temperature, and to organisms that produce heat from within as a major factor in controlling their bodily temperature.
- Melting ice
- Vaporising Rubbing Alcohol
- Thermal decomposition reactions
- Forming a cation from an atom in the gas phase
- Dissolving ammonium chloride in water
- High-energy neutrons can also produce tritium from lithium-7 in an endothermic reaction, consuming 2.466 MeV. This was discovered when the 1954 Castle Bravo nuclear test produced an unexpectedly high yield.
- Hisham Zerriffi (January 1996). "Tritium: The environmental, health, budgetary, and strategic effects of the Department of Energy's decision to produce tritium". Institute for Energy and Environmental Research. Retrieved 2010-09-15.
- Endothermic Definition - MSDS Hyper-Glossary