Endothermic process - wikipedia Endothermic process This article is about the physical effect. For self - maintained thermal homeostasis, see Endotherm. The term endothermic process describes the process or reaction in which the system absorbs energy from its surroundings, usually in the form of heat. The term was coined by Marcellin Berthelot from the Greek roots endo -, derived from the word `` endon '' ( ἔνδον ) meaning `` within '' and the root `` therm '' ( θερμ - ) meaning `` hot '' or `` warm '' intended sense is that of a reaction that depends on absorbing 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, though in reality it only refers to where the energy goes, without necessarily being in the form of heat. All chemical reactions involve both the breaking of existing and the making of new chemical bonds. A reaction to break a bond always requires the input of energy and so such a process is always endothermic. When atoms come together to form new chemical bonds, the electrostatic forces bringing them together leave the bond with a large excess of energy ( usually in the form of vibrations and rotations ). If that energy is not dissipated, the new bond would quickly break apart again. Instead, the new bond can shed its excess energy - by radiation, by transfer to other motions in the molecule, or to other molecules through collisions - and then become a stable new bond. Shedding this excess energy is the exothermicity that leaves the molecular system. Whether a given overall reaction is exothermic or endothermic is determined by the relative contribution of these bond breaking endothermic steps and new bond stabilizing exothermic steps. The concept is frequently applied in physical sciences to, for example, chemical reactions, where thermal energy ( heat ) is converted to chemical bond energy. Endothermic ( and exothermic ) analysis only accounts for the enthalpy change ( ∆ H ) of a reaction. The full energy analysis of a reaction is the Gibbs free energy ( ∆ G ), which includes an entropy ( ∆ S ) and temperature term in addition to the enthalpy. A reaction will be a spontaneous process at a certain temperature if the products have a lower Gibbs free energy ( an exergonic reaction ) even if the enthalpy of the products is higher. Entropy and enthalpy are different terms, so the change in entropic energy can overcome an opposite change in enthalpic energy and make an endothermic reaction favorable. Examples Photosynthesis Melting of ice Evaporating liquid water Sublimation of carbon dioxide ( dry ice ) Cracking of alkanes Thermal decomposition reactions Electrolytic decomposition of sodium chloride into sodium hydroxide and hydrogen chloride Dissolving ammonium chloride in water Nucleosynthesis of elements heavier than nickel in stellar cores High - energy neutrons can 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. Nuclear fusion of elements heavier than iron in supernovae References Jump up ^ Austin, Patrick ( 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. Jump up ^ Qian, Y. - Z. ; Vogel, P. ; Wasserburg, G.J. ( 1998 ). `` Diverse Supernova Sources for the r - Process ''. Astrophysical Journal 494 ( 1 ) : 285 -- 296. arXiv : astro - ph / 9706120. Bibcode : 1998ApJ... 494... 285Q. doi : 10.1086 / 305198. External links Endothermic Definition -- MSDS Hyper - Glossary Chemistry portal Retrieved from `` https://en.wikipedia.org/w/index.php?title=Endothermic_process&oldid=842168552 '' Categories : Thermochemistry Thermodynamic processes Chemical thermodynamics Talk About Wikipedia Afrikaans Български Català Čeština Cymraeg Dansk Deutsch Eesti Ελληνικά Español Esperanto فارسی Français Galego 한국어 हिन्दी Bahasa Indonesia Italiano עברית Kreyòl ayisyen Lietuvių Magyar മലയാളം Nederlands 日本 語 Norsk Norsk nynorsk ਪੰਜਾਬੀ Polski Português Русский Seeltersk Shqip Simple English Slovenščina Soomaaliga Suomi Svenska தமிழ் ไทย Türkçe Українська 中文 35 more Edit links This page was last edited on 20 May 2018, at 18 : 10. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: where does the energy in endothermic reactions come from
Answer: from its surroundings, usually in the form of heat