Endergonic
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Endergonic means absorbing energy in the form of work. Its etymology stems from the suffix -ergonic, as derived from the Greek root ergon, meaning work, combined with the prefix end-, as derived from the Greek root en, meaning put into. Endergonic reactions are not spontaneous. By thermodynamic standards, work, a form of energy, is defined as moving from the surroundings (the external region) to the system (the internal region). Thus, an endergonic process, as contrasted with an exergonic process, is one wherein the system absorbs energy from the surroundings. As a result, during an endergonic process, energy is put into the system. If the transformation occurs at constant pressure and temperature, ∆G > 0. An endergonic reaction is a chemical reaction that absorbs energy in the form of work. A good example of an endergonic reaction is photosynthesis.
An endergonic reaction is, in essence, the opposite of an exergonic reaction. Since endergonic reactions require energy, they form molecular bonds, which decreases entropy. These bonds are energy carriers, so the formation of these bonds requires some energy input.
'Cold packs,' which become cold after mixing two liquids, exploit this property. In fact, a common reaction that is clearly endergonic is the mixing of ammonium chloride and water. There is a net drop in temperature of the reaction as a result of the solvation of ammonium ions.
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