activation energy(redirected from Activation enthalpy)
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Activation EnergyThe energy in joules needed to convert a mole of a substance from a ground state to a transition state, which allows a chemical reaction to occur.
ac·ti·va·tion e·ner·gy(ak'ti-vā'shŭn en'ĕr-jē)
activation energyThe energy needed to form chemical bonds during a chemical reaction or to break existing ones.
activation energythe energy required to initiate a reaction. Chemical bonds holding molecules together are difficult to break, requiring extra ‘activation’ energy to push the bonded atoms apart. This extra energy makes the bonds less stable so that the molecule releases not only the activation energy but also the energy unlocked when the chemical bonds break, forming an EXERGONIC REACTION.
Activation energy can be applied externally as heat, but this is inappropriate for living organisms. Instead, they rely on biological catalysts (ENZYMES) which decrease the activation energy needed for the reaction to take place. See Fig. 10 . See also ENDERGONIC REACTION.