Activation Energy
The 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.Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.
ac·ti·va·tion e·ner·gy
(ak'ti-vā'shŭn en'ĕr-jē)Minimum amount of energy to convert a stable molecule to a reactive molecule.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012
activation energy
The energy needed to form chemical bonds during a chemical reaction or to break existing ones.Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
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Fig. 10 Activation energy . (a) Activation energy required without enzymes. (b) Activation energy required with enzymes. (c) Energy from exergonic reaction.
activation energy
the 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.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005