activation energy (redirected from Activation enthalpy)
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Etymology: L, activus, active
the energy required to convert reactants to transition-state species or an activated complex that will spontaneously proceed to products.
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.
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.
activation energy The energy needed to form chemical bonds during a chemical reaction or to break existing ones.
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.
the process of activating.
a method of analyzing the content of elements in samples of biological material. The sample is bombarded with nuclear particles and the elements in it measured by the radiation emitted by their radioactive daughter products. Called also radioactivation analysis.
the difference in energy between the ground state of the reactants in a reaction and the point of maximum energy or transition state of the reactions. Usually lowered by enzyme catalysts.
the combination of complement (C4, C2 and C3) that binds to the antigen-antibody complex in the initial reaction step in the classical pathway of complement activation. See also complement