activation energy


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activation energy

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.
Activation energyclick for a larger image
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.

activation

the process of activating.

activation analysis
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.
activation energy
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.
activation factor
activation unit
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.
References in periodicals archive ?
From the activation energy plot, it is clear that the activation energy for 25% and 40% conversion (degradation) reached the optimum level in compounds IV and V.
The calculated value of activation energy is an evidence of dipolar polarization.
The kinetic parameters (apparent activation energy E and frequency factor A) were determined using the Friedman procedure, maximum pyrolysis rate method and parallel reactions model, respectively.
The activation energy and the pre-exponential factor are found to be 33 172 kJ/kmol at 8.
At temperature T strain mechanism with potential barrier not exceeding 50kT may be activated due to heat fluctuations [8, 14], whereby the strain will be controlled by the mechanism, which has maximum activation energy among all possible mechanisms for this material [15].
This model describes the effect that temperature has on a chemical process with a certain activation energy.
Other methods include SEM, SAXS, FTIR, DSC DMA, GC/MS, optical microscopy, fatigue behavior, multiaxial stress, residual stress analysis, punch resistance, creep-rupture, impact, oxidative induction time, craze testing, defect analysis, fracture toughness, and activation energy of degradation.
It begins with a chapter on the introduction to reaction kinetics in general, reaction mechanisms, reaction rates, and activation energy.
On the other hand, the activation energy of the reaction is close to that measured in aqueous solutions but higher than that in alcohols.
The surface activation energy required from the flaming process for preparation of surfaces prior to the application of the SICOR fluid for a part that is to be painted is higher than that for a surface being prepared for adhesion.