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 ?
the energy barrier difference between a 2-D liquid-like and a crystal-like structure) is about 2.
This can be interpreted to be due to strong adsorption (improved joint adsorption) process on amorphous surface leading to increase in the energy barrier for the corrosion reaction compared with that in absence of [Cl.
In the basic rate equation, the reaction rate constant is dependent on two factors: the frequency of collisions that have the correct geometry for a reaction to occur and the fraction of those molecules that have the minimum energy required to overcome the activation energy barrier.
The relatively low energy barrier and short cure induction time are indicative of a better co-curing of the NR/BEPDM blends.
Shifting neighboring planes requires the atoms to overcome an energy barrier.
All three lower the the energy barrier of the reaction.
Both, however, require a small additional voltage (an "external bias") to overcome the thermodynamic energy barrier for proton reduction into hydrogen gas.
1 M), a repulsive energy barrier exists in the interaction energy profile in the region 0.
However, he says, the researchers' calculations consider only 32 water molecules around each ion and don't include an energy barrier that water molecules must overcome as they change their structure and permit passage of the ions.
If the valence and conduction bands are separated by an energy barrier that's large enough to prevent any of the electrons in the valence band from being excited to the conduction band at room temperature, then the material is an electrical insulator.
Wet dross can easily bleed inclusions into molten aluminum because the surface energy barrier is already overcome.