Chemisorption

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chemisorption

[′kem·i‚sȯrp·shən]
(physical chemistry)
A chemical adsorption process in which weak chemical bonds are formed between gas or liquid molecules and a solid surface.

Chemisorption

 

the adsorption of substances from the surrounding medium by a liquid or solid, accompanied by the formation of chemical compounds. In a narrower sense, chemisorption is regarded as the chemical binding of a substance by the surface of a solid, or chemical adsorption.

Considerable heat is released in chemisorption: the heat of chemisorption is usually 84–126 kilojoules per mole (kJ/mole), or 20–30 kcal/mole; in some cases—for example, the chemisorption of oxygen on metals—it may exceed 420 kJ/mole (100 kcal/mole). Like chemical reactions, chemisorption usually requires considerable activation energy. Thus, chemisorption is accelerated when the temperature is increased (activated adsorption). Chemisorption is selective—that is, it depends on the chemical affinity of the adsorbed substance for the solid surface.

Physical methods, such as spectroscopy, electron paramagnetic resonance, nuclear magnetic resonance, electron and ion field-emission microscopy, and slow-electron diffraction, are used to study chemisorption. The process plays an important role in heterogeneous catalysis, gas purification, and vacuum technology.

REFERENCES

See references under ADSORPTION.

M. U. KISLIUK

References in periodicals archive ?
6 confirm that both physisorbed and chemisorbed dodecanoic acid molecules exist in the surface layer.
In an unbaked metal chamber with metal seals and sufficient pumping, it is possible to remove most gas molecules except the chemisorbed water on the chamber walls.
In the case of a chemisorbed anti-wear mechanism when the mixed or boundary lubrication takes place, the temperature will increase and both AW and EP additives can react with the metal surface forming tribochemical reaction layers (iron phosphites, sulfides, sulfates, oxides and carbides--depending on the additive's chemistry) that will prevent a direct contact between the sliding metal surfaces.
Getters are characterized by their chemical affinity for different gases and by the diffusivity of each chemisorbed species into the bulk of the getter material.
All carbon blacks have some level of chemisorbed oxygen complexes (carboxylic, phenolic, quinonic, or lactonic groups), or volatile content, on their surfaces.
At a relatively low temperature (300 [degrees]C) the desorption reaction occurred and the amount of chemisorbed oxygen associated nitrogen (N-X2) decreased significantly.
The silanol then reacts with the hydroxyl group of the fiber, forming stable covalent bonds to the cell wall that are chemisorbed onto the fiber surface [16].
In the DSC cuves, the first decomposition step assignable removal of adsorbed and chemisorbed water is indicated by broad endothermic peak around 109C.
It means that both physisorption and chemisorption may occur on the surface at the same time, a layer of molecules may be physically adsorbed on a top of an underlying chemisorbed layer (Denizli et al.
The higher tafel slopes found at high anodic potential were due to decreasing surface coverage by chemisorbed phenol [25].
It is reported that some HALS compounds are chemisorbed on the pigment surface under losing its free radical scavenging ability.
These complexes are chemisorbed oxygen groups in the form of carboxy, quinone, lactone and phenolic groups (ref.