Chemisorption is a type of adsorption whereby a molecule adheres to a surface through the formation of a chemical bond, as opposed to the Van der Waals forces which cause physisorption. It is characterised by: Not to be confused with absorption. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... An open surface with X-, Y-, and Z-contours shown. ... A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... In chemistry, the term van der Waals force originally referred to all forms of intermolecular forces; however, in modern usage it tends to refer to intermolecular forces that deal with forces due to the polarization of molecules. ... Physisorption is a process whereby a molecule adheres to a surface without the formation of a chemical bond, usually by van der Waals forces or electrostatic attraction. ...
High temperatures.
Type of interaction: strong; covalent bond between adsorbate and surface.
High enthalpy: 50 kJ/mol <ΔH< 800 kJ/mol
Adsorption takes place only in a monolayer.
High activation energy
Increase in electron density in the adsorbent-adsorbate interface.
Reversible only at high temperature.
Uses
The main way in which most chemists utilise the effect of chemisorption is in catalysed reactions. The process of chemisorption is actually pivotal to the role of heterogeneous catalysis where the catalyst is in a solid phase—particularly transition metal catalysts. In many cases the chemical reagents will both bind to the catalytic surface. The chemical bonds then form and draw electrons away from the chemisorption bonds. The molecule then desorbs and is free to leave the surface.
Examples
Self Assembled Monolayers (SAMs) are often formed by chemisorbing thiols (RS-H) onto gold surfaces forming Au-SR bonds.
O2 on carbon at high temperatures
Research on the adsorption of hydrogen onto carbon nanotubes with the aim of producing a fuel cell that can eventually replace our dependence on fossil fuels
Not to be confused with absorption. ... Physisorption is a process whereby a molecule adheres to a surface without the formation of a chemical bond, usually by van der Waals forces or electrostatic attraction. ...
Chemisorption (or chemical adsorption) is adsorption in which the forces involved are valence forces of the same kind as those operating in the formation of chemical compounds.
The problem of distinguishing between chemisorption and physisorption (see below) is basically the same as that of distinguishing between chemical and physical interaction in general.
the energy of chemisorption is of the same order of magnitude as the energy change in a chemical reaction between a solid and a fluid: thus chemisorption, like chemical reactions in general, may be exothermic or endothermic and the magnitudes of the energy changes may range from very small to very large;
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