adsorption

adsorption [ad sôrp′shən, adzôrp′shən]

n.

〚/span> ADSORB, by analogy with ABSORPTION〛

an adsorbing or being adsorbed; adhesion of the molecules of a gas, liquid, or dissolved substance to a surface

adsorptive

adj.

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ad·sorp·tion (ăd-sôrpʹshən, -zôrpʹ-) Activated charcoal in a gas mask attracts toxic gas molecules, allowing the person wearing the mask to breathe fresh air. Clarinda/Academy Artworks n.

The accumulation of gases, liquids, or solutes on the surface of a solid or liquid.

  [From adsorb.]   ad·sorpʹtive (-tĭv) adj.

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Capability of a solid substance (adsorbent) to attract to its surface molecules of a gas or solution (adsorbate) with which it is in contact.

Physical adsorption depends on van der Waals forces of attraction between molecules and resembles condensation of liquids. In chemical adsorption (often called chemisorption; see catalysis), the gas is held to the surface by chemical forces specific to the chemicals involved, and formation of the bond may require an activation energy.

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▪ surface phenomenon

      capability of all solid substances to attract to their surfaces molecules of gases or solutions with which they are in contact. Solids that are used to adsorb gases or dissolved substances are called adsorbents; the adsorbed molecules are usually referred to collectively as the adsorbate. An example of an excellent adsorbent is the charcoal used in gas masks to remove poisons or impurities from a stream of air.

      Adsorption refers to the collecting of molecules by the external surface or internal surface (walls of capillaries or crevices) of solids or by the surface of liquids. Absorption, with which it is often confused, refers to processes in which a substance penetrates into the actual interior of crystals, of blocks of amorphous solids, or of liquids. Sometimes the word sorption (absorption) is used to indicate the process of the taking up of a gas or liquid by a solid without specifying whether the process is adsorption or absorption.

      Adsorption can be either physical or chemical in nature. Physical adsorption resembles the condensation of gases to liquids and depends on the physical, or van der Waals (van der Waals forces), force of attraction between the solid adsorbent and the adsorbate molecules. There is no chemical specificity in physical adsorption, any gas tending to be adsorbed on any solid if the temperature is sufficiently low or the pressure of the gas sufficiently high. In chemical adsorption, gases are held to a solid surface by chemical forces that are specific for each surface and each gas. Chemical adsorption occurs usually at higher temperatures than those at which physical adsorption occurs; furthermore, chemical adsorption is ordinarily a slower process than physical adsorption and, like most chemical reactions, frequently involves an energy of activation.

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