Absorption (chemistry)

Not to be confused with Adsorption.
Laboratory absorber. 1a): CO2 inlet; 1b): H2O inlet; 2): outlet 3): absorption column; 4): packing.

Absorption is a physical or chemical phenomenon or a process in which atoms, molecules or ions enter the liquid or solid bulk phase of a material. This is a different process from adsorption, since molecules undergoing absorption are taken up by the volume, not by the surface (as in the case for adsorption).

A more common definition is that "Absorption is a chemical or physical phenomenon in which the molecules, atoms and ions of the substance getting absorbed enter into the bulk phase (gas, liquid or solid) of the material in which it is taken up."

A more general term is sorption, which covers absorption, adsorption, and ion exchange. Absorption is a condition in which something takes in another substance.[1]

In many processes important in technology, the chemical absorption is used in place of the physical process, e.g., absorption of carbon dioxide by sodium hydroxide – such acid-base processes do not follow the Nernst partition law (see: solubility).

For some examples of this effect, see liquid-liquid extraction. It is possible to extract a solute from one liquid phase to another without a chemical reaction. Examples of such solutes are noble gases and osmium tetroxide.[1]

The process of absorption means that a substance captures and transforms energy. The absorbent distributes the material it captures throughout whole and adsorbent only distributes it through the surface.

The process of gas or liquid which penetrate into the body of adsorbent is commonly known as absorption.

IUPAC definition

absorption: 1) The process of one material (absorbate) being retained by another (absorbent); this may be the physical solution of a gas, liquid, or solid in a liquid, attachment of molecules of a gas, vapour, liquid, or dissolved substance to a solid surface by physical forces, etc. In spectrophotometry, absorption of light at characteristic wavelengths or bands of wavelengths is used to identify the chemical nature of molecules, atoms or ions and to measure the concentrations of these species. 2) A phenomenon in which radiation transfers to matter which it traverses some of or all its energy. [2]

  1. ^ a b McMurry, John (2003). Fundamentals of Organic Chemistry (Fifth ed.). Agnus McDonald. p. 409. ISBN 0-534-39573-2.
  2. ^ "absorption". Gold Book. IUPAC. 2014. doi:10.1351/goldbook.A00036. Retrieved 1 April 2024.