Absorption, in chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules, or ions enter some bulk phase - gas, liquid or solid material. This is a different process from adsorption, since the molecules are taken up by the volume, not by surface. A more general term is sorption which covers adsorption, absorption, and ion exchange. For other uses, see Chemistry (disambiguation). ... For other uses, see Phenomena (disambiguation). ... In science, a process is any method (or event) that results in a transformation in a physical or biological object, a substance or an organism. ... Properties For other meanings of Atom, see Atom (disambiguation). ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... This article is about the electrically charged particle. ... For other uses, see Gas (disambiguation). ... For other uses, see Liquid (disambiguation). ... For other uses, see Solid (disambiguation). ... Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film (the adsorbate). ... Sorption refers to the total action of both absorption and adsorption. ... Adsorption is a process that occurs when a gas or liquid solute accumulates on the surface of a solid or, more rarely, a liquid (adsorbent), forming a molecular or atomic film (the adsorbate). ... Ion exchange is defined as an exchange of ions between two electrolytes. ...

If absorption is a physical process not accompanied by any other physical or chemical process, it usually follows the Nernst partition law:

"the ratio of concentrations of some solute species in two bulk phases in contact is constant for a given solute and bulk phases";

The value of constant K_N depends on temperature and is called partition coefficient. This equation is valid if concentrations are not too large and if the species "x" does not change its form in any of the two phases "1" or "2". If such molecule undergoes association or dissociation then this equation still describes the equilibrium between "x" in both phases, but only for the same form - concentrations of all remaining forms must be calculated by taking into account all the other equlilibria. Dissociation in chemistry and biochemistry is a general process in which complexes, molecules, or salts separate or split into smaller molecules, ions, or radicals, usually in a reversible manner. ...

In the case of gas absorption, one may calculate its concentration by using e.g. the Ideal gas law, c = p/RT. Alternatively, one may use partial pressures instead of concentrations. Isotherms of an ideal gas The ideal gas law is the equation of state of a hypothetical ideal gas, first stated by Benoît Paul Émile Clapeyron in 1834. ... In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. ...

In many technologically important processes, the chemical absorption is used in place of the physical process, e.g. absorption of carbon dioxide by sodium hydroxide - such processes do not follow the Nernst partition law.

For some examples of this effect see liquid-liquid extraction, it is possible to extract from one liquid phase to another a solute without a chemical reaction. Examples of such solutes are noble gases and osmium tetroxide. Liquid-liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds based on their solution preferences for two different immiscible liquids, usually water and an organic solvent. ... For other uses, see Liquid (disambiguation). ... A substance is soluble in a fluid if it dissolves in the fluid. ... The noble gases are a chemical series. ... The chemical compound osmium tetroxide (OsO4), also known as osmium tetraoxide, osmium(VIII) oxide, or osmic acid, is an oxide of the element osmium. ...