Partition equilibrium is a special case of

chemical equilibrium In a chemical reaction, chemical equilibrium is the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the ...

. The most common chemical equilibrium systems involve reactants and products in the same phase - either all gases or all solutions. However, it is also possible to get equilibria between substances in different phases, such as two liquids that do not mix (are

immiscible Miscibility () is the property of two substances to mix in all proportions (that is, to fully dissolve in each other at any concentration), forming a homogeneous mixture (a solution). The term is most often applied to liquids but also appli ...

). Partition equilibria are described by

Nernst Walther Hermann Nernst (; 25 June 1864 – 18 November 1941) was a German chemist known for his work in thermodynamics, physical chemistry, electrochemistry, and solid state physics. His formulation of the Nernst heat theorem helped pave the w ...

distribution law Distribution law or the Nernst's distribution law gives a generalisation which governs the distribution of a solute between two non miscible solvents. This law was first given by Nernst who studied the distribution of several solutes between dif ...

Example

For example,

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...

(NH₃) is soluble in both water (aq) and the organic solvent trichloromethane (CHCl₃) - two immiscible solvents. If ammonia is first dissolved in water, and then an equal volume of trichloromethane is added, and the two liquids shaken together, the following equilibrium is established: :K_c = H₃ _(CHCl3) H_{3 (aq)} (where K_c is the

equilibrium constant The equilibrium constant of a chemical reaction is the value of its reaction quotient at chemical equilibrium, a state approached by a dynamic chemical system after sufficient time has elapsed at which its composition has no measurable tendency ...

) The equilibrium concentrations of ammonia in each layer can be established by

titration Titration (also known as titrimetry and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed). A reagent, termed the ''titrant'' ...

with standard acid solution. It can thus be determined that K_c remains constant, with a value of 0.4 in this case.

Partition coefficient

This particular kind of equilibrium constant measures how a substance distributes or partitions itself between two immiscible solvents. It is called the partition coefficient or distribution coefficient.

Polar and non-polar substances

Substances that are ionic or

polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the cli ...

are more soluble in water than in non-polar organic solvents and vice versa.

Partition equilibrium chromatography

Partition equilibrium chromatography is a type of

chromatography In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system ( ...

that is typically used in

gas chromatography Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substanc ...

(GC) and

high performance liquid chromatography High-performance liquid chromatography (HPLC), formerly referred to as high-pressure liquid chromatography, is a technique in analytical chemistry used to separate, identify, and quantify each component in a mixture. It relies on pumps to p ...

(HPLC). The stationary phase in GC is a high boiling liquid bonded to solid surface and the mobile phase is a gas.

Example

Partition coefficient

Polar and non-polar substances

Partition equilibrium chromatography

See also