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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).

Contents 1 Example 2 Partition coefficient 3 Polar and non-polar substances 4 Partition equilibrium chromatography 5 See also

[edit] Example

For example, ammonia (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 = [NH_{3 (CHCl3)}]/[NH_{3 (aq)}]        (where K_c is the equilibrium constant)

The equilibrium concentrations of ammonia in each layer can be established by titration with standard acid solution. It can thus be determined that K_c remains constant, with a value of 0.4 in this case.

[edit] 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.

[edit] Polar and non-polar substances

Substances that are ionic or polar are more soluble in water than in non-polar organic solvents and vice-versa.

[edit] Partition equilibrium chromatography

Partition equilibrium chromatography is a type of chromatography that is typically used in gas chromatography (GC) and high performance liquid chromatography (HPLC). The stationary phase in GC is a high boiling liquid bonded to solid surface and the mobile phase is a gas.

[edit] See also

• Liquid-liquid extraction

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