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. Dissociation is the opposite of association and recombination.

Dissociation constant

For reversible dissociations in a chemical_equilibrium

AB <=> A + B

the dissociation constant K_d is the ratio of dissociated to undissociated compound

K_d = ([A] · [B]) / [AB]

Salts

The dissociation of salts by solvation in a solvent like water (molecule) means the separation of the anions and cations. The salt can be recovered by evaporation of the solvent. See also: Solubility equilibrium

Acids

The dissociation of acids in a solution means the split-off of a proton H⁺, see Acid-base reaction theories. This is an equilibrium process, meaning that dissociation and recombination takes place at the same time. The acid dissociation constant K_a is an indicator of the acid strength: stronger acids have a higher K_a value (and a lower pK_a value).

Fragmentation

Adsorption

Receptors

Receptors are proteins that bind small ligands. The dissociation constant K_d is used as indicator of the affinity of the ligand to the receptor. The higher the affinity of the ligand for the receptor the lower the K_d value (and the higher the pK_d value).