Dissociation is a reaction in which the molecules of a compound split into smaller components. In many dissociation reactions the smaller components are able to recombine under other conditions; such dissociation is called reversible dissociation. For example, heating causes the reversible dissociation of hydrogen iodide into hydrogen and iodine.
The formation of ions (electrically charged particles) when an acid dissolves in water may also be called dissociation. Known as ionic dissociation, this reaction explains many of the properties of electrolytic solutions, including electrolytic conductivity (see electrolysis).
The extent to which dissociation proceeds is indicated by the dissociation constant (which is equal to the equilibrium constant of the reaction).