In aqueous solution, oxyanions with high charge can undergo condensation reactions, such as in the formation of the dichromate ion, :
The driving force for this reaction is the reduction of electrical charge density on the anion and the elimination of the hydronium () ion. The amount of order in the solution is decreased, releasing a certain amount of entropy which makes the Gibbs free energy more negative and favors the forward reaction. It is an example of an acid–base reaction with the monomeric oxyanion acting as a base and the condensed oxyanion acting as its conjugate acid. The reverse reaction is a hydrolysis reaction, as a water molecule, acting as a base, is split. Further condensation may occur, particularly with anions of higher charge, as occurs with adenosine phosphates.
The conversion of ATP to ADP is a hydrolysis reaction and is an important source of energy in biological systems.
The formation of most silicate minerals can be viewed as the result of a de-condensation reaction in which silica reacts with a basic oxide, an acid–base reaction in the Lux–Flood sense.