Chemical Equilibria in Compositional Data

Abstract

Chemical equilibria are typically formulated in terms of concentrations and depend on temperature and thermodynamical constants. In simple systems (e.g. aqueous diluted solutions), these equilibria are governed by the chemical master equation or equilibrium constant. In natural systems the chemical composition is often observed incompletely and relative, i.e. according to the compositional principles. This contribution shows how the chemical master equation is related to the geometry of the Aitchison simplex. If the reaction in equilibrium preserve the amount of matter, the equilibrium defines a hyperplane in the Aitchison simplex. When the reaction does not preserve the amount of matter, the equilibrium can be used to infer the total matter per unit volume.