Facts : 1 According to the theories of Svante Arrhenius, this must be due to the presence of ions
Facts : 2 The ions are produced by the self-ionization reaction H2O + H2O H3O + OH This equilibrium applies to pure water and any aqueous solution
Facts : 3 Expressed with activities a, instead of concentrations, the thermodynamic equilibrium constant for the water ionization reaction is: which is numerically equal to the more traditional thermodynamic equilibrium constant written as: under the assumption that the sum of the chemical potentials of H and H3O is formally equal to twice the chemical potential of H2O at the same temperature and pressure
Facts : 4 Because the activity of water, as the solvent in a very dilute solution, is assumed to be unity, the ionic product of water can be also expressed on an activity basis as: In dilute aqueous solutions, the activities of the solute particles are essentially equal to their concentrations
Facts : 5 Thus, the ionization constant, dissociation constant, self-ionization constant, or ionic product of water, symbolized by Kw, may be given by: where [H3O] is the concentration of hydrogen or hydronium ion, and [OH] is the concentration of hydroxide ion
Facts : 6 This is analogous to the notations pH and pKa for an acid dissociation constant, where the symbol p denotes a cologarithm