 Revised Release on the Ionization Constant of H2O (2024) by IAPWS

IAPWS R11-24, adopted June 2024. The International Association for the Properties of Water and Steam publishes the formulation.

Nomenclature and section 3 declare a dimensionless ionization constant, molal ionic standard states and a mole-fraction water standard state. Section 6, Table 3 gives temperature- and pressure-dependent values; the near-ambient 25-degree value is approximately ten to the minus fourteen.