Calculation of the ionization constant of H₂O to 2,273 K and 500 MPa

Abstract

Abstract Calculations of the ionization constant of H 2 O are presented for densities ranging from those of subcritical water to those of supercritical steam. A recently‐proposed semicontinuum model is used to calculate the standard‐state hydration properties for the ions, H 3 O + , and OH − (Tanger and Pitzer, 1989). Calculated ionization constants are in good agreement with reported measurements at pressures from vapor‐liquid saturation to 500 MPa and temperatures from 273 to 1,073 K. These measurements cover H 2 O densities ranging from ∼ 1,000 to 450 kg · m −3 . At H 2 O densities less than 400 kg · m −3 , our calculated ionization constants should be more reliable than those obtained from the commonly‐used equation of Marshall and Franck (1981).