exchange with hydrogen in the solvent. The product species H3O+ (or D3O+) is a stronger acid than the solute acid, so that it dissociates more easily, and its H–O (or D–O) bond is weaker than the H–A (or D–A) bond of the solute acid. The decrease in zero-point energy due to isotopic substitution is therefore less important in D3O+ than in DA so that KD < KH, and the deuterated acid in D2O is weaker than the non-deuterated acid in H2O. In many cases the difference of logarithmic constants pKD – pKH is about 0.6, so that the pD corresponding to 50% dissociation of the deuterated acid is about 0.6 units higher than the pH for 50% dissociation of the non-deuterated acid. For similar reasons the self-ionization of heavy water is less than that of ordinary water at the same temperature. See also Determination of equilibrium constants Stability constants of complexes Equilibrium fractionation References Data sources IUPAC SC-Database A comprehensive database of published data on equilibrium constants of metal complexes and ligands NIST Standard Reference Database 46 : Critically selected stability constants of metal complexes Inorganic and organic acids and bases pKa data in water and DMSO NASA Glenn Thermodynamic Database webpage with links to (self-consistent) temperature-dependent specific heat, enthalpy, and entropy for elements and molecules Equilibrium chemistry Dimensionless numbers of chemistry