The chemical reaction equilibrium constant and standard molar enthalpy change for the reaction {2HSO3-(aq)⇌S2O52-(aq)+H2O(l)}: a spectroscopic and calorimetric investigation

The chemical reaction equilibrium constant for the formation of pyrosulfite from bisulfite in aqueous solutions {2HSO3-(aq)⇌S2O52-(aq)+H2O(l)} was determined for temperatures from (313 to 353) K from ATR-IR-spectroscopic and calorimetric investigations of the system (Na2S2O5 + H2O), resulting in ln K = −10.226 + 2123.6/(T/K), ΔrGm∘=(7.69±0.33)kJ·mol-1,ΔrHm∘=(-17.7±0.5)kJ·mol-1 (on the molality scale). Furthermore, some ATR-IR-spectroscopic results on liquid mixtures of (NH3 + SO2 + H2O) at T = 313 K are presented, revealing considerable amounts of pyrosulfite.