Equilibrium distribution of polysulfide ions in aqueous solutions at different temperatures by rapid single phase derivatization.

Polysulfides are abundant form of reduced sulfur compounds whose distribution in aquatic systems continues to pose environmental challenge. The Gibbs free-energy of formation, enthalpy of formation, and standard entropy of inorganic polysulfides were derived based on measurements of the temperature-dependent distribution of inorganic polysulfides in supersaturated aqueous polysulfide solutions. The data complements the relevant Gibbs free-energy data that were derived in our recent publication. The thermodynamic data show that the average polysulfide length is increased and polysulfides dissolve better at elevated temperatures, though the extent of this increase is pH dependent. At high pH (pH > 10) increasing the temperature from 25 to 80 degrees C results in a 5.6% increase in the concentration of polysulfide bound sulfur (i.e., dissolved zerovalent sulfur) and increases the average chain length (n) by 0.2 sulfur atoms, whereas at pH 8.2 the n increases by 0.25, and the dissolved polysulfide sulfur increases threefold.