Hydrates in supersaturated binary sulfuric acid-water vapor

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Abstract
Portions of the free energy surface giving the reversible work W required to form a droplet containing n1 molecules of H2O and n2 molecules of H2SO4 from an initially homogeneous vapor have been calculated for a variety of relative humidities and H2SO4 vapor concentrations. These surfaces are displayed as three dimensional perspective plots. The surfaces predict the existence of stable H2SO4 hydrates in the vapor phase, and the number of hydrates, Nh, with h molecules of H2O per hydrate has been calculated for three different values of the relative humidity. The results of these calculations indicate that virtually all the H2SO4 present, especially for relative humidities greater than 100%, exists in hydrate form. As the relative humidity is increased (i.e., greater than 200%), the distribution of hydrate sized agrees well with that found by Giauque et al. for solid H2O–H2SO4 mixtures. Hydrate formation can exert an appreciable effect on the process of vapor phase nucleation in H2O–H2SO4 mixtures, and must be considered in any theory of nucleation rate.