Abstract:A new type of potential pH diagram and distribution curves X(i) pH of aqueous species for the S-H ₂O system have been reported and discussed according to overall equilibrium principle. The stable region of elemental sulfur is dependent on total sulfur concentration C _t(S) of all species in solution and partial pressure p H ₂S / p ⁰ of H ₂S gas. When p H ₂S / p ⁰ =10 ^-6 and C t(S)=1 mol/L, the stable range of sulfur disappears. Dominant region of S 2- 5 ion in the solution corresponds to stable region of solid sulfur in E h pH diagram. This type of E h pH diagrams and distribution curves of aqueous species are of both theoretical and practical importance.

Key words: potential pH diagram thermodynamics S-H ₂O system sulfur