A thermodynamic rationalisation for the oxidising behaviour of concentrated H2SO4

Abstract An attempt is made to extend the principle of equilibrium electrochemical potential–pH diagrams for sulfur compounds in dilute aqueous solutions of sulfuric acid (H 2 SO 4 ) to more concentrated aqueous solutions up to 100 wt.%. Published Hammett acidity data is used to account for the medium effect (undissociated H 2 SO 4 ) on the proton activity. The calculated electrochemical potential‐Hammett acidity diagrams predict a thermodynamic stability domain for all three of the reduction products experimentally observed during cathodic electrolysis, which included sulfur dioxide (SO 2 ), sulfur (S), and hydrogen sulfide (H 2 S). The implications of the relative stability domains on corrosion control measures are discussed.