The discussion focuses on the physical mechanism behind the fuming of oleum, particularly the role of dissolved SO3 and its reaction with air humidity. Participants explore why mist forms instead of the created H2SO4 dissolving in the solution, examining the conditions and reactions involved.
Participants express differing views on the mechanisms involved in oleum fuming, with no consensus reached on the primary cause of mist formation or the specifics of the reactions taking place.
The discussion includes assumptions about the physical properties of SO3 and H2SO4, as well as the conditions under which the reactions occur. There are unresolved questions regarding the exact nature of the vapors and their interactions.
Readers interested in physical chemistry, chemical engineering, or the behavior of acid solutions may find this discussion relevant.
sludger13 said:Why does the mist occur instead of dissolving created H2SO4 in the solution?
You've pretty much answered your own question here.sludger13 said:SO3 reacts very exothermically with some air humidity
No, that is too simplified.Bystander said:You've pretty much answered your own question here.
Cp(H2SO4, liq) ~ 60 J/molK, and the enthalpy of the reaction between SO3 and water vapor at the surface is around 160 kJ/mol. Fume? You bet you --- that's the old "acid to water, never water to acid" rule from HS chemistry.sludger13 said:Or sulfuric acid with (~300°C, p(atm)) boiling point?
That makes me more sense, thank you.Borek said:My bet is that the concentration (partial pressure) of SO3 above oleum is high enough to start condensation in the presence of water vapor. That will happen above the surface, in the gas phase.
When water putted into acid or conversely acid putted into water, the liquid may spit around due to gas expansion, as I see. Also that is different physical process than oleum fuming.Bystander said:Fume? You bet you --- that's the old "acid to water, never water to acid" rule from HS chemistry.