[allthingschm]

Is there a difference in acidity or basicity in aqueous and gas phase? i.e. HNO3 is more acidic than H2SO4 in aqueous solutions but what about in gas phase? My reason for wondering if there's a difference is because in aq phase, all bonds are free to rotate but in gas phase, bonds are fixed hence angles are fixed and i wonder if the "immobility" of the bonds which hence affects the steric factors will cause a change in acidity in gas phase?

[Arkcon]

Most definitely.  However, before this discussion goes off the rails, you're going to have to carefully define your definition of "acidity".  For example, in aqueous solution, an acid that can dissociate does so differently than if its in a vapor phase.  I would also ask if you mean in the rarefied, charged, environment of a mass spectrometer's collision cell, because that is likewise a different sort of reaction.

[Irlanur]

If you look at it in a very global way, an acid in the gas phase is not the same system as an acid in solution.

[Enthalpy]

[...] in gas phase, bonds are fixed [...]

Why?