Why is solubility of HBr Less Than HCl ?

morrobay

The maximum concentration of dissolved HBr , 8.9 moles/L is less than HCl 12 moles/L
The values from table below from various sources suggest that HBr should be more soluble at STP in 1 liter water ?
...............................................HBr..................... ...............HCl
enthalpy of formation.................-53kJ.mole >>>>>>>>>>>>>>>-96kJ/mole
enthalpy of hydration/dissociation -64kJ/mole<<<<<<<<<<<<<<<-60kJ/mole
vapor pressure........................... 16mmHg<<<<<<<<<<<<<<<<<28mmHg
K_a ...........................................9>>>>>>>>>>>>>>>>>>>>>>7
ΔG=-RTlnK_eq(K_a)........................<<<<<<<<<<<<<<<<<<<<<<<<
Acid strength..............................>>>>>>>>>>>>>>>>>>>>>>>>
pH...........................................-.95>>>>>>>>>>>>>>>>>>>>>-1.08
dissolved mass..........................712g>>>>>>>>>>>>>>>>>>>>>>432g

morrobay

Correction : Vapor pressures at above concentrations HCl , 12 m/l = 15 mm Hg
HBr, 8.9 m/l = 4.5 mm Hg.
Dissolved mass is for general information only
Just based on a more negative free energy alone should indicate a higher maximum concentration for HBr

Borek

I have a gut feeling we can't ignore size of the ion - while the molar values are different, there is only so much of a substance that fits given volume.

Or at least that would be the starting point for my analysis. Doesn't have to yield any explanation.