Why is solubility of HBr Less Than HCl ?

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SUMMARY

The solubility of HBr is measured at a maximum concentration of 8.9 moles/L, which is lower than HCl's maximum concentration of 12 moles/L. Key factors influencing this discrepancy include the enthalpy of formation (-53 kJ/mole for HBr vs. -96 kJ/mole for HCl), enthalpy of hydration (-64 kJ/mole for HBr vs. -60 kJ/mole for HCl), and vapor pressures (16 mmHg for HBr vs. 28 mmHg for HCl). Despite HBr having a more negative free energy, the size of the ion and other thermodynamic properties must be considered to understand the solubility differences.

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morrobay
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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
Ka .........9>>>>>>>>>>>>>>>>>>>>>>7
ΔG=-RTlnKeq(Ka)......<<<<<<<<<<<<<<<<<<<<<<<<
Acid strength........>>>>>>>>>>>>>>>>>>>>>>>>
pH.........-.95>>>>>>>>>>>>>>>>>>>>>-1.08
dissolved mass......712g>>>>>>>>>>>>>>>>>>>>>>432g
 
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morrobay said:
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
Ka .........9>>>>>>>>>>>>>>>>>>>>>>7
ΔG=-RTlnKeq(Ka)......<<<<<<<<<<<<<<<<<<<<<<<<
Acid strength........>>>>>>>>>>>>>>>>>>>>>>>>
pH.........-.95>>>>>>>>>>>>>>>>>>>>>-1.08
dissolved mass......712g>>>>>>>>>>>>>>>>>>>>>>432g

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
 
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.