Gas Solubility o Two contributions from the energy associated with Gas solubility ?

Gas Solubility
• Two contributions from the energy associated with Gas solubility
❑ Energy is absorbed to open “Pockets” in the solvent that can hold gas molecules.

❑ Energy is released when gas molecules enter the pockets.

• The stronger the attraction between gas and solvent, the more heat
released.
• Heat of solution for gases in organic solvents are often endothermic
❑ Since the energy required to open the pockets is greater than the energy released
by attractions formed between gas and solvent
• Heat of solution for gas in Water is often exothermic
• Since water already have pocket to hold gas molecules, and the energy is released
when water and gas molecules attract each other. Solubility change with
Temperature
• Solubility: The mass of solute that forms a saturated solution with a
given mass of solvent at a specified temperature (gsolute / 100
gsolvent).
• When a solute dissolved in a solvent, heat may be absorbed or
released

If energy absorbed : increasing the temperature will increase the solubility
Energy + Solute undissolved Solute dissolved

If energy is released : increasing the temperature will decrease the solubility
Solute undissolved Solute dissolved + Energy Gases become more soluble at higher Pressures
• The solubilities of solids and liquids are not appreciably affected by pressure,
whereas the solubility of a gas in any solvent is increased as the pressure of the
gas above the solvent increases
• At this point, the concentration of the gas in the solution is larger than before.
Increasing the pressure increases the solubility of gases in a solvent
Gas + solvent solution Le Châtelier’s Principle
17 Henry’s Law
Henry’s law: the concentration of a gas in a liquid at a given
temperature is directly proportional to the partial pressure of
the gas over the solution
Cgas = kH Pgas
• Cgas is the concentration of the gas,
• kH is the Henry’s Law constant for that gas
• Pgas is the partial pressure of the gas above the solution.
𝐶1
𝐶2
Alternatively,
conditions

, where 1 and 2 are the initial and final
𝑃 1
𝑃 2
Solubility in Water vs. P Gases with polar molecules or that react with the solvent are
more soluble in Water
• Polar gases (CO2, SO2, NH3) more soluble in water than non-polar gases (O2,
N2), because they have polar bonds that attract water molecules.
• Soluble gases also react with water to some extent
CO2(aq) + H2O H2CO3(aq) H+(aq) + HCO3
-(aq)
SO2(aq) + H2O H+(aq) + HSO3
-(aq)
SO3(g) + H2O H2SO4(aq)