1. Vapor Pressure
William Henry
Francois Marie Raoult

2. Henry’s Law
The concentration of a dissolved gas in a solution is directly proportional to the pressure of the gas above the solution
Applies most accurately for dilute solutions of gases that do not dissociate or react with the solvent
Yes  CO2, N2, O2
No  HCl, HI

3. Raoult’s Law Psolution = Observed Vapor pressure of
The presence of a nonvolatile solute lowers the vapor pressure of the solvent.
Psolution = Observed Vapor pressure of
the solution
solvent = Mole fraction of the solvent
P0solvent = Vapor pressure of the pure solvent

4. Liquid-liquid solutions in which both components are volatile
Modified Raoult's Law:
P0 is the vapor pressure of the pure solvent
PA and PB are the partial pressures

5. Raoult’s Law – Ideal Solution
A solution that obeys Raoult’s Law is called an ideal solution

6. Negative Deviations from Raoult’s Law
Strong solute-solvent interaction results in a vapor pressure lower than predicted
Exothermic mixing = Negative deviation

7. Positive Deviations from Raoult’s Law
Weak solute-solvent interaction results in a vapor pressure higher than predicted
Endothermic mixing = Positive deviation