Transcript Vapor Pressure - ScienceGeek.net

Vapor
Pressure
William Henry
Francois Marie Raoult
Henry’s Law
The concentration of a dissolved gas in a solution
is directly proportional to the pressure of the gas
above the solution
C  kP
Applies most accurately for dilute solutions of
gases that do not dissociate or react with the
solvent
Yes  CO2, N2, O2
No  HCl, HI
Raoult’s Law
The presence of a nonvolatile solute lowers
the vapor pressure of the solvent.
Psolution   solvent P
0
solvent
Psolution = Observed Vapor pressure of
the solution
solvent = Mole fraction of the solvent
P0solvent = Vapor pressure of the pure solvent
Liquid-liquid solutions in which both
components are volatile
Modified Raoult's Law:
PTOTAL  PA  PB   A P   B P
0
A
P0 is the vapor pressure of the pure solvent
PA and PB are the partial pressures
0
B
Raoult’s Law – Ideal Solution
A solution that obeys Raoult’s Law is called an
ideal solution
Negative Deviations from Raoult’s Law
Strong solute-solvent interaction results in a
vapor pressure lower than predicted
Exothermic mixing = Negative deviation
Positive Deviations from Raoult’s Law
Weak solute-solvent interaction results in a
vapor pressure higher than predicted
Endothermic mixing = Positive deviation