Raoult’s Law:
For an ideal solution, the partial vapor pressure of each component is proportional to its mole fraction in the solution:
Pi is the partial vapor pressure of component iii.
Xi is the mole fraction of component iii in the liquid phase.
Pi0 is the vapor pressure of the pure component iii.
The total vapor pressure of the solution is the sum of the partial pressures:
Real Solutions
Deviations from Raoult’s Law:
Positive Deviation:
Occurs when the intermolecular forces between unlike molecules are weaker than those between like molecules, resulting in a higher total vapor pressure than predicted by Raoult’s Law.
Example: Ethanol and hexane.
Negative Deviation:
Occurs when the intermolecular forces between unlike molecules are stronger than those between like molecules, resulting in a lower total vapor pressure than predicted by Raoult’s Law.
Example: Acetone and chloroform.