Raoult’s Law & Real Solutions

Raoult’s Law:

• For an ideal solution, the partial vapor pressure of each component is proportional to its mole fraction in

• $P_i = X_i \cdot P_i^0$

• 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:

  • $P_{\text{total}} = \sum X_i \cdot P_i^0$

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.

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