Vapor-Liquid Equilibrium For Non-Ideal Solutions: Summary



Key points from this module:
  1. When a vapor mixture is cooled or its pressure increases, both components condense. 
  2. Bubble pressure is the pressure where the first bubble of vapor forms as the pressure above a liquid decreases at constant temperature.
  3. Bubble temperature is the temperature where the first bubble of vapor forms as the temperature of a liquid increases at constant pressure. 
  4. Dew pressure is the pressure where the first drop of liquid forms as the pressure of a vapor increases at constant temperature.
  5. Dew temperature is the temperature where the first drop of liquid forms as the temperature of a vapor decreases at constant pressure. 
  6. A positive deviation from Raoult's law means the pressure above the liquid mixture is greater than that calculated from Raoult's law because the interactions between A and B molecules are weaker than the average A-A and B-B interactions.
  7. A negative deviation from Raoult's law means the pressure above the liquid mixture is less than that calculated from Raoult's law because the interactions between A and B molecules are stronger than the average of A-A and B-B interactions.
  8. An azeotrope corresponds to a maximum or minimum in the pressure versus mole fraction plot. At an azeotrope, the liquid and vapor compositions are identical, which makes separations by distilliation difficult.
  9. A system with maximum-pressure azeotrope will have a minimum-temperature azeotrope.
  10. A system with minimum-pressure azeotrope will have a maximum-temperature azeotrope. 

From studying this module, you should now be able to:
  1. Construct a P-x-y diagram at a given temperature for two miscible liquids that form a non-ideal solution, given saturation pressures at that temperature and equations that model the non-ideal behavior of the liquid solution.
  2. Construct a T-x-y diagram at a given pressure for two miscible liquids that form a non-ideal solution, given Antoine equations (saturation pressure versus temperature) for each component and equations that model the non-ideal behavior of the liquid solution.
  3. Determine what phases are present at specified conditions, given a phase diagram.
  4. Calculate bubble points and dew points (both temperature and pressure) using the modified Raoult's law.
  5. Explain the meaning of positive and negative deviations from Raoult's law.
  6. Explain the properties of azeotropes and why they make separations by distillation difficult.