Raoult's Law and Vapor-Liquid Equilibrium: Summary
Key points from this module:
- Raoult's law assumes ideal gases and ideal liquid solution. For similar molecules (e.g., n-hexane and n-octane), Raoult's law may be a good approximation.
- When a vapor mixture is cooled or its pressure is increased, both components condense.
- Bubble pressure is the pressure where the first bubble of vapor forms as the pressure above a liquid decreases at constant temperature.
- Bubble temperature is the temperature where the first bubble of vapor forms as the temperature of a liquid increases at constant pressure.
- Dew pressure is the pressure where the first drop of liquid forms as the pressure of a vapor increases at constant temperature.
- Dew temperature is the temperature where the first drop of liquid forms as the temperature of a vapor decreases at constant pressure.
- Unlike a pure component, at constant pressure a mixture does not evaporate at constant temperature.
After studying this module, you should be able to:
- Given a vapor composition and saturation pressure versus temperature data, determine the dew temperature (at constant pressure) or the dew pressure (at constant temperature).
- Use Raoult's law to calculate equilibrium compositions and/or equilibrium pressures for ideal solutions and ideal gases.
- Construct a pressure-composition diagram for an ideal mixture given saturation pressures at a given temperature.
- Construct a temperature-composition diagram for an idea mixture given Antoine equations at a given pressure.
Prepared by John L. Falconer and Kimberly R. Bourland
Department of Chemical and Biological Engineering, University of Colorado Boulder
Additional screencasts and interactive simulations for vapor-liquid equilibrium of ideal solutions are available on LearnChemE and YouTube