Adding a Second Component to a Single-Component Vapor-Liquid Equilibrium (VLE) Mixture
Initially, 20 mol of liquid and 0.1 mol of vapor are in equilibrium in a cylinder with a movable piston. The system initially contains only -hexane and -octane is injected when the inject isothermally play button is pressed, or it starts with -octane and -hexane is injected. Change the number of moles injected at constant temperature and pressure with a slider. The system is modeled by Raoult’s law. The -- diagram explains why the final state is all liquid or all vapor. Use the reset button to start the process again.
Contributed by: Rachael L. Baumann (August 2014)
Additional contributions by: John L. Falconer and Nick Bongiardina
(University of Colorado Boulder, Department of Chemical and Biological Engineering)
Open content licensed under CC BY-NC-SA
The system is modeled by Raoult's law. The -- diagram shows the behavior when one component is added to the mixture.
The saturation pressures (bar) of -hexane and -octane are calculated using the Antoine equation, where , and are constants, and is temperature (°C):
Vapor-liquid equilibrium for this ideal system exists when . When the system initially contains -hexane in vapor-liquid equilibrium and -octane (which has a lower saturation pressure) is added at constant total pressure and constant temperature, then , so only liquid is present at equilibrium. When the system initially contains -octane in vapor-liquid equilibrium and -hexane (which has a higher saturation pressure) is added at constant total pressure and constant temperature, then , and only vapor is present at equilibrium.
The screencast video at  explains how to use this Demonstration.
 Adding a Second Component to a Single-Component Vapor-Liquid Equilibrium (VLE) Mixture [Video]. (Dec 16, 2020) www.learncheme.com/simulations/thermodynamics/thermo-2/adding-a-second-component-to-a-single-component-vle-mixture.