Details

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 [1] explains how to use this Demonstration.

Reference

[1] 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.