Raoult's Law and Vapor-Liquid Equilibrium: Interactive Simulations

Simulation: Visualization of Vapor-Liquid Equilibrium in a Binary Mixture

This simulation visualizes the behavior of a binary mixture in vapor-liquid equilibrium. The number of molecules, relative volatility, and liquid composition can be adjusted with sliders. The bar graphs represent the mole fractions of each phase. The number of particles and their speed are not meant to correspond the actual physical values, but merely to demonstrate the differences in compositions between phases. The relative densities correspond to a binary mixture at high pressures.

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

  1. For a relative volatility of 2.0 (blue/green), and a liquid mole fraction of 0.50, when the liquid mole fraction increases for blue molecules, does the vapor mole fraction of blue molecules increase or decrease?
  2. For a relative volatility of 2.0, and a liquid mole fraction of 0.50, when the relative volatility (blue/green) increases , does the vapor mole fraction of blue molecules increase or decrease?
Simulation: P-x-y and T-x-y Diagrams for VLE

The vapor-liquid equilibrium (VLE) behavior of a benzene (C6H6)/toluene (C7H8) mixture is demonstrated in P-x-y and T-x-y diagrams. The blue line represents the liquid-phase boundary (bubble point) and the green line represents the vapor-phase boundary line (dew point). Drag the black dot on either diagram and the bar chart shows the amounts of liquid (blue) and vapor (green); the system contains a total of 1 mol. The mole fractions of benzene in each phase (xB for liquid phase, yB for vapor phase) are also shown in the bar graph. Use sliders to vary the temperature for the P-x-y diagram and the pressure for the T-x-y diagram. This system is modeled by Raoult’s law because a benzene/toluene liquid phase is expected to be ideal.

Try to answer these questions before determining the answer with the simulation. We suggest that you write down the reasons for your answers.

  1. When the temperature increases, what happens to the two curves in the P-x-y diagram? Do they move to higher or lower pressure or do they not change? Why?
  2. If the black dot moves at constant overall composition to higher pressure at constant temperature in the P-x-y diagram, do the mole fractions of the liquid and vapor phases increase or decrease or does one increase and one decrease?
  3. How is the T-x-y diagram different from the P-x-y diagram?