Vapor-Liquid Equilibrium For Non-Ideal Solutions: Interactive Simulations

These simulations were prepared using MathematicaDownload the free CDF player, and download the simulation CDF file (link below). Predict the behavior when a parameter changes before using a slider to change that parameter. For one of these simulations, a screencast is provided to explain how to use it.

Simulation: Vapor Pressure of Binary Solutions

Most solutions exhibit deviations from Raoult's law. For a positive deviation, the bubble pressure is greater than that predicted by Raoult's law and indicates that the attractive interactions between A and B molecules are weaker than the attractive interactions between A-A and B-B molecules. A negative deviation means the bubble pressure is smaller than that predicted by Raoult's law, implying stronger mutual interactions between unlike molecules. The blue and green curves represent the partial pressures of A and B, respectively, and the black curve shows the total vapor pressure. The dashed lines refer to the hypothetical ideal behavior of the corresponding vapor pressures.

This simulation is by S. M. Blinder

Try to answer this question before determining the answer with the simulation:

1. As the positive deviation from ideality increases, does the partial pressure of component B deviate more from Raoult's law behavior at low or high values of xB? This demonstration presents P-x-y and T-x-y diagrams for vapor-liquid equilibrium (VLE) of a benzene/ethanol mixture. Drag the black dot to change the benzene mole fraction and the temperature or pressure. This liquid mixture is non-ideal and the system has an azeotrope at the conditions used. The bar chart displays the relative amounts of liquid (blue) and vapor (green) in equilibrium and the mole fraction of benzene in each phase. The blue line represents the liquid-phase boundary (bubble point), and the green line represents the vapor-phase boundary (dew point).

Try to answer these questions before determining the answer with the simulation:

1. This system has a maximum-pressure azeotrope. Does it have a minimum- or maximum-temperature azeotrope?
2. If the temperature increases, how does the azeotrope change? Does its pressure increase or decrease?