In this screencast I'm going to describe this interactive simulation to better understand
Pxy and Txy diagrams for Vapor Liquid Equilibrium in a binary system.
The simulation is located on the Wolfram demonstration project website and I've given the link here.
Basically the simulation shows two types of plots.
A pressure mole fraction diagram.
And what the simulation allows you to do is change the temperature by moving the slider
on the top and you can also move the black dot around.
So this black dot can be moved with the mouse.
And it can be moved both to change a pressure and the mole fraction.
And then on the right of the plot is the bar graph that represents the fraction of vapor
and the fraction of liquid.
Fraction of liquid is blue and fraction of vapor is green.
And the mole fractions are also indicated on this bar graph.
And so the plot on the left, the green line is the pressure versus the vapor mole fraction.
The blue line is the pressure versus liquid mole fraction.
Benzene is the more volatile component in this simulation and therefore it has a higher
saturation pressure.
It decayed at the saturation pressure the purple circle, saturation pressure for benzene,
and then at the other end the mole fraction of benzene is zero, is the saturation pressure
of the second component.
On the right side is the temperature versus mole fraction again for benzene.
And now the purple circle represents the saturation temperature of benzene for this pressure,
1200 mmHg.
So the saturation temperature is lower for benzene than for the second component.
And again the bar graph on the right represents the relative fractions in the liquid phase
and the vapor phase.
So let's look at the simulation and see how if we changed temperature or pressure and
moved the black dot around, the various mole fractions and amounts in each phase change.
Here in the interactive simulation we are showing a plot of pressure versus mole fraction.
This is at one temperature in this case 93 degrees C. And I can move this dot around.
So I move it at essentially a constant pressure then we don't change the mole fractions in
the vapor and the liquid, but we change the relative amounts as I move to the right, more
vapor and less liquid.
I can change the temperature and what change in temperature is going to do is move the
curves down.
Because remember the intercepts on the y axis correspond to the saturation pressure of each
component.
So the benzene saturation pressure, looks like its about 900 mmHg at this temperature
and then as I lower the temperature, at 70 degrees C it looks like its about 500 mmHg.
And so how these move of course we are just looking at how the saturation pressures change
and then this blue like is pressure versus mole fraction in the liquid phase.
And that's linear where the end points are the saturation pressure.
The corresponding Txy diagram also allows you to move with your mouse, move the black
dot around and change the fractions.
And of course also change the temperature.
Move it into all vapor.
And then I can increase the pressure because this is constant pressure.
If I increase the pressure than the curves move up because at higher pressure requires
higher saturation temperature.
Again the y intercept corresponds to saturation temperature for pure components.
And the bar graph shows relative amounts of liquid and vapor.
So hopefully by using these interactive simulations you can get a better physical understanding
of vapor liquid equilibrium for a binary solution.