Equilibrium Curve (constant pressure)

The Figure below (left) showed a typical equilibrium curve for a binary mixture on x-y plot. It contains less information than the phase diagram (i.e. temperature is not included), but it is most commonly used. It is useful for graphical design in determining the number of theoretical stages required for a distillation column.

NOTE: Remember that up till now we are looking at ideal solutions only. Phase diagrams and equilibrium curves of other shapes and characteristics are available. See for example the middle and right Figures above. These occur when there is a deviation from ideal solution behavior.

Click here for examples of equilibrium curves.

Equilibrium curve for any binary mixture can be obtained from the corresponding phase diagram. Click here for more details.

In the above analysis, the pressure is assumed constant. When the pressure is changed, the entire VLE is changed as well. Click here to see the effect of increased pressure on the phase diagram and equilibrium curve.

[Reference: "INTRODUCTION TO CHEMICAL ENGINEERING", CHAPTER 13, E.V. Thompson & W.H. Ceckler, McGraw-Hill, 1978]