This example explains, how you can plot state diagrams (e.g. xy-diagrams as following picture) using the empirical equations of activity coefficients in the application Equilibrium.

There is x the concentration in liquid- and y in the gas phases.

1.9.4.1. Elements

Main Menu: System -> Elements. Selection: C,H,O

1.9.4.2. Compounds

In the window for Gas, Select Compounds C2H5OH(g) and H2O(g)

In the window for Liquid, Select Compounds C2H5OH(l) and H2O(l)

1.9.4.3. Activity Coefficients

Main Menu: System -> Activity Coefficients

Select the logarithmic equations of van Laar in drop-down button as shown in the following picture.

Enter coefficients A and B, press Button Add

Equation 1 is the activity coefficients of ethanol and Equation 2 is the activity coefficient of water in binary mixtures of liquids at 50°C corresponding van Laar

(the constants A and B are given by C.A. Jones, A.P. Schoenborn, Ind. Chem. Eng. 40 (1940) 1273-1276).

1.9.4.4. Record Variables

Main Menu: Monitoring -> Record Definition

Select the concentration of the ethanol and water in liquid and gas phase. You can select also other variables to record

1.9.4.5. Graphic Variables

Main Menu: Monitoring -> Graphic Variables

You can determine, which variables are in which coordinates to show in the Graphic Window.

1.9.4.6. Assignment of the Equations for Activity Coefficients to Substances Ethanol and Water

Enter for activity coefficient of ethanol [1] , and for activity coefficient water [2] in the columns a.c. in the phase table corresponding the definition of the equations for activity coefficients in Chapter 1.9.4.3.

1.9.4.7. Calculation

Main Menu: System -> Calculation by Variation

Insert as variables :

Input Liquid 1 C2H5OH (l) from 0 to 1 with steps +0.01

Input Liquid 1 H2O (l) from 1 to 0 with steps -0.01

Start the calculations.

1.9.4.8. The results of the calculations will be shown in Graphic Window

Enthalpy-concentration diagram of ethanol-water-mixtures

xy-Diagram Ethanol-Water Mixtures

Course of the activity coefficients in ethanol-water mixtures corresponding given data in Chapter 1.9.4.3.