Chem.Eq.Diagr  Chemical Equilibrium Diagrams / Tutorials

Make diagrams for constant gas pressure:

log PCO2 = constant

Follow these simple steps:

1) Start DATABASE and click on “C” (carbon) in the periodic table. Click on “CO3 2−” in the list of available components. Both “H+” and “CO3 2−” will be listed as selected components. Click on the pull-down menu “File / Save and Exit”. Click on the SPANA button to save the data file and to make a diagram. Enter a file name, for example CO3 2-”.

2) The SPANA main window will appear. Diagrams made with these chemical components (H+ and CO32−) would have a total concentration for carbonate (example with [CO32−]T = 10 mM). A diagram for constant logPCO2 requires that CO2(g) is one of the chemical components. It is necessary to exchange a component with a reaction products.

Click on the pull-down menu “Run / Modify chemical system”. The “modify” window appears. Click on “CO3 2-” to select it. Click on the “Exchange” button: Exchange button

A new window will appear listing the available reaction products. Click on “CO2(g)” to select it and on the OK-button. Back on the “modify” window click on the “Save changes and exit” button. Give a name for the new data file, for example “CO2(g)”.

Back on the SPANA main window: click on the pull-down menu “Run / Make a Diagram”. A new window appears to select what type of diagram is wanted. Click on the Diagram button in the upper-left corner of the window.

Diagr_Button

The calculations will be done by a console program. When the calculations are finished the diagram is displayed in a window:

Diagr LogCO2

Compare this diagram with that obtained when CO32− is a component instead of CO2(g).