Articulo equacion van der walls

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  • Publicado : 19 de febrero de 2010
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In typical physical chemistry courses the students told how the van der Waals equation works. The mathematics need for making a Maxwell constructionis difficult for the average chemistry student (what is needed are the roots of a cubic polynomial). This make it difficult to show how the liquid-gas phase diagram is obtained from the equation ofstate.

Here a spreadsheet experiment is presented that can be used to illustrate various aspects of the van der Waals equation of state. With this spreadsheet, the students are able to play aroundwith the van der Waals equation so that they can see how this equation works. Together with this spreadsheet, supporting materials is presented that includes a set of questions that enable the studentsto study actively these topics:

1 The critical pressure, temperature and volume

2 The difference between isotherms of the ideal gas and the van der Waals fluid at high temperatures.

3The van der Waals loop

4 The Maxwell construction and the coexistence curve in the p-v phase

5 The Maxwell construction and the liquid-vapor line in the p-T phase diagram

6 The law ofcorresponding states

7 A comparison of the predictions of the van der Waals equation to experimental data.

In order to answer the questions presented in the supporting material, the studentshave to make their own plots.

This spreadsheet experiment can be used as an integrated part of a physical chemistry course that includes lectures, experiments, and workgroups. Typically the students,working in groups of 2, need approximately 2 to 2,5 hours (break included) to answer the questions. This spreadsheet is also for self-study.

This spreadsheet is designed for Excel. It runs also onOpen Office spreadsheet Calc (Version 2.0).

ACKNOWLEDGEMENT

It is a pleasure to thank Dr. T. van der Berg and Dr. J. Knuiman for discussions about this project. A referee is thanked for...
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