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More Sophisticated EOS's

Equations of State that we studied in the previous lesson:

1. Ideal Gas

2. Generalized Compressibility Factor

More sophisticated Equations of State that we will study in this lesson:

1. Virial EOS

2. Van der Waals EOS

3. Redlich-Kwong EOS

4. Soave-Redlich-Kwong (SRK) EOS

Lesson 2F: page 1 of 10

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Ch2, Lesson F, Page 1 - More Sophisticated EOS's

In the previous lesson, we learned a method to help us decide whether the Ideal Gas EOS is accurate for a given state.
We also learned to use the Generalized Compressibility Factor EOS when the Ideal Gas EOS was not applicable.
The problem is that the Generalized Compressibility Factor EOS is not well suited to iterative or computer aided calculations.
Other more sophisticated EOS’s have been developed that are NOT graphical in nature.
These more sophisticated EOS’s allow us to take advantage of the power of computer programs such as Excel to solve involved problems that require repeated use of an EOS.
Some of these equations of state can be used to describe vapor-liquid equilibrium and to predict a variety of thermodynamic properties of liquids and gases. But these applications of the EOS’s are beyond the scope of this course.
In this lesson, we will consider 4 EOS’s.
We begin with the Virial EOS because it is based on the Ideal Gas EOS and it was one of the first EOS’s to improve on the Ideal Gas EOS.
Next we will study the Van der Waal’s EOS. This was the first cubic EOS and it the set the stage for many cubic EOS’s that followed.
One of best cubic EOS’s is the Redlich-Kwong EOS. It is commonly used to predict the PVT of a wide variety of non-polar gases.
We will wrap up with the Soave-Redlich-Kwong EOS. This EOS is a slight modification of the RK EOS that yields better accuracy for hydrocarbon systems.
It is important to note that none of these EOS’s are very accurate for polar molecules, especially at smaller molar volumes.
Water is the perfect example. Specialized EOS’s have been developed just for water ! These specialized EOS’s are beyond the scope of this course. When you need to know the thermodynamic properties of water, I recommend that you access the NIST website.
OK, now we are ready to dive into the Virial EOS.

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