Chapter 2, Lesson E - Ideal Gas and Graphical Equations of State

In this lesson, we studied the Ideal Gas EOS and the Generalized Compressibility EOS. We showed that any two of the three variables P, V and T we could use an EOS to determine the value of the unknown parameter.

We started by refreshing your memory about the Ideal Gas EOS and we reformulated it in terms of for all the reasons discussed in Lesson B. Next, we focused on defining conditions under which using the Ideal Gas EOS is acceptable. In general, if the molar volume estimated using the Ideal Gas EOS is greater than 20 L/mole, then it is acceptable to treat the gas as an ideal gas.

When the Ideal Gas EOS is not applicable, the Generalized Compressibility EOS can be used to solve the P-V-T problem to within an accuracy of about 1%. The key to this method is the compressibility factor, Z , which is the ratio of the real molar volume to the molar volume estimated using the Ideal Gas EOS. The Principle of Corresponding States lets us use the Generalized Compressibility Charts (based on experimental data) to determine Z from two out of the three reduced properties: TR, PR and . Finally, we use the value of Z obtained from the charts to estimate the value of the unknown parameter: T, P or . Be careful reading the charts. If you do not read Z correctly the accuracy of the method will be lost.

In the next lesson, we will learn how to use sophisticated, computer-friendly EOS's to solve P-V-T problems.