Date on Master's Thesis/Doctoral Dissertation


Document Type

Master's Thesis

Degree Name

M. Eng.


Chemical Engineering

Committee Chair

Collins, Dermot Joseph


Equations of state


Equations of state attempt to describe the relationship between temperature (T), pressure (P), and molar volume (v) for a given substance or mixture of substances. The ideal gas law is the simplest form of an equation of state. An ideal gas can be considered as a large quantity of small molecules that have no friction, no attractive or repulsive forces. The ideal gas law is a reasonable approximation at low pressures and high temperatures, but not at higher pressures and lower temperatures. Thus, better methods for predicting real gas behavior have been continuously introduced over the past 200 years. Another approximation is to assume that gas atomes and molecules behave as hard spheres. These spheres are incompressible and only repulsive forces are significant at the moment of collision. A recent modification made to the van der Waals equation of state (VDW) incorporates the hard sphere model, giving better representation of the van der Waals parameters over a broader temperature and pressure range. The efficacy of this modified van der Waals equation of state was assessed for six previously researched compounds -ethane, propane, n-butane, n-pentane, argon and water. Physical property charts (specifically molar volume and molar enthalpy charts) were developed for these substances using the original VDW and modified VDW, as well as the Redlich-Kwong (RK) and Redlich-Kwong-Soave (RKS) equations of state. Results for molar volume revealed that for the four hydrocarbons, the modified VDW compared best with the given experimental data, but not for argon and water. Results for molar enthalpy showed the original VDW compared more favorably with experimental data that the original VDW, but not as well as the RK equation of state.