Facts at your Fingertips: Pressure Measurement for Real Gases
By Scott Jenkins |
The ideal gas law ( PV = nRT), relating molar volume of a gas to pressure and temperature, is predicated on two assumptions: 1) that the volume occupied by the gas molecules is negligible compared to the volume of the vessel; and 2) that no intermolecular attractive forces are present. In reality, these assumptions limit the applicability of the ideal gas law, especially at higher pressures and densities, and low temperatures. For accurate calculations of PVT behavior of real gases in industrial settings, engineers have developed many equations of state (EoS) for various conditions. This reference provides information on several key cubic equations of state that attempt to accurately predict real gas behavior.
Van der Waals equation
In 1873, Dutch physicist Johannes D. Van der Waals noted the non-ideality of gases and proposed modifications to the ideal gas law that addressed the size of gas molecules and accounted for the strength of the mutual attraction among them. He introduced the two constants (a and b) to the ideal gas law to correct for intermolecular attractive forces (a) and for finite molecular size (b) (Equation (1)). The coefficients a and b are characteristic of each individual gas and were determined experimentally…