The Behavior of Gases
This chapter compares the behavior of real gases and ideal behavior. The differences between the two are mainly related to the atomic or molecular interactions of real gases. Although knowledge of the physical properties of a real gas is not required in a thermodynamic examination of the gas, an appreciation of the origin of the physical properties provides a better understanding of the thermodynamic behavior. Before discussing the thermodynamic properties of mixtures of ideal gases, it is necessary to introduce the concepts of mole fraction, partial pressure, and partial molar quantities. This chapter explains these concepts in more detail. The deviation of a real gas from ideal behavior can be measured as the deviation of the compressibility factor from unity. The chapter shows that at any temperature, the molar Gibbs free energy of an ideal gas is a linear function of the logarithm of the pressure of the gas.