ABSTRACT
The knowledge of thermodynamic properties such as internal energy, enthalpy, free energy, entropy, and Helmholtz free energy is important in the design and use of any substance in practice. For ®uids, these properties are usually evaluated from measurements of molar volume as a function of temperature and pressure, yielding, pressure-volume-temperature (PVT), relations which may be expressed mathematically as equations of state. For small molecules such as a monatomic gas, it has been found that the ideal gas law is a good representation of the PVT behavior. The ideal gas law can be written as
PV nRT= . (2.1)
where P is the pressure with units of Nm−2; V (m3) is the volume; R is the universal molar gas constant (Jmole−1K−1); n is the number of moles of the substance; and T (K) is the temperature. The ideal gas law can be derived as follows.
