A General Equation of State for Pure Molecular Substances,

摘要

The paper describes a new analytic formulation of the thermodynamic properties of a chemically homogeneous,stable molecular substance such as water or carbon dioxide. A mathematical expression for the Helmholtz free-energy function f(v,T) is derived by starting with a form that yields the laws for ideal gases and incorporating into it a series of terms and associated parameters suggested by statistical mechanics and quantum theory considerations. The anomalous behavior of pure substances near the liquid-vapor critical point is also taken into account. This leads to a more comprehensive equation of state applicable to the condensed phases in addition to the gaseous phase. x Accordingly,it is adapted for smoothing as well as interpolating observational data over a wide range of variables. The final result may be regarded as a generalization of van der Waals'equation,modified so as to provide a more faithful representation of high-density measurements and to be consistent with Debye's theory at very low temperatures-and always of course,reducing to the ideal gas law as the density goes to zero. Values for the parameters which enter the approximation via the molecular partition function for the substance are fixed in advance. (Author)