Helmholtz energies from equations of state and their relative deviations

摘要

Extension of the hard-sphere equations of state to non spherical hard-body systems represents a formidable task. For an equation of state that is applicable to liquid and vapor states (and explicit for pressures), the corresponding characteristic function is the residual energy. The equations of state of Carnahan Starling, Boublik and R J Sadus are used to derive an expression for residual Helmholtz energies. Relative deviations of residual Helmholtz energies for these equations of state have been reviewed. The deviations of compressibility factor against packing fraction have been plotted for these equations of state. The agreement of these plots is found to be good for lower n-alkanes but not for longer n-alkanes. Thus it becomes obvious that the compressibility factor depends considerably on the shape of the studied molecules.