Residual functions of the n-alkane liquids. Part 1.—Corresponding states and congruence

Abstract

The liquid-phase (p^⊖= 1 bar) residual Helmholtz free energy and enthalpy for the n-alkanes C₆ to C₁₀, with benzene and cyclohexane, and the residual Gibbs free energy for the n-alkanes C₆ to C₁₆ are presented as polynomials in (T– 273.15 K), valid up to the normal boiling point. The polynomials for the individual n-alkanes are mutually consistent. At any particular temperature, the standard deviation of each property, plotted against number of carbon atoms (for the n-alkane series) is much smaller than the estimated total uncertainty on individual values. The polynomials, together with those for standard liquid density, are used to show that neither the original two-parameter version of the principle of corresponding states, nor Patterson's generalisation of the version appropriate of the Orwell and Flory equation of state, is applicable to these hydrocarbons. We test also the principle of congruence for binary n-alkane mixtures, using experimental data for n-hexane + n-hexadecane; the principle appears to be valid only as an empirical correlation.