Liquid-State Equation for Normal Paraffins


BASED on measurements of liquid density and of heats of vaporization of the normal paraffin hydrocarbons, a very simple relationship has been deduced that appears to be of general applicability to this family of chemical compounds. The equation is as follows: where ρ is liquid density at the temperature of measurement1; ρc is critical density2; ρ0 is liquid density extrapolated to absolute zero3; (− E/V) is cohesive-energy density of the liquid at the temperature of measurement4; (− E/V)0 is cohesive-energy density of the liquid extrapolated to absolute zero; and α is a constant (= 0.00125 for the n-paraffins).

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  1. 1

    Dornte, R. W., and Smyth, C. P., J. Amer. Chem. Soc., 52, 3546 (1930). Doolittle, A. K., and Peterson, R. H., J. Amer. Chem. Soc., 73, 2145 (1951).

  2. 2

    Critical density values taken from smoothed curve representing results reported by Doss, M. P., “Physical Constants of the Principal Hydrocarbons” (Texas Co., New York, 1943).

  3. 3

    Doolittle, A. K., J. App. Phys., 22, 1471 (1953).

  4. 4

    API Res. Proj. 44, Carnegie Inst. Tech., “Selected Values of Properties of Hydrocarbons”, Table 20m (April 30, 1949) Values at other temperatures interpolated or extrapolated by method described in Hildebrand, J. H., and Scott, R. L., “The Solubility of Nonelectrolyest”, 434 (Reinhold, 1950).

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DOOLITTLE, A. Liquid-State Equation for Normal Paraffins. Nature 174, 369 (1954).

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