Dependence of Surface Tension on Temperature

It is shown that the equation of Reiss et al. for the surface tension of liquids composed of hard-core molecules does not usually provide the proper dependence of surface tension on temperature for typical non-ionic liquids. Because of this, an empirical computation procedure is adopted, whereby the hard-core diameter is given a temperature dependence similar to that of the collision cross section for gas viscosity. When Lennard-Jones 6–12 or Sutherland intermolecular-potential data are then used to calculate a hard-core diameter, the agreement between computed and measured dependence of surface tension on temperature is usually very good, even for liquids composed of such polar, aspherical molecules as water, ethanol, and ammonia. As an illustration of the potential value of the empirical use of gas-viscosity data for improving computations of the dependence on temperature of physical properties and thermodynamic values for liquids, the Lennard-Jones 6–12 and Sutherland data are applied to two rigid-sphere relationships for liquid compressibility.