On the Natyre of the Influence of the Architecture of Molecules on the Thermophisical Properties of Alkane Isomers

Abstract

Purpose. Performing measurements of sound velocity and density in the liquid phase of hexane isomers on the saturation line in a wide range of state parameters, including the critical region.Methods. Using a precision pulse-phase method for measuring the speed of sound in the liquid phase of hexane isomers and their density with a pycnometer at atmospheric pressure. The paper discusses the results of precision measurements of sound velocity and density in five hexane isomers. The speed of sound was measured on the equilibrium curve in the liquid phase of isomers by the pulse-phase method in the range from -30 to their critical point. The measurement error of the speed of sound did not exceed 1 m/s. Density measurements were performed using a pycnometer at atmospheric pressure in the range from -30 to their normal boiling point with an error not exceeding 0.05%. The results of sound velocity and density measurements were used to study the character of intermolecular forces. The necessity of taking into account the non-covalent chemical interaction of molecules of the studied substances is shown.Results. Sound velocity measurements were performed on the saturation line in the liquid phase of all five hexane isomers in the temperature range from -30 C to the critical temperature of all 5 isomers. The obtained results are used to study the features of the dependence of the energy of intermolecular forces on the parameters of the state in the field of research.Conclusion. It is shown that the energy of intermolecular forces in marginal hydrocarbons and other simple substances is the sum of 3 terms representing: 1) the energy of the dispersive attractive forces proportional to the square of the density; 2) the energy of the repulsive forces proportional to the biquadrate of the density and 3) the energy of weak chemical non-covalent binding forces proportional to the cubic root of the density of matter.