The consideration of the evaporating and condensing molecules’ interaction with the surface layer of nonassociated liquids made it possible to find an equation for relations between the saturated vapor pressure , from one side, and surface tension, critical temperature, and molar volume of the liquids, from the other side. This equation takes into account the influence of intramolecular conformational transitions of evaporating molecules on the quantity of their energy barrier. There are two types of the condensation process for the nonassociated liquids: soft and hard molecular condensation. For some vapor molecules the surface layer of the liquids behaves as an impenetrable elastic film. In the case of evaporating molecules, their one-particle potential barrier caused by the surface molecules vibration is essentially higher for the conformationally flexible molecules than that for rigid ones. 1. Introduction For nonassociated liquids in the state of phase equilibrium with their saturated vapor, both evaporation and condensation are responsible for the level of the vapor pressure. In its turn, the saturated vapor pressure of liquids ( ) is related also to the intensity of molecular motion (i.e., molecular kinetic temperature) therein. And really, any increase in absolute temperature of a liquid leads to the corresponding increase in the motion intensity, when the number of molecules evaporating per unit time from the unit surface (and, therefore, value of ) grows [1]. Usually the dependence of on can be described by means of the following equation (Antoine’s equation [2]): In (1) , , and are some constants which differ for various liquids. As a rule, for any liquid these constants are being defined on the basis of its experimental values. Other numerous correlations between and are similar to (1), and they are formed by means of various additional addenda depending on to its right-hand side (see [3]). However, any above-mentioned correlation applied to the calculation of for a new liquid requires the definition of its own new constants depending on the nature of this new liquid. Furthermore, it is well known that molecules of any liquid can be divided into two groups, according to the value of their one-particle kinetic energy [1]. The first group includes the so-called “hot” molecules. Their kinetic energy is greater than or equals to some critical for jumping value . The molecules of the second group stay in their potential wells caused by the intermolecular attractive forces between these molecules. The given molecules take part in their vibration
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