Examination of the statistical rate theory expression for liquid evaporation rates

Abstract

Recent measurements of the temperature at the interface of an evaporating liquid have been found to be in conflict with the predictions of classical kinetic theory. Under 20 different experimental conditions for water evaporation, the temperature in the vapor at the interface was measured to be greater than that in the liquid at the interface and this relation between the interfacial temperatures is the opposite to that predicted from classical kinetic theory. When these same data were used to examine the statistical rate theory (SRT) expression for the liquid evaporation rate, almost complete agreement was found. This theoretical approach is based on the transition probability concept, as defined in quantum mechanics, a hypothesis that assumes the rate of exchange between the possible quantum mechanical states of an isolated system that are within the energy uncertainty has the same value, and the Boltzmann definition of entropy. To determine whether the SRT expression for the evaporation rate also describes the liquid-vapor phase transition for liquids other than water, two hydrocarbons have been examined. The agreement between the predictions from SRT and the measurements is equally as good. These results raise the question of whether a quantum mechanical description is essential to describe the condition existing at the interface of an evaporating liquid.