A thermodynamic theory of the Soret effect in a multicomponent liquid

A phenomenological theory of the Soret effect in a multicomponent mixture is presented. The theory is applicable to mixtures in which the Soret effect is determined mainly by the energetic interaction between the molecules, such as liquids and dense gases, and it is based on the assumption that the steady state has a maximum number of possible microstates. The equations derived for the separation enable the thermal diffusion factor αT of each component to be calculated using only an equation of state for the mixture and the standard state enthalpy. With a sufficiently accurate equation of state, the calculated αT values correspond well with the data on measured αT values of liquids and dense gases and show a better correspondence than Haase’s theory. The method presented may be applicable to other coupled transport phenomena in the steady state.