Single-ion heat of transport in electrolyte solutions. A hydrodynamic theory

The standard single-ion heat of transport Q_i*° in electrolyte solutions is derived based on a hydrodynamic approach. It is shown that Q_i*° may be related to the structure and dynamics of the solution through the velocity field induced by the ionic motion and the entropy density of the solvent around the ion. The hydrodynamic approach suggests analogies between the heat of transport and dielectric properties of the solutions. The concepts of the thermal dipole moment and thermal polarization are found to be useful in the discussion of the heat of transport. The hydrodynamic theory permits an analysis of the relationship between the entropy of transport and the entropy of hydration and shows that the entropy of hydration may be obtained from the entropy of transport at the thermodynamic limit. The hydrodynamic expression of Q_i*° also made it possible to carry on a systematic investigation of the Soret effect using the structural and dynamical models of electrolyte solutions. This is illustrated by an example using the Born and Stokes-Einstein models.