The Thermodynamics of Chromatography - Thermodynamics Basics > Page 3

Thus, the standard energy change is made up of an actual energy or standard enthalpy change resulting from the intermolecular forces between solute and stationary phase and a standard entropy change that reflects the resulting restricted movement, or loss inrandomness, of the solute while preferentially interacting with the stationary phase.

From, equations (1) and (2), substituting for (DGo )

                       RT ln (K)  =  -DGo = -DHo+ TDSo

            Thus,                               (3)

 

 or                                                  (4)

It might be assumed from equation (3) that it would be relatively easy to calculate the retention volume of a solute from the distribution coefficient, which, in turn, could be calculated from a knowledge of the standard enthalpy and standard entropy of the specific distribution. However, the thermodynamic properties of a distribution system are bulk properties, and as such, they represent, in a single measurement, the net effect of a number of different types interactions which, at the present time (except for dispersive interactions) are almost impossible to separate, identify and assess quantitatively.