Electrostatic energy, variation with dielectric constant

The over-riding significance of gas-phase measurements is that in the gaseous state the contributions of electrostatic and even of London dispersion forces can be reasonably estimated this allows of more significant comparison with the observed AH values. At this point it may be appropriate to emphasize the variation in AH with the medium in which it is observed. If the free energy increase (AG) attending the dissociation of the dimer were to vary with the dielectric constant (D) according to... 

As indicated in the preceding sections, evaluation of electrostatic energies requires knowledge of electrostatic potential for a given charge distribution. The Poisson equation relates spatial variation of the potential < ) at position r to the density of the charge distribution p, in a medium with a dielectric constant e ... 

The exponential term is the ratio of the electrostatic to thermal energy, with a the distance at which the ions can be considered paired, k is Boltzmann s constant, and e is the average dielectric constant of the solvent ave- The ion size parameter a is a constant with temperature showing little variation with solvent. The variation of Ki does depend on the variation of the dielectric constant(s) with temperature. Once the values for a, e(T), m(T), and /x (orientation) are known for a given solute/solvent system, the current as a function of temperature and concentration may be considered determined. Experimental and calculated results for the system tetra-iso- pentyl ammonium bromide in a mixed solvent containing compounds of alkoxy benzylidine-p-amine phenyl esters (APAPA family) re shown in Fig. 5. 

---