The Thermodynamics of Chromatography - Interactions Between the Atoms of Hydrogen, Carbon, Chlorine and Bromine and an Exclusively Dispersive Stationary Phase > Experimental Data > Page 34

Table 2. (DG') Values for the Elements Hydrogen, Carbon, Chlorine and Bromine from Retention Data for Some Substituted Methanes

Element  (DG') 20˚C  (DG') 30˚C  (DG') 40˚C  (DG') 50˚C
Hydrogen 0.189 0.170 0.155 0.139
Carbon 0.314 0.295 0.269 0.247
Chlorine 0.594 0.556 0.523 0.490
Bromine 1.006 0.949 0.897 0.848

The values obtained for the different parameters were also calculated using equations (9) to (18) and the calculated data are included with those experimentally determined in table 1.

Having evaluated the contribution of each atom to log(K) the standard enthalpy and standard entropy of each interacting atom can now be assessed.

Now,                         RT ln (K)  =  -DGo

                    

and                                   

where (DHo) is the standard enthalpy change,
    and (DSo) is the standard entropy change.