The Thermodynamics of Chromatography - Interactions Between the Atoms of Hydrogen, Carbon, Chlorine and Bromine and an Exclusively Dispersive Stationary Phase > Experimental Data > Page 37

 

 

Figure 14 Graph of Standard Entropy against Standard Enthalpy for Each Element

A negative value or (DHo) means that heat is evolved when interaction takes place in the stationary phase as a result of the forces between the atom and the n-octadecane. From table 3 it is seen that the standard entropy term increases with the standard enthalpy term. This relationship between standard entropy and standard enthalpy  is shown in figure 14.

  

 

It is seen that there is an impressive clean linear correlation between (DHo) and (DSo) (index of determination 1.000). The excellent correlation is due to the condition that only one interactive process is significantly active in the distribution (i.e., dispersive interactions). As already discussed, a linear relationship between standard enthalpy and standard entropy is to be expected. An increase in enthalpy indicates that more energy is used up in the interaction of the atom with the molecules of the stationary phase. This means that the inter-atomic/molecular forces are stronger and, thus, the stationary phase molecules hold the atoms more tightly. In turn, this will reduce the freedom of movement  and random nature of the atom which will result in a corresponding reduction in standard entropy.