Thermodynamic Parameters of Adsorption on Heterogeneous Surface

An important result is that the effective desorption energy for the heterogeneous surfaces depends on temperature Nevertheless, let us for a while abandon it and suppose that jjet does not depend on temperature. Another assumption will be that the entropy change is the same for all partial isotherms, independent of EA. Then we take into account Eq. 5.3 for the experimental constant of adsorption and move to the characteristics of desorption from heterogeneous surfaces. It follows that the measurements yield an equilibrium constant, which is to be interpreted as the entropy factor multiplied by the expectation value of the desorption energy factor  

Let us apply the simplest form of van t Hoff s equation to the data from various distributions of E given in Table 5.4. Notice that if Eq. 5.72 is valid, then the ratio of the equilibrium constants equals that of the desorption energy factors calculated from 5.71. Then the Second Law value of the effective jet would come from  

The results are in the last column of Table 5.4. They show that employing the Second Law procedure gives higher values of jjet than the calculations based on the knowledge of p ( (j). It is an interesting observation which deserves more attention. 

Another possible approach to the evaluation of the required effective quantities is to start with the effective entropy change. Hill [98,99] considered the statistical mechanics of the localized unimolecular adsorption on heterogeneous surfaces to propose formulae for the configurational entropy. 

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