Electrosorption entropy

As a result, the entropy of electrosorption is usually positive. Remembering the well known thermodynamic relationship... 

The major difference between gas phase adsorption and electrosorption is that in the former case adsorption occurs on a bare surface, while in the latter case the metal substrate is solvated, i.e., covered with an adsorbed layer of solvent molecules. Thus it is evident that adsorption on electrodes is a replacement reaction. The observed standard free energy, enthalpy and entropy of adsorption can therefore only be related to the type of interaction between the adsorbate and the electrode if the corresponding thermodynamic quantities for the solvent are known and the number of solvent molecules replaced by each adsorbed organic molecule can be estimated. 

The same relationships also apply to the enthalpy and the entropy of electrosorption. The enthalpy of electro sorption turns out to be less (in absolute value) than the enthalpy of chemisorption of the same molecule on the same surface from the gas phase. On the other hand, the entropy of chemisorption from the gas phase is, as a rule, negative, since the molecule RH is transferred from the gas phase to the surface, losing in the process three degrees of freedom of translation. This is also true for electrosorption, but in this case n molecules of water are transferred from the surface to the solution, leading to a net increase of 3 (n— 1) degrees of freedom. As a result, the entropy of electrosorption is usually positive. Remembering the well known thermodynamic relationship... 

---