Energy curves water adsorbed

Figure 6.10. Schematic potential energy curve for adsorbed water and its dissociation products.

Extrapolation of the AG = /(C ) curves to the water free energy axis enable us to estimate the maximum magnitude of variations in the free energy of water caused by adsorption (AG, i,x). The AG ux value determined in accordance with this method and the data for the free surface energy calculated using Eq. (2) are listed in Table 8. The values of maximum water layers thickness (t/ " ) perturbed by the surface, calculated on the basis of the Cw " value, are also listed in Table 8. These data permit us to conclude that the free surface energy for the adsorbents studied increases in the following order ... 

Figure 2. NMR relaxation times for water adsorbed on porous glass (a) sample 2 at P/Po = 0.4 (b) sample 5 at P/P 0.62 ( ) experiment (—) theory curves a and b least-squares fit to the Resing model (21) curve c obtained by using the parameters derived from the least-squares fit to adjust the Ta behavior at high temperatures to produce a shoulder effect caused by the presence of high energy...

The simulations suggest the following picture for an ion transfer reaction before the reaction the ion is located in a weak adsorption site, where it is separated from the electrode by one layer of water molecules. As the ion approaches the electrode surface it displaces water from the surface and partially looses its solvation shell this requires a substantial energy of activation. Subsequently, the ion moves down the free energy curve towards an adsorption site on the metal surface simultaneously the electronic interaction with the metal increases, electron exchange becomes adiabatic, and the adsorbed particle carries a partial charge (see next section). 

The diabatic free energy curves for the adsorption of and I near Pt(lOO) were calculated. is the energetically favorable species in solution, while the more stable species on the surface is I . The crossing between the two diabatic curves occurs at short distances, when the ion has already penetrated the adsorbed water layer. 

The solvent free energies for an ET reaction between two charge transfer centers adsorbed at the water/l,2-dichloroethane interface were investigated by MD simulations. The charge centers were modeled as Lennard-Jones spheres with the parameters a = 5A and e = O.lkcal/mol. In bulk water, the free energy curves calculated from the molecular dynamics simulations are approximately well described by paraboli. While the curvature of the free... 

The interaction between the adsorbed molecules and a chemical species present in the opposite side of the interface is clearly seen in the effect of the counterion species on the HTMA adsorption. Electrocapillary curves in Fig. 6 show that the interfacial tension at a given potential in the presence of the HTMA ion adsorption depends on the anionic species in the aqueous side of the interface and decreases in the order, F, CP, and Br [40]. By changing the counterions from F to CP or Br, the adsorption free energy of HTMA increase by 1.2 or 4.6 kJmoP. This greater effect of Br ions is in harmony with the results obtained at the air-water interface [43]. We note that this effect of the counterion species from the opposite side of the interface does not necessarily mean the interfacial ion-pair formation, which seems to suppose the presence of salt formation at the boundary layer [44-46]. A thermodynamic criterion of the interfacial ion-pair formation has been discussed in detail [40]. 

The situation is quite different in the case of an acetic acid-water system. The energy of acetic acid adsorption on platinum is low and therefore the voltammetric curves taken in the absence and in the presence of acetic acid in the supporting electrolyte are nearly the same. However, radiometric data show that C-labeled acetic acid is adsorbed on the electrode surface. Most likely the acetic acid molecules are adsorbed on the top of the water molecules populating the electrode surface. Simultaneously recorded voltammetric and counting rate data are shown in Fig. 8. 

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