Enthalpy aqueous clusters

One of our important contributions in the field of aqueous clusters has been to provide quantitative estimates of the effects of anharmonicity on zero point vibrational energies (ZPVE) and thermodynamic energies at finite temperatures [41]. For the water dimer, MP2/[13s8p4d2f/8s4p2d] calculations yielded values of enthalpy (AH = —3.19kcal/ mol), free energy (AG = 3.39 kcal/mol), and entropy (AS = —17.7 cal/moI/K) at 373 K, which are well within the experimental bounds (A//=—3.59 0.5 kcal/mol. 

M. D. Tissandier, K.A. Cowen, W.Y. Feng, E. Gundlach, M. H. Cohen,A. D. Earhart, J. V Coe, T. R. Tuttle Jr. The Proton s Absolute Aqueous Enthalpy and Gibbs Free Energy of Solvation from Cluster-Ion Solvation Data. J. Phys. Chem. A 1998, 102, 7787-7794. 

Fig. 5-4. Schematic one-dimensional enthalpy diagram for the exothermic bimolecular Finkelstein reaction Cl -I- CFI3—Br Cl—CH3 -I- Br in the gas phase and in aqueous solution [469, 474, 476]. Ordinate standard molar enthalpies oi (a) the reactants, (b, d) loose ion-molecule clusters held together by ion-dipole and ion-induced dipole forces, (c) the activated complex, and (e) the products. Abscissa not defined, expresses only the sequence of (a). ..(e) as they occur in the chemical reaction.

In Sec. 2.5, we introduced two 1-D models for water. The two models are almost equivalent in their capacity to unveil the molecular reasons for the outstanding properties of liquid water. Extending the application of these two models for aqueous solutions shows that while the primitive model fails to show large negative anomalous entropy and enthalpy of solvation of inert solutes, the primitive cluster succeeds. The reason is that the entropy and enthalpy of solvation of a solute in water are due to the capability of the solute to induce structural changes in the solute. In the TD primitive model, one could not achieve that effect, not because of any deficiency of the model but because of the assumption of nearest-neighbor interactions only. 

Figure 3.27 shows the dependence of Xi (the mole fraction of the monomeric water particles) as a function of the mole fraction of the solute The behavior of Xi as a function of 5 is unique in the sense that initially at low values of ys, Xi decreases. This means that monomers are used to build up clusters. As we shall see below, this behavior is typical for aqueous solutions and is part of the explanation for the unusually large negative entropy and enthalpy of solvation of the solute. At higher concentrations of the solute s, the concentration of all... 

Hill T (1960) An introduction to statistical thermodynamics. Addison-Wesley, Reading Tissandier MD et al (1998) The proton s absolute aqueous enthalpy and Gibbs free energy of solvation from cluster-ion solvation data. J Phys Chem A 102(40) 7787-7794 Kelly CP, Cramer CJ, Truhlar DG (2006) Aqueous solvation free energies of ions and ion-water clusters based on an accurate value for the absolute aqueous solvation free energy of the proton. J Phys Chem B 110(32) 16066-16081... 

Farges F, Sharps JA, and Brown GE (1993) Local environment around gold(III) in aqueous chloride solutions anEXAFS spectroscopy study. Geochim. Cosmochim. Acta 57 1243-1252 Feller D, Glendening ED, de Jong WA (1999) Structures and binding enthalpies of lvr(H20)n clusters, M = Cu, Ag, Au. J ChemPhys 110 1475-1491... 

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