Acetonitrile Gibbs free energies

Use the data in Examnie 12.6 to fit the excess Gibbs free energy of the system ethanol/acetonitrile to a Redlich-Kister polynomial with two parameters, obtain equations for the activity coefficients. Use these equations to obtain the activity coefficients at infinite dilution and to construct the Pxy graph of this system at 40 "C. 

Besides bulk free water, there are four types of water bound to adsorbents or bio-objects such as strongly (changes in the Gibbs free energy -AG>0.5-1 kJ/mol) and weakly (-AG<0.5-1 kJ/mol) bound and strongly (5h=4-5 ppm) and weakly (5h= 1-2 ppm) associated waters. This boundary value -AG=0.5-1 kJ/mol depends on system composition and the textural characteristics of the materials. At low amounts of adsorbed water (much smaller than the pore volume), typically all water is strongly bound. A portion of this water can be weakly associated if the pore walls are mosaic (partially modified oxides or hybrid carbon-mineral or polymer-mineral systans) and composed with hydrophilic and hydrophobic patches such as partially silylated silica surface. Adsorbed water clusterization depends also on the presence of co-adsorbates such as chloroform, acetonitrile, DMSO, benzene, etc. 

Vittal Prasad, T. E. Kumar, A. Naresh, S. Prasad, D. H. L. Excess Gibbs free energies of the binary mixtures of acetonitrile with butanols at 94.83 kPa. J. Chem. Thermodyn. 2007, 39, 202-205. 

It is a serious drawback that it is not possible to determine the transfer activity coefficient of the proton (or of any other single-ion species) directly by thermodynamic methods, because only the values for both the proton and its counterion are obtained. Therefore, approximation methods are used to separate the medium effect on the proton. One is based on the simple sphere-in-continuum model of Born, calculating the electrostatic contribution of the Gibb s free energy of transfer. This approach is clearly too weak, because it does not consider solvation effects. Different ex-trathermodynamic approximation methods, unfortunately, lead not only to different values of the medium effect but also to different signs in some cases. Some examples are given in the following log yH+ for methanol -1-1.7 (standard deviation 0.4) ethanol -1-2.5 (1.8), n-butanol -t-2.3 (2.0), dimethyl sulfoxide -3.6 (2.0), acetonitrile -1-4.3 (1.5), formic acid -1-7.9 (1.7), NH3 -16. From these data, it can be seen that methanol has about the same basicity as water the other alcohols are less basic, as is acetonitrile. Di-... 

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