Huckel calculations ionic reactions

The input of the problem requires total analytically measured concentrations of the selected components. Total concentrations of elements (components) from chemical analysis such as ICP and atomic absorption are preferable to methods that only measure some fraction of the total such as selective colorimetric or electrochemical methods. The user defines how the activity coefficients are to be computed (Davis equation or the extended Debye-Huckel), the temperature of the system and whether pH, Eh and ionic strength are to be imposed or calculated. Once the total concentrations of the selected components are defined, all possible soluble complexes are automatically selected from the database. At this stage the thermodynamic equilibrium constants supplied with the model may be edited or certain species excluded from the calculation (e.g. species that have slow reaction kinetics). In addition, it is possible for the user to supply constants for specific reactions not included in the database, but care must be taken to make sure the formation equation for the newly defined species is written in such a way as to be compatible with the chemical components used by the rest of the program, e.g. if the species A1H2PC>4+ were to be added using the following reaction ... 

The thermodynamic parameters for the formation of several metal-cyanide complexes, among others those of Ni(CN)4 , have been determined using pH-metric and calorimetric methods at 10, 25 and 40°C. In case of nickel(II), the thermodynamic data were determined by titration of Ni(C104)2 solutions with NaCN solutions. The ionic strength of the solutions were 1 < 0.02 M in all cases. The Debye-Huckel equation, related to the SIT model, was used to correct the formation constants to thermodynamic constants valid at 7 = 0. Since previous experiments indicated that the dependence of A,77° in the ionic strength in dilute aqueous solutions is small compared to the experimental error, the measured heats of reaction (A,77 = - 189.1 kJ mol at 10°C A,77 ,= -183.7 kJ mol at 40 C) were taken to be valid at 7 = 0, but the uncertainties were estimated in this review as 2.0 kJ moT. From the values of A,77 , as a function of temperature, average A,C° values were calculated. 

Friedman and Newton have extended their absolute rate calculations of the [Fe(aq)6] reaction to the case of aq = D2O. With the appropriate allowance for differences in solvent libration and Fe—-O stretch frequency, the rate ratio Ah/ d comes out at 1.7, in comparison with the experimental ratio 2.0. Other effects, not calculated in detail, are expected to bridge the gap. " Activation parameters as functions of ionic strength, for outer-sphere reactions between like-charged ions, have been treated using an extended Debye-Huckel theory. The maximum in or observed for certain reactions in the range / = 0 to... 

In dilute solutions it is possible to relate the activity coefficients of ionic species to the composition of the solution, its dielectric properties, the temperature, and certain fundamental constants. Theoretical approaches to the development of such relations trace their origins to classic papers by Debye and Huckel (6-8). For detailed treatments of this subject, refer to standard physical chemistry texts or to treatises on electrolyte solutions [e.g., that by Hamed and Owen (9)]. The Debye-Hiickel theory is useless for quantitative calculations in most of the reaction systems encountered in industrial practice because such systems normally employ concentrated solutions. However, it may be used together with transition state theory to predict the qualitative influence of ionic strength on reaction rate constants. 

Dissociation rates were obtained at high acidity where kn is fast and were corrected for ionic strength using a Debye-Huckel equation. The results show that the cryptate selectivity results mainly from kh and that the transition state for the reaction has little interaction between the metal and the cryptand to differentiate between metals. Rates kt increase with increasing cavity size. The thermodynamics of cryptand formation in water and methanol have also been used to calculate the free energy and enthalpy of transfer of the free ions between the two media. 

---