Alkali metal halide coefficients

Analysis of ion-ion interactions in aqueous salt solutions using the pair potential summarized in eqn (21) in conjunction with theHNC technique (Friedman, 1971) has proved interesting. The value of this approach is indicated by the good agreement between observed and theoretical MacMillan-Mayer osmotic coefficients for lithium chloride in water at 298 K as shown in Fig. 23 (Friedman and Krishnan 1973a). For alkali metal halides in water, Ai3 parameters are... 

Wood et a/.74 have found that the osmotic coefficients for alkali metal halides and nitrates in NMA are much higher than those for the same salts in water. This is attributed to the higher dielectric constant of NMA. Nevertheless the order of the... 

Falcone and Wood179) have reported enthalpies of dilution in NMA for a large series of alkali metal halides as well as for a number of tetraalkylammonium halides (all measurements at 35 °C). These heats were expressed as excess enthalpies180,181) and values of the excess free energies calculated from the previously mentioned osmotic coefficients allowed calculation of the excess entropies. 

Results of analyzing Gibbs energy of transfer data on the basis of equation (4.9.8) for five alkali metal halides and TATB from water to various non-aqueous solvents are summarized in table 4.11. Acceptable fits to equation (4.9.6) are obtained for these systems, the correlation coefficient r decreasing with increase in the size of the alkali metal cation and halide anion. However, there is a problem in assessing the properties of the fit on the basis of the response factors and p. ... 

Limiting Diffusion Coefficients of Alkali Metal Halides in Methanol... 

The disposition of the molten alkali metal halides to the pyrohydrolysis (2.5.13) has been shown in Ref. [258] to decrease together with the increase of radius of both alkali metal cation and halide ion. Apart from the above-said constants, the authors of Ref. [258] estimated the activity coefficients of the solutions of OH- ions in molten alkali metal halides to approach unity (1), i.e. the properties of these solutions are close to ideal ones. Qualitatively the conclusions concerning the activity coefficients agree with the data of Hanf and Sole [255]. Nevertheless, the activity coefficients of hydroxides at the melting points of alkali metal halides are close to unity (1) and then they are reduced by a factor of two or three. 

Bratland et al. reported the investigation of C02 solubility in molten alkali metal halides (NaCl, KC1, KBr, KI) by volumetric, thermogravimetic and freezing methods [270]. The determined dependences of the Henry coefficient against the inverse temperature are described by the following equations ... 

Essential deviations from the theoretical predictions are observed in the saturated solutions of oxides formed by large cations such as PbO, BaO, SrO, which possess appreciable solubilities in alkali-metal halide melts. The experimentally obtained relative thermal coefficient of solubility of lead oxide in the CsCl-KCl-NaCl eutectic melts is approximately three times as high as the theoretical one. This may be explained by the distinction of the electron structure of lead from other studied metals (lead belongs to p-elements) and because of this, lead drops out of all the found regularities. Another possible reason consists in the closeness of the melt temperature (600 or 700 °C) to the melting points of lead oxide (886 °C), and the complete solubility of PbO in all the studied chloride melts is very appreciable [359]. 

Coefficients of the dependences of pEMeO against ) 2 (equation (3.7.16)) for molten alkali-metal halides (confidence level, 0.95)... 

Expressions for the force constant, i.r. absorption frequency, Debye temperature, cohesive energy, and atomization energy of alkali-metal halide crystals have been obtained. Gaussian and modified Gaussian interatomic functions were used as a basis the potential parameters were evaluated, using molecular force constants and interatomic distances. A linear dependence between spectroscopically determined values of crystal ionicity and crystal parameters (e.g. interatomic distances, atomic vibrations) has been observed. Such a correlation permits quantitative prediction of coefficients of thermal expansion and amplitude of thermal vibrations of the atoms. The temperature dependence (295—773 K) of the atomic vibrations for NaF, NaCl, KCl, and KBr has been determined, and molecular dynamics calculations have been performed on Lil and NaCl. Empirical values for free ion polarizabilities of alkali-metal, alkaline-earth-metal, and halide ions have been obtained from static crystal polarizabilities the results for the cations are in agreement with recent experimental and theoretical work. 

Activity coefficients for several alkali metal halides in formamide, derived from freezing point data, have been reported in a series of papers by Vasenko. Other activity coefficient data on the alkali metal halides have been reported by Dawson and Griffith and by Mostkova and co-workers.Gopal and Husain have measured activity coefficients for several tetraalkylammonium and trialkylammonium halides. 

Mean Activity Coefficients of Some Alkali Metal Halides and Potassium Nitrate in Formamide at the Freezing Point... 

Appendix 2.7. lOA summarises these results and includes the for the Li Li electrode which has been calculated from solubiliW data , i.e. the free energy of solution of LiCl is —8.90 kcal mol" in formamide, which leads to a value of AG (LiCl) =1.8 kcal mol" (or 0.0887 V) at 25 C. From eqn. 2.6.35 it is found that for the Li Li electrode in formamide is —2.9748 V at 25°C. The activity coefficients for several of the alkali metal halides are given in Appendix 2.7.12B. 

Qualitative views of ion association have been derived from the trends dealt with above of activity coefficients of series of ions with a common counterion. The trends for at 1 m, being RbCl > Rbl and CsCl > Csl, may be compared with the opposite, increasing trends of the lighter alkali metal halides, MCI < MBr < MI, see Table 7.1. 

The numerical coefficient has been changed from that in [145] to account for the average deviation of the calculated from the experimental values for the alkali metal halides. Cavity formation in molten salts is compatible with their restricted primitive model (RPM), Eq. (3.8) [146]. For a molten salt having N ions of mean diameter d = (r+ + r ) in a volume V, the size distribution of cavities with radii r < 0.5r/ is ... 

It will be noted from Table 13 that single temperature rate coefficients are listed and not Arrhenius parameters. The latter are not readily derived from the original type of experiments, which are not suitable for the measurement of temperature coefficients because of the difficulty of assessing the variations of quantities such as the diffusion coefficient and the limit of detectability of sodium atoms. An interesting competitive method has been developed to study Na and K atom reactions which overcomes these difficulties [146]. The alkali metal atoms were reacted in diffusion flame experiments with pairs of organic halides. By labelling one of the halides with Cl and by analysing for the total concentration and... 

The introduction of competitive alkali metal flame reactions has allowed the experimental determination of activation energy differences for alkali metal flame reactions. The method involves the reaction of sodium or potassium with a pair of organic halides, one of which contains chlorine-36. Analysis of the solid halides produced provides a method of obtaining relative yields of the halides and thus relative rate coefficients. The use of a large temperature range (90—120°C) allows accurate measurements of activation energy differences and ratios of Arrhenius A factors. The values in Table 1 were so obtained. 

RATE COEFFICIENTS AND REACTION MECHANISMS FOR THE REACTIONS OF HALOGENS AND INORGANIC HALIDES WITH ALKALI METAL VAPOURS... 

Nearly all the ions show some temperature dependence in aqueous solution, but at least for the tetraalkylammonium ions, very little in methanol solutions (Figure 4). Instead of increasing, B decreases with increasing size for the alkali metal and halide ions. The negative values of B indicate that most of these ions actually decrease the viscosity upon their addition to water. The B coefficients for the tetraalkylammonium ions increase with increasing size but for the larger ions, B is much larger in aqueous than in methanol solutions and extremely temperature dependent in aqueous solution. 

Scattered data for several other aprotic amides exist. Pistoia and Scrosati have reported the solubilities for several alkali and alkaline earth metal halides and transition metal halides in JV,JV-dimethylacet-amide. The solubilities increase in the order Cl < Br < I. Alexander and co-workers have reported solubility product values for numerous silver salts in DMA. They have also reported values for silver salts, KBr and NaCl in hexamethylphosphorotriamide (HMPT). The solubilities of the silver halides in both these solvents follow the same trend as they do in water. Coleman has measured the solubilities and activity coefficients of sodium and potassium chlorides in several dialkylamides containing water. Distribution coefficients of the salt between water and amide have also been calculated. 

The terms structure making and structure breaking are attributed to Gurney (1953), but Cox and Wolfenden (1934) were the first to mention the notion of water structure in the connection of the viscosities. Furthermore, Frank and Evans (1945) have already used the term structure breaking (but not -making ) with regard to effects of the alkali metal and halide ions, except Li+ and F , on the partial molar entropies of dilute aqueous solutions. The Jones-Dole -coefficient, Eq. (2.35), is the quantitative measure of this effect, and this equation may be recast in the form ... 

The unusual mole fraction scale for the solution, with 5 x(H+,aq) = -68.2 J mol was used for the calculation of values of Astmc5 for the alkali metal and halide ions as well as Ag+ and CIO4 (Abraham et al. 1982). However, the choices of the value of 5 (H+, aq) and the mole fraction scale caused K+ to appear as a strue-ture making ion. This unacceptable result is corrected by adjustment to the molar scale with 5° (H+, aq) = - 22.2 J mol. Linear correlations of Astmc5 with the viscosity coefficients and with the NMR coefficients (Sect. 3.1.3) and also with the ionic partial molar volumes or their electrostricted volumes were noted by Abraham et al. (1982). 

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