Hydration enthalpy for

Although the data for the silver halides suggest that silver(I) fluoride is likely to be more soluble than the other silver halides (which is in fact the case), the hydration enthalpies for the sodium halides almost exactly balance the lattice energies. What then is the driving force which makes these salts soluble, and which indeed must be responsible for the solution process where this is endothermic We have seen on p. 66 the relationship AG = — TAS and... 

Systems which might be of interest for molecular solvation, and which have been investigated by various techniques are indicated in Table 7. Gas-phase hydration enthalpies for the ions Pb+ X58) and Bi+ 159> are also given in Table 7. In their studies, Tang and Castleman iss.is ) used an apparatus similar to that used by Kebarle and co-workers. Tantalizing as the existence of data for these ions might be for quantum chemists, who would prefer to know more about small ions like Be++, it allows nevertheless the optimistic conclusion that a remarkable increase of activities in the field of gas-phase solvation can be expected in the near future. One should bear in mind that the experimental techniques were introduced only a few years ago. Probably very soon theoreticians will have at their disposal experimented reference data for a lot of interesting systems. 

Table 8. Gas-phase hydration enthalpies for individual clustering steps, and total...

Describe and explain the trend in the ion hydration enthalpies for the halide ions. See Table 8.8. 

The enthalpy of hydration of +2 metal ions is usually in the range of 1600 to 2500 kJ mol-1. Because the sizes of the metal ions decrease in going to the right in the transition series, there will naturally be a general increase in hydration enthalpy in progressing from Ca2+ to Zn2+. Figure 19.8 shows the hydration enthalpies for the +2 ions of the first transition series when plotted in terms of the number of electrons in the d orbitals. 

TABLE 21.9 Comparison of hydration enthalpies for H30" (H20)n i -1- H2O Hj0" "(H20)n reaction calculated using DFT PW91PW91/6-311+- -G(3df,3pd) in Nadykto et al. [43] with available ab initio studies (MP2/cc-pVTZ (MP2), MCCM-UT-CCSD//MP2/cc-pVTZ (MCCM)) [128] and experimental data of Froyd and Lovejoy p25]. The entropies obtained using the DFT are also compared with experimental values (entropies were not reported in the ab initio study [128]). The data are given at ambient temperature of 298.15 K and ambient pressure of 101.3 kPa... 

As expected, the lattice enthalpy for LiF is higher than for CsF. LiF is insoluble, because the hydration enthalpy for Li" (956 kJ mol" ) is insufficient to compensate for the lattice enthalpy of LiF. On the other hand, hydration enthalpy for Cs (710 kJ mol" ) is about the lattice enthalpy for CsF, and it is expected that CsF should be more soluble than LiF. Note that both LiF and CsF contain the same anion, F", and that the hydration of this anion should also be taken into account. However, the hydration enthalpy for F" is insignificant (particularly when compared to the error produced by the Kapustinskii equation) and constant for both compounds, thus it can be ignored for a qualitative analysis like this one. 

In any case, the hydration of Tl is very weak as compared to Tl q (see later discussion), in agreement with the hydration enthalpies for these ions 335 and 4117 kJ mole S respectively (15). This difference is probably an important reason for the slow electron exchange between the two thallium ions because of the necessarily large reorganization energy of their hydration spheres (cf Section IV,B). 

The solubility of the ions in water, on the other hand, is a tradeoff between the hydration enthalpy and the lattice energy. The solubility product, K p, for an ionic compound dissolving in water can be calculated from the sum of the hydration enthalpies for the ions and the reverse of the lattice energy for the ionic solid, as shown in Equations (5.2)-(5.5) ... 

Hydration enthalpies for the first row divalent transition metals as a function of d" electron count. The blue line represents the experimental data, while the red line approximates the experimental values minus the CFSE. [Data are from Shriver and Atkins, Inorganic Chemistry, 4th edition.]... 

The cation-induced shifts in position can be correlated with a number of properties of the exchangeable cations. In addition to the hydration enthalpies, for example, the differences in frequency between the asymmetric and symmetric NO2 stretching bands of 1,3,5-trinitrobenzene are related to the ionic potential of exchangeable cation. Similar cation-induced shifts have been reported in 2002 (82) for DNOC sorbed to smeetite (Fig. 12). The vibrational modes of the symme-... 

Table 15.4 Hydration enthalpies for the sodium, magnesium and aluminium cations... 

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