Standard entropies of hydration

Q Calculate (he value of ihc absolute standard entropy of hydration of the Mg cation. 

Fig. 2.45. Compensation plot of enthalpies vs. standard entropies of hydration fora number of ions. (Reprinted from D. D. Bey and H. G. Evans, Trans. Faraday Soc.34 1093, 1938.)...

Ahyd77°(298K)/kJmor Standard entropy of hydration of M, -140 -no -70 -70 -60... 

Marcus Y (2012) The viscosity B-coeffricient of the thiocyanate anion. J Chem Eng Data Marcus Y, Ben-Naim A (1985) A study of the structure of water and its dependence on solutes, based on the isotope effects on solvation thermodynamics in water. J Chem Phys 83 4744-4759 Marcus Y, Loewenschuss A (1985) Standard entropies of hydration of ions Annu Rep Part C (Royal Soc Chem, London) 1984, 81-135... 

Standard enthalpy of hydration of M " ", AiiydT7 (298K)/kJmoP Standard entropy of hydration ofM " ", AhydS°(298K)/JK moP -2500 -1931 -1586 -1456 -1316 -... 

The calculation of the values for the standard molar entropies of hydration of ions requires some groundwork using the data presented in the following sub-section. 

In this section the standard molar entropies of a small selection of cations and anions are tabulated and the manner of their derivation discussed. The values themselves are required in the calculation of entropies of hydration of ions, discussed in Section 2.7.2. 

The calculation of the standard entropy of the cation depends upon the conventional assumption that the standard entropy of the hydrated proton is zero. A general equation for the standard entropy of an ion M + (aq), including the term for the standard entropy of the hydrated proton(s), may be written as ... 

Absolute Standard Molar Entropies of Hydration of Ions... 

The Absolute Standard Molar Entropy of Hydration of the Proton... 

Table 2.17 Absolute standard molar entropies of hydration for some ions (in J K-1 mol-1)...

The nature of ions in solution is described in some detail and enthalpies and entropies of hydration of many ions are defined and recalculated from the best data available. These values are used to provide an understanding of the periodicities of standard reduction potentials. Standard reduction potential data for all of the elements, group-bygroup, covering the s-and p-, d- and/- blocks of the Periodic Table is also included. Major sections are devoted to the acid/base behaviour and the solubilities of inorganic compounds in water. 

The hydration entropy can also be deduced experimentally (Latimer 18) as the difference between the standard entropy of the hydrated ions (deduced from measurements of the specific heat on the basis of Nernst s Heat Theorem or the Third Law of Thermodynamics) and the theoretically calculated absolute entropy of the gaseous ion, both reckoned per unit volume at constant concentration. This entropy can also be calculated (Eley and Evans18). 

Table 1. Standard enthalpy and entropy of hydration for the protonated species indicated...

The second indicator of kosmotropicity is the standard molar entropy of hydration. For all ions it is highly negative the higher its absolute value, the more water is ordered upon ionic hydration, and the higher the electrolyte kosmotropicity [2,21]. 

Hutchens et al. (1969) determined the heat capacities of zinc insulin at 0 and 0.04 h and of chymotrypsinogen A at 0 and 0.107 h, from 10 to 310 K. For all samples the data were a smooth function of temperature, with no indication of a glass or phase transition at any temperature. The absence of a phase transition corresponding to the ice-liquid water transition is expected for low hydrations. These appear to be the only data in the literature that have been used to determine the entropy of a protein sample. Hutchens et al. (1969) calculated the standard entropy of formation of a peptide bond as 9.0—9.3 cal K mol" . 

The entropy of hydration is the difference between the partial molar entropy of the ion in its standard state in solution and that of the gaseous ion in its standard state. There will be several contributions to this change in entropy, the most significant being ... 

Since AG° = —F , this corresponds to a standard electrode potential of —2..11 V. The hydrated electron is thus an extremely potent reducing agent, much more powerful than the hydrogen atom, for which is —2.10 V. The free energy and heat of hydration are —37.4 and —38.1 Real mole", respectively. The entropy of hydration is —1.90 cal mole" °K" [31]. 

Table 7.3 Conventional Standard Entropies of Ions, and Conventional Entropies jof Hydration at 25 Ct...

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