Entropy change aqueous solution

When solid AgCl is in contact with its saturated aqueous solution, we have found that, if additional ion pairs are transferred from the surface of the crystal to the solution, the total change of entropy is equivalent to 52.8 e.u Since the entropy of the solid is 23.0 e.u., we find that the partial molal entropy of AgCl in its saturated aqueous solution at 25°C is... 

Solutes in Methanol Solution. In Table 23 we have seen that for four solutes in methanol the viscosity //-coefficients are positive. This is the case even for KC1 and KBr, for which the coefficients are negative in aqueous solution. In Sec. 88 it was pointed out that it would be of interest to see whether this inversion is likewise accompanied by a change in sign for the ionic entropy. Although no accurate values for the entropy of solution of salts in methanol arc available, reliable estimates have been made for KC1, KBr, and NaCl.1 Since the /1-coefficients of KC1 and KBr have been determined both in methanol and in water, all the required data are available for these two solutes. The values of A/S" given in Table 29 have been taken from Table 34 in Chapter 12, where the method of derivation is explained. The cratie term included in each of these values is 14 cal/deg, as already mentioned in Sec. 90. 

The Number of Dipoles per Unit Volume. The Entropy Change Accompanying Proton Transfers. The Equilibrium between a Solid and Its Saturated Solution. Examples of Values of L and AF°. The Change of Solubility with Temperature. Uni-divalent and Other Solutes. Lithium Carbonate in Aqueous Solution. H2COj in Aqueous Solution. Comparison between HjCOj and Li2C03 in Aqueous Solution. Heats of Solution and the Conventional Free Energies and Entropies of Solution. 

The relationship of thermodynamic functions of selective bonding of Hb to a series of carboxylic CP in the variation of the degree of ionization of carboxylic groups is expressed by the effect of enthalpy-entropy compensation (Fig. 18). The compensation effect of enthalpy and entropy components is the most wide-spread characteristic of many reactions in aqueous solutions for systems with a cooperative change in structure [78],... 

A change in the environment of a protein molecule, e.g. adsorption from aqueous solution onto a sorbent surface, may lead to a partial breakdown of its ordered structure, resulting in an increase of conformational entropy. This is a fundamental difference between protein adsorption and the adsorption of flexible polymers, for which attachment to a surface implies a loss of conformational entropy. 

Entropy-related adsorption, known as hydrophobic sorption, involves the partitioning of nonpolar organics from a polar aqueous phase onto hydrophobic surfaces, where they are retained by dispersion forces. The major feature of hydrophobic sorption is the weak interaction between the solute and the solvent. The entropy change is due largely to the destruction of the cavity occupied by the solute in the solvent and the destruction of the structured water shell surrounding the solvated organic. 

Solutions of electrolytes in water do not belong to the group of solutions under discussion, since, in the formation of aqueous solutions of electrolytes, there is a chemical reaction between the ions formed and the water molecules, which changes both the enthalpy and the entropy of the solution. 

Starting from the comparative study of the ionization constants of uracil itself as well as of its several methylated or ethylated derivatives (representing models of tautomeric forms), it may be seen (Table XVII) that uracil and uridine exist in aqueous solution in the diketo form 32. The pX values are not known for the model tautomers 27, 29, and 30, but these forms have been ruled out on the basis of UV studies. Recently the ionization constants of uracil, thymine, their derivatives and nucleotides were determined over the range 10-50°, and thermodynamic enthalpy, entropy, and free energy changes for protonation and depro-tonation of these compounds have been evaluated.93-95,332... 

In these calculations, the electron affinity of the methyl radical has been taken1 as 27 kcal.mole-1. The other enthalpy terms are all well-known quantities the enthalpies of hydration of individual ions have been assigned as done by Valis ev (see ref. 2) and the enthalpy of hydration of the gaseous methyl anion has been taken as that of the bromide ion. It can be seen from Table 1 that not only is the formation of the methyl anion energetically very unfavoured in the gas phase, but it is also endothermic to the extent of 54 kcal.mole-1 in aqueous solution. A check on this final result can be made by consideration of the standard entropy change for the reaction... 

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