Heat capacity aqueous dissolution

Wood and DeLaney have measured the solubility of He, Ng, Ar, and ethane in pure A-methylacetamide from 35 to 70°C and used the data to calculate the free energy, heat and entropy of solution, as well as the change in heat capacity for the dissolution process. (See Appendix 2.3.2.) Non-polar solutes appear to be much more soluble in iV-methyl-acetamide than in water. Entropies of solution are not as negative as for aqueous solutions, but the change in heat capacity on dissolution is much more negative than in water. These results lead to some interesting conclusions as to the structural effects of non-polar solutes on this solvent. 

The heat capacity change upon aqueous dissolution of nonpolar molecules from the gaseous phase and from the liquid phase is positive and is proportional to the surface area of the solute molecule (Edsall, 1935 Gill and Wadso, 1976). 

Due to the kinetically inert nature of nickel oxide with respect to its dissolution in aqueous media the solubility of NiO has been studied only at elevated temperatures so far [80TRE/LEB2], [89ZIE/JON]. These studies are not suitable for the calculation of any thermodynamic properties of NiO because of the high uncertainty of the measured solubilities compared to the high-temperature emf data and the low-temperature heat capac-... 

No heat capacity data have been reported for electrolytes in ethanol. However, from the temperature coefficients of the heats of dissolution of Nal in ethanol, an average AC for the dissolution process may be estimated at 16 cal mol K". For aqueous solutions of simple electrolytes AC is generally negative. ... 

The solubilities of the scale-forming salts barium and strontium sulphates in aqueous solutions of sodium chloride have been reviewed by Raju and Atkinson (1988, 1989). Equations were proposed for the prediction of specific heat capacity, enthalpy and entropy of dissolution, etc., for all the species in the solubility equilibrium, and the major thermodynamic quantities and equilibrium constraints expressed as a function of temperature. Activity coefficients were calculated for given temperatures and NaCl concentrations and a computer program was used to predict the solubility of BaS04 up to 300 °C and SrS04 up to 125 °C. 

Ions in aqueous solutions are characterized by several thermodynamic quantities in addition to the molar volumes, heat capacities and entropies discussed above. These are the molar changes of enthalpy, entropy, and Gibbs energy on the transfer of an ion from its isolated state in the ideal gas to the aqueous solution. They pertain also to the dissolution of an electrolyte in water, since they can be considered as parts in a thermodynamic cycle in which the electrolyte is transferred to the gas phase, dissociates there into its constituent ions, which are then transferred into the solution. Contrary to thought processes, as described in Sect. 2.2., it is impossible to deal experimentally with individual ions but only with entire electrolytes or with such combinations (sums or differences) of ions that are neutral. The assignment of values to individual ions requires the splitting of the electrolyte values by some extra-thermodynamic assumption that cannot be proved or disproved within the framework of thermodynamics. However, for a theoretical estimation of the individual ionic... 

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