Heat capacity, standard aqueous species

HEP/HOV] Hepler, L. G., Hovey, J. K., Standard state heat capacities of aqueous electrolytes and some related undissociated species. Can. J. Chem., 74, (1996), 639-646. Cited on page 88. 

Fig. 4. Standard partial molal volumes and isobaric heat capacities of aqueous organic acid species at 25 °C and 1 bar from the critical compilation of Shock (1993a) plotted against the number of moles of carbon in Imol of the species (h). Equations for the correlation curves are given by Shock (1993a)...

References (20, 22, 23, 24, 29, and 74) comprise the series of Technical Notes 270 from the Chemical Thermodynamics Data Center at the National Bureau of Standards. These give selected values of enthalpies and Gibbs energies of formation and of entropies and heat capacities of pure compounds and of aqueous species in their standard states at 25 °C. They include all inorganic compounds of one and two carbon atoms per molecule. 

Table 10.1 Standard Molar Heat Capacities of Species in Dilute Aqueous Solutions at 298.15 K...

Calorimetric measurements yield enthalpy changes directly, and they also yield information on heat capacities, as indicated by equation 10.4-1. Heat capacity calorimeters can be used to determine Cj , directly. It is almost impossible to determine ArCp° from measurements of apparent equilibrium constants of biochemical reactions because the second derivative of In K is required. Data on heat capacities of species in dilute aqueous solutions is quite limited, although the NBS Tables give this information for most of their entries. Goldberg and Tewari (1989) have summarized some of the literature on molar heat capacities of species of biochemical interest in their survey on carbohydrates and their monophosphates. Table 10.1 give some standard molar heat capacities at 298.15 K and their uncertainties. The changes in heat capacities in some chemical reactions are given in Table 10.2. 

As mentioned in Sections 1.1 and 2.9, the third law of thermodynamics makes it possible to obtain the standard Gibbs energy of formation of species in aqueous solution from measurements of the heat capacity of the crystalline reactant down to about 10 K, its solubility in water and heat of solution, the heat of combustion, and the enthalpy of solution. According to the third law, the standard molar entropy of a pure crystalline substance at zero Kelvin is equal to zero. Therefore, the standard molar entropy of the crystalline substance at temperature T is given by... 

This table contains standard state thermodynamic properties of positive and negative ions in aqueous solution. It includes en-thcdpy and Gibbs energy of formation, entropy, and heat capacity, and thus serves as a companion to the preceding table, Standard Thermodynamic Properties of Chemical Substances . The standard state is the hypothetical ideal solution with molality m = 1 mol/kg (mean ionic molality in the case of a species which is assumed to dissociate at infinite dilution). Further details on conventions may be found in Reference 1. 

Harris FE, Rice SA (1954) A chain model for polyelectrolytes. Int J Phys Chem 58 725-732 Heller GT, Marcus Y, Waghorne WE (2002) Enthalpies and entropies of transfer of electrolytes and ions from water to mixed aqueous organic solvents. Chem Rev 102 2773-2836 Helgeson HC, Kirkham DH, Flowers GC (1981) Theoretical prediction of the thermodynamic behavior of aqueous electrolytes at high pressures tmd temperatures IV. Calculation of activity coefficients, osmotic coefficients, and apparent moled and standard and relative partial moM properties to 600 °C and 5 kb. Am J Sci 281 1249-1516 HeplerLG, Hovey JK (1996) Standard state heat capacities ofaqueous electrolytes and some related undissociated species. Can J Chem 74 639-649... 

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