Heat capacities and volumes of some non-electrolytes in N,N-dimethylformamide at 298.15 K

Heat capacities and densities of dilute solutions of formamide, acetone, tetrahydrofuran, ethylene glycol, 2-methoxyethanol, and 2-ethoxyethanol in N,N-dimethylformamide were determined at 298.15 K. Apparent molal heat capacities and volumes for these solutes in DMF were calculated and compared with the analogous data for other substances in DMF solution as well as with the data concerning solutions in methanol and water. Heat capacities of cavity formation (ΔCcav) in DMF were calculated on the basis of the Scaled Particle Theory. ΔCcav appeared to be linearly correlated with the standard partial molal volume of corresponding solutes in DMF. Similar dependences were also found for aqueous and methanolic solutions of the non-electrolytes.

Interactions between cations and sugars. II. Enthalpies, heat capacities, and volumes of aqueous solutions of Ca2+–D-ribose and Ca2+–D-arabinose at 25 °C

The thermodynamic parameters characterizing the interaction between Ca2+ and the suitably positioned sequences of hydroxyls of some sugar isomers have been determined. This was done by comparing the properties of D-ribose which bears such sequences of hydroxyls with the properties of D-arabinose chosen as an inactive reference. The enthalpies of solution and of dilution, the apparent molal heat capacities, and the apparent molal volumes of the two pentoses have been first measured in water at 25 °C. The measurement of these properties for the transfer of the sugars from water to CaCl2 solutions (and, conversely, for the transfer of CaCl2 from water to the sugar solutions) directly gives access to the Ca2+–hydroxyls pair interaction parameters. The thermodynamic properties of this reaction of association may then be estimated: [Formula: see text][Formula: see text] The analysis of these data shows that the weak association constant results from a large compensation between the favourable enthalpy and the unfavourable entropy of reaction.

Apparent molal heat capacities and volumes of aqueous hydrogen sulfide and sodium hydrogen sulfide near 25 °C: the temperature dependence of H2S ionization

A flow microcalorimeter and vibrating tube densimeter were used to obtain apparent molal heat capacities and volumes of aqueous NaHS and Na2S from 0.1 to 1.0 mol kg−1 and of aqueous H2S from 0.03 to 0.08 mol kg−1 at 10, 25, and 40 °C. Standard state heat capacities and volumes for H2S and HS− were obtained by extrapolation to infinite dilution. Combining these results with 25 °C enthalpy data yields an expression for the temperature dependence of the equilibrium constant for H2S neutralization at pressures near those of steam saturation, H2S + OH− = HS− + H2O, log K1b = 19.84 + 930.8/T−2.800 In T, with an estimated uncertainty of ±0.47 at 300 °C. The heat capacity data for bulk aqueous Na2S suggest that the relative concentration of S2− at these molalities is small.

The heat capacities and volumes of some low molecular weight amides, ketones, esters, and ethers in water over the whole solubility range

The densities and heat capacities per unit volume of aqueous solutions of propionamide, methylacetate, ethylacetate, methylethylketone and diethylketone, and bis(2-ethoxyethyl)ether were measured over the whole solubility range with a flow densimeter and a flow microcalorimeter. Most systems were studied at 10, 25, and 40 °C. Properties of the pure liquids were also measured whenever possible. The derived apparent molal volumes [Formula: see text] all decrease with concentration in the water-rich region, except with ethyl acetate which increases at high temperature. In general the more hydrophobic the solute the more negative the initial slope. All apparent molal heat capacities [Formula: see text] decrease as a function of concentration and the decrease is more important for more hydrophobic solutes. The apparent molal expansibilities [Formula: see text] are obtained from [Formula: see text]. They are positive for all solutes but, at low concentrations, they are smaller than the corresponding molar value of the pure liquid. Various factors affecting hydrophobic interactions are examined.

Apparent molal heat capacities and volumes of amino acids in aqueous polyol solutions

Densities (24 °C) and volumetric specific beats (25 °C) were measured for amino acids (0.05–0.5 m) containing apolar side chains in water, and in aqueous solutions of glycerol, mannitol, sorbitol, NaCl, urea, and Gu•HCl, with a flow densimeter and flow microcalorimeter respectively.The derived apparent molal quantifies and transfer functions of the amino acids in aqueous polyol solutions reveal no specificities which might explain the origin of the unique behavior of polyols in protein systems. However, the study did reveal a regular increase in the structure-making ability of the amino acid as the hydrophobicity of the side chains increased. This structure-making tendency was reduced significantly in dilute solutions of the higher polyols.

Apparent molal heat capacities and volumes of aqueous electrolytes at 25 °C: NaClO3, NaClO4, NaNO3, NaBrO3, NaIO3, KClO3, KBrO3, KIO3, NH4NO3, NH4Cl, and NH4ClO4

Measurements at 25 °C with flow calorimeters and densimeters have led to heat capacities and densities of aqueous solutions of 11 1:1 electrolytes: NaClO3, NaBrO3, NaIO3, NaNO3, NaClO4, NH4NO3, KClO3, KBrO3, KIO3, NH4Cl, and NH4ClO4. The first 6 salts were studied up to near saturation. We have used results of these measurements to obtain apparent molal heat capacities and apparent molal volumes of the various solutes. Extrapolation to infinite dilution on the basis of the Debye–Hückel theory bas led to [Formula: see text]and [Formula: see text] values for each solute. We have compared these standard values with results of earlier investigations.

Polyol–Water interactions. Apparent molal heat capacities and volumes of aqueous polyol solutions

Volumetric specific heats (25 °C) and densities (24 °C) were measured with a flow microcalorimeter and flow densimeter for 12 polyols in water (0.05 to 2 m), and for NaCl and n-Bu4NBr in 1 m aqueous alditol solutions. The infinite dilution properties [Formula: see text] of the polyols show specificities in polyol−water interactions which are discussed in terms of the compatibility of the polyol stereochemistry and the existing water environment. The derived heat; capacities and volumes of transfer of hydrophobic and hydrophilic probes to aqueous solutions of homologous polyols suggest that structural interactions are reduced in these systems as compared to pure water.