Thermodynamic properties of CaTiF5(s)

Calcium titanofluoride CaTiF₅(s) was prepared by solid-state reaction of CaF₂(s) with TiF₃(s) and characterized by X-ray diffraction method. The standard molar isobaric heat capacity $(C_{p\text{,m}}^{\circ })$ of CaTiF₅(s) was determined by a power compensated differential scanning calorimeter in the temperature from 230 K to 710 K. A solid-state galvanic cell with CaF₂ as electrolyte was used to determine the standard molar Gibbs energy of formation $({\mathrm{\Delta }}_{\text{f}}{G}_{\text{m}}^{\circ })$ of CaTiF₅ in the temperature range from 803 K to 1005 K. The galvanic cell can be depicted as:$(-)\text{Pt,}{\text{O}}_2(\text{g,}101.325\text{kPa})/\{\text{CaO(s)}+{\text{CaF}}_2(\text{s})\}//{\text{CaF}}_2//\{{\text{CaTiF}}_5(\text{s})+{\text{CaTiO}}_3(\text{s})\}/{\text{O}}_2(\text{g,}101.325\text{kPa})\text{,Pt}(+)$The second law analysis of present data were carried out to derive the standard entropy $S_{\text{m}}^{\circ }(298.15\text{K})$ and the enthalpy of formation ${\mathrm{\Delta }}_{\text{f}}{H}_{\text{m}}^{\circ }(298.15\text{K})$ and the values derived are 68.7 J · K⁻¹ · mol⁻¹ and −2848.4 kJ · mol⁻¹, respectively.     

A thermodynamic study of ketoreductase-catalyzed reactions 4. Reduction of 2-substituted cyclohexanones in n-hexane

The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone + 2-propanol = cis- and trans-2-substituted cyclohexanol + acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T = 288.15 to 308.05 K. The thermodynamic quantities at T = 298.15 K are: K = (2.13 ± 0.06); ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }=-(1.87\pm 0.06)\text{kJ}·{\text{mol}}^{-1}$; ${\mathrm{\Delta }}_{\text{r}}{H}_{\text{m}}^{\circ }=-(6.56\pm 2.68)\text{kJ}·{\text{mol}}^{-1}$; and ${\mathrm{\Delta }}_{\text{r}}{S}_{\text{m}}^{\circ }=-(15.7\pm 9.2)\text{J}·{\text{K}}^{-1}·{\text{mol}}^{-1}$ for the reaction involving cis-2-methylcyclohexanol, and K = (10.7 ± 0.2); ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }=-(5.87\pm 0.04)\text{kJ}·{\text{mol}}^{-1}$; ${\mathrm{\Delta }}_{\text{r}}{H}_{\text{m}}^{\circ }=-(2.54\pm 1.8)\text{kJ}·{\text{mol}}^{-1}$; and ${\mathrm{\Delta }}_{\text{r}}{S}_{\text{m}}^{\circ }=(11.2\pm 6.4)\text{J}·{\text{K}}^{-1}·{\text{mol}}^{-1}$ for the reaction involving trans-2-methylcyclohexanol. The standard molar Gibbs free energy changes ${\mathrm{\Delta }}_{\text{r}}{G}_{\text{m}}^{\circ }$ for the reactions (trans-2-substituted cyclohexanol = cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereoselective.     

Thermochemistry of 2,2′-dipyridil N-oxide and 2,2′-dipyridil N,N′-dioxide. The dissociation enthalpies of the N−O bonds

In this paper, the first, second and mean (N?O) bond dissociation enthalpies (BDEs) were derived from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the gaseous phase, ${\mathrm{\Delta }}_{\text{f}}{H}_{\text{m}}^{°}(\text{g})$, at T = 298.15 K, of 2,2′-dipyridil N-oxide and 2,2′-dipyridil N,N′-dioxide. These values were calculated from experimental thermodynamic parameters, namely from the standard (p° = 0.1 MPa) molar enthalpies of formation, in the crystalline phase, ${\mathrm{\Delta }}_{\text{f}}{H}_{\text{m}}^{°}(\text{cr})$, at T = 298.15 K, obtained from the standard molar enthalpies of combustion, ${\mathrm{\Delta }}_{\text{c}}{H}_{\text{m}}^{°}$, measured by static bomb combustion calorimetry, and from the standard molar enthalpies of sublimation, at T = 298.15 K, determined from Knudsen mass-loss effusion method.     

Partial molar volumes of organic solutes in water. XX. Glycine(aq) and l-alanine(aq) at temperatures (298 to 443) K and at pressures up to 30 MPa

Density data for dilute aqueous solutions of two amino acids (glycine, l-alanine) obtained using a flow vibrating-tube densimeter are presented together with partial molar volumes at infinite dilution (standard molar volumes, $V_{\text{m,}2}^{°}$) calculated from the measured data. The experiments were performed at temperatures from (298 up to 443) K at pressures close to the saturation line of water, at pressures in the range from (15 to 17) MPa, and at 30 MPa. Values of an analogue of isothermal compressibility, ${\kappa }_{T\text{,}2}^{°}=-(1/V_{\text{m,}2}^{°})(?V_{\text{m,}2}^{°}/?p{)}_T$, are also evaluated. Maxima on the curves $V_{\text{m,}2}^{°}(T)$ and ${\kappa }_{T\text{,}2}^{°}(T)$ are observed and discussed. The new data along with literature values of standard molar volumes and heat capacities are used for generating the recommended parameterization of an equation of state for standard molar thermodynamic properties of the aqueous amino acids.     

Compressibility and volumetric studies of polyethylene-glycols in aqueous,methanolic, and benzene solutions at T = 298.15 K

The speed of sound and density measurements in water, methanol, and benzene solutions for the solutes PEG-400, PEG-1000, and PEG-4000 at T = 298.15 K (0.05 to 0.5 mol · kg⁻¹) are reported. The data obtained are used to calculate thermodynamic parameters such as adiabatic (isentropic) compressibility of solutions (β_ad), apparent molar volume (ϕ_V) and apparent molar compressibility (ϕ_K) for solute molecules in all the solvent media. The limiting partial molar volume $({\varphi }_V^{\circ })$ and limiting partial molar compressibility $({\varphi }_K^{\circ })$ of solute molecules are used to estimate volume of transfer and compressibility of transfer for PEG molecules from methanol to aqueous and benzene to aqueous media. The high observed negative $({\varphi }_K^{\circ })$ values in methanol are interpreted in terms of breakdown of one-dimensional H-bonded structure of methanolic molecules. The (${\varphi }_K^{\circ })$ values observed in water although negative but of small magnitude as compared to salts in water. Attempt is made to estimate hydration number for these molecules in aqueous solutions by applying Shiio’s method and it is observed that PEG-4000 is hydrated most. These results are discussed in terms of solute–solvent and hydrophobic interactions and effects due to conformational characteristic of high molecular weight glycol molecules.