Authors:Sonia Jebri, Ali Bechrifa, and Mohamed Jemal
.8 ± 2.1 kJ mol −1 ) [ 18 ], respectively.
A 3 wt% nitric acid solution was used as a solvent for the carbonate phosphoapatites. Measurement of the solution enthalpies was carried out in the 350 cm
at 298.15 K was determined by the Joule effect before the experiment, which were 63.901 ± 0.030 μV mW −1 . The enthalpyofsolution of KCl in deionized water was measured to be 17.581 ± 0.039 kJ mol −1 , which is in good agreement with the value of 17
A direct determination of enthalpy of mixing (ΔHmix) is of interest in predicting miscibility in polymer—polymer systems. Such measurements present, however, working difficulties,
so a reliable indirect approach has been attempted. The enthalpy of mixing ΔHm is obtained by application of Hess law to heat of solution measurement for blends and their components in a common solvent.
For SAN/PMMA blend, corresponding to the weight ratio 50∶50, the experiments were performed by the Hess law approach at 29.4
and 49.3°C on dilute polymer solutions, for various concentrations, getting very good correlation data. This leads to a negative
value of the interaction parameterFHχ(1,2) and by ΔGmix diagram it is possible to make a comparison for each temperature in accordance with the LCST behaviour of these mixtures.
Authors:G. Perlovich, L. Hansen, and A. Bauer-Brandl
Single crystals of the N,N-dimethylformamide (DMF) solvate (1:1) of flurbiprofen (FBP) were grown for the first time and characterised
by X-ray diffraction, IR spectrophotometry, DSC and solution calorimetric methods. The structure may be characterised as a
layer-structure, where DMF double-sheets are arranged between FBP double-sheets. The FBP and DMF molecules are linked to each
other by a hydrogen bond, which is formed between the hydroxyl group of FBP and the carbonyl group of DMF. The conformation
of FBP molecules in the DMF solvate differs from analogous enantiomers in the unsolvated form. The differences are discussed
from the point of view of the influence of the nature of the solvent on selective crystallisation of the enantiomers. A peculiarity
of the solvate is its low melting point, 37.30.2C, with respect to the unsolvated phase, 113.50.2C. Based on solution
enthalpies of the solvated and unsolvated phases dissolved in DMF, the difference in crystal lattice energies, 9.8 kJ mol-1, was calculated and the difference in entropies, 33 J mol-1 K-1 estimated. A possible mechanism explaining the low melting point of the solvate is discussed.
The concentration dependencies of the differential enthalpies of solution along several crystallization paths in the above
mentioned system were measured. On this basis enthalpies of crystallization of equilibrium solid phases occurring there were
A new magnesium borate Mg2[B2O4(OH)2]·H2O has been synthesized by the method of phase transformation of double salt at hydrothermal condition and characterized by XRD, IR, TG and DSC. The enthalpy of solution of Mg2[B2O4(OH)2]·H2O in 0.9764 mol L–1 HCl was determined. With the incorporation of the enthalpies of solution of H3BO3 in HCl (aq), of MgO in (HCl+H3BO3) (aq), and the standard molar enthalpies of formation of MgO(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of –(3185.78±1.91) kJ mol–1 of Mg2[B2O4(OH)2]·H2O was obtained.
2CaO·3B2O3·H2O which has non-linear optical (NLO) property was synthesized under hydrothermal condition and identified by XRD, FTIR and
TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·3B2O3·H2O in HCl·54.572H2O was determined. From a combination of this result with measured enthalpies of solution of H3BO3 in HCl·54.501H2O and of CaO in (HCl+H3BO3) solution, together with the standard molar enthalpies of formation of CaO(s), H3BO3(s), and H2O(l), the standard molar enthalpy of formation of −(5733.7±5.2) kJ mol−1 of 2CaO·3B2O3·H2O was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.
The enthalpies of solution of cyclic ethers: 1,4-dioxane, 12-crown-4 (12C4), and 18-crown-6 (18C6) in water–acetone mixtures
have been measured within the whole mole fraction range at 298.15 K. Based on the obtained data, the effect of base–acid properties
of water–acetone mixtures on the solution enthalpy of cyclic ethers in this mixed solvent has been analyzed. The strong dependence
of the enthalpy of solution (solvation) of cyclic ethers on basic properties of mixed solvent has been observed. The effects
of carbonyl atom replacement in acetone (ACN) molecule by sulfur atom (DMSO molecule) and base–acid properties of mixed solvent
on the solvation process of cyclic ethers have been analyzed.
Authors:H. K. Cammenga, L. O. Figura, and B. Zielasko
The glass transition of isomalt and its components, the enthalpy of solution (crystalline state, glassy state) and the enthalpy of melting are reported. From the measured data (solution enthalpy, enthalpy of fusion and heat capacities) a cycle like the BORN-HABER cycle can be constructed. It is possible to calculate the amounts of amorphous isomalt from measured solution enthalpies; however, the values obtained do not agree with those provided by X-ray powder diffraction studies.