Standard Molar Enthalpies Of Solution Research Articles

Equilibria of the ternary systems CsBr–LnBr3 (Ln = Gd, Dy)–H2O and the quaternary system CsBr–GdBr3–HBr (∼12.1 mass %)–H2O at T = 298.15 K and standard molar enthalpies of formation for new compounds

As part of a series of studies, this paper reports experimental phase equilibrium data for CsBr–GdBr3–H2O, CsBr–DyBr3–H2O and CsBr–GdBr3–HBr (∼12.1 mass %)–H2O systems at T = 298.15 K. The phase diagrams were constructed based on the measured data. In the phase diagrams of the ternary system CsBr–GdBr3–H2O and the quaternary system CsBr–GdBr3–HBr (∼12.1 mass %)–H2O,there are all two invariant points, and three crystallization regions corresponding to CsBr, Cs3GdBr6·10H2O, and GdBr3·6H2O, respectively.There are two invariant points and three crystallization regions corresponding to CsBr, Cs3Dy2Br9·16H2O and DyBr3·6H2Oin the system CsBr–DyBr3–H2O.The experimental solubility values of gadolinium bromide and dysprosium bromide at 298.15 K were 65.42 mass % and 65.94 mass %. The compounds Cs3GdBr6·10H2O and Cs3Dy2Br9·16H2O are incongruently soluble in water or a medium of ∼ 12.1 mass % HBr, and were characterized by XRD and TG-DTG techniques. The standard molar enthalpies of solution for Cs3GdBr6·10H2O, Cs3Dy2Br9·16H2O, GdBr3·nH2O (n = 6.00) and DyBr3·nH2O (n = 5.99) were obtainedby means of microcalorimetric measurement, the values found for standard molar enthalpies of formation of Cs3GdBr6·10H2O, Cs3Dy2Br9·16H2O, GdBr3·nH2O (n = 6.00) and DyBr3·nH2O (n = 5.99) were – (5104.8 ± 3.2) kJ·mol−1, – (7827.3 ± 3.6) kJ·mol−1, – (2726.0 ± 2.7) kJ·mol−1 and – (2734.5 ± 3.3) kJ·mol−1, respectively.

Energetics of dehydroepiandrosterone polymorphs I and II from solution and drop-sublimation Calvet microcalorimetry measurements

The lattice enthalpies and monotropic relationship of two dehydroepiandrosterone (DEHA) polymorphs (forms I and II) were evaluated through a combination of differential scanning calorimetry (DSC), isothermal solution microcalorimetry, and drop-sublimation Calvet microcalorimetry experiments. The standard molar enthalpy of transition between both forms was determined as ΔtrsHmo(II→I, 298.15 K) = −0.90 ± 0.07 kJ mol−1 and ΔtrsHmo(II→I, 417.8 K) = −1.7 ± 1.0 kJ mol−1, from measurements of standard molar enthalpies of solution in dimethyl sulfoxide and enthalpies of fusion, respectively. Drop-sublimation Calvet microcalorimetry experiments on form I led to ΔsubHmo(cr I, 298.15 K) = 132.0±3.3 kJ mol−1. This result, when combined with the more precise ΔtrsHmo(II→I) value obtained by solution calorimetry, afforded ΔsubHmo(cr II, 298.15 K) = 131.1±3.3 kJ mol−1. The overall data indicate that on enthalpic grounds form I is more stable than form II from 298.15 K up to fusion. This conclusion, and the fact that DSC experiments indicated that form I has also a considerably higher temperature fusion, namely, Tfus(cr I)= 422.5±0.2 K and Tfus(cr II) = 413.1±0.2 K, suggest that the two polymorphs are monotropically related.

Composition of the Solvation Shell of the Selected Cyclic Ethers (1,4-Dioxane, 12-Crown-4, 15-Crown-5 and 18-Crown-6) in a Mixture of Formamide with Water at Four Temperatures

The solution enthalpy of 15-crown-5 and 18-crown-6 ethers in the mixture of formamide (F) and water (W) was measured at four temperatures: 293.15 K, 298.15 K, 303.15 K, 308.15 K. The standard molar enthalpy of solution, ΔsolHo, depends on the size of cyclic ethers molecules and the temperature. With increasing temperature, the values of ΔsolHo become less negative. The values of the standard partial molar heat capacity Cp,2o of cyclic ethers at 298.15 K have been calculated. The Cp,2o=f(xW) curve shape indicates the hydrophobic hydration process of cyclic ethers in the range of a high-water content in the mixture with formamide. The enthalpic effect of preferential solvation of cyclic ethers was calculated and the effect of temperature on the preferential solvation process was discussed. The process of complex formation between 18C6 molecules and formamide molecules is observed. The cyclic ethers molecules are preferentially solvated by formamide molecules. The mole fraction of formamide in the solvation sphere of cyclic ethers has been calculated.

Solubility Phase Diagrams of ternary systems of CsCl–CdCl2–H2O and CsBr–CdBr2–H2O at T = 298.1 K and the thermodynamic properties of the new solid phase compounds

Using an isothermal equilibrium method, thephaseequilibrium of the ternary systems CsCl–CdCl2–H2O and CsBr–CdBr2–H2O were studied at T = 298.1 K. In thephasediagram of the system CsCl–CdCl2–H2O, the solidphasesof CsCdCl3 and Cs2CdCl4, besides CsCl and CdCl2·2.5H2O, were discovered. Thephasediagramof the system CsBr–CdBr2–H2O contains five crystallization fields for the solidphases CdBr2·4H2O, CsCdBr3, Cs5Cd2Br9, Cs3CdBr5 and CsBr. The new solidphasesof CsCdCl3 and CsCdBr3 are congruently soluble, and Cs2CdCl4, Cs5Cd2Br9 and Cs3CdBr5 are incongruently soluble in the aqueous system. The experimental solubility data and phase diagrams for the ternary systems show more practical application for the obtained cadmium-based halide perovskite. The five new solid phase have been analyzed by X-ray diffraction and thermogravimetry/derivative thermogravimetry. By measuring the standard molar enthalpies of solution of the compounds, the standard molar enthalpies of formation of CsCdCl3, Cs2CdCl4, CsCdBr3, Cs5Cd2Br9, Cs3CdBr5 were determined to be –(873.3 ± 0.7) kJ·mol−1, –(1325.6 ± 0.9) kJ·mol−1, –(742.8 ± 0.7) kJ·mol−1, –(2710.0 ± 1.3) kJ·mol−1 and –(1558.1 ± 1.0) kJ·mol−1, respectively.

Solid–liquid equilibria in the systems cesium bromide + holmium bromide + water and cesium bromide + holmium bromide + hydrobromic acid (~11.7 mass %) + water at T = 298.15 K

The (Solid–Liquid) phase equilibria for the systems of cesium bromide + holmium bromide + water and cesium bromide + holmium bromide + hydrobromic acid (~11.7 mass %) + water at T = 298.15 K were researched by the isothermal dissolution equilibrium method. According to the experimental data, the phase diagrams of the two systems were depicted. There were two invariant points, three invariant curves, and three crystallization fields (CsBr, Cs3Ho2Br9·16H2O, HoBr3·8H2O) in the two phase diagrams. Cs3Ho2Br9·16H2O was incongruently soluble in the two systems. The solubility of HoBr3 measured in water at T = 298.15 K is 65.41 mass %. The compound Cs3Ho2Br9·16H2O was investigated using chemical analysis, XRD and TG-DTG analysis. The standard molar enthalpy of solution of Cs3Ho2Br9·16H2O in water was measured to be −(5.54 ± 0.28) kJ/mol by a microcalorimetry, and its standard molar enthalpy of formation was determined as being –(7846.5 ± 1.2) kJ/mol.

Standard molar enthalpy of the orthorhombic to monoclinic polymorphic phase transition in 4′-hydroxyacetophenone from enthalpy of solution measurements

The standard molar enthalpy of transition between the two known polymorphs of 4′-hydroxyacetophenone (HAP), at 298.15 K, was determined from measurements of their standard molar enthalpies of solution in dimethyl sulfoxide (DMSO). The obtained result ΔtrsHmo(cr II→cr I) = (0.48 ± 0.10) kJ.mol−1 is in excellent agreement with a previously reported value measured in ethanol with an isoperibol calorimeter, using ~ 7 times larger amounts of sample and solvent. The fact that the two polymorphs are easily prepared, and such good agreement was observed between results from two considerably different calorimetric techniques and solvents, suggests that HAP may be a convenient benchmark system for the validation of solution calorimetry measurements or force field predictions on the relative enthalpic stability of organic polymorphs.

Phase equilibria in Mg(NO3)2–Ln(NO3)3 (Ln = Nd, Sm, Eu, Tb)–HNO3 (∼20%)–H2O systems at 298.15 K and thermodynamic properties of Mg3Ln2(NO3)12·24H2O (Ln = Nd, Sm)

The phase diagrams of the Mg(NO3)2–Ln(NO3)3 (Ln = Nd, Sm, Eu, Tb)–HNO3–H2O systems in the (∼20%) HNO3 regions at T = 298.15 K were determined by using an isothermal solution saturation method. The Schreinemaker’s wet residues method was used to determine the compositions of solid-phases. Both Mg(NO3)2–Nd(NO3)3–HNO3–H2O and Mg(NO3)2–Sm(NO3)3–HNO3–H2O systems are complicated with three equilibrium solid phases Mg(NO3)2·6H2O, Mg3Ln2(NO3)12·24H2O and Ln(NO3)3·6H2O (Ln = Nd, Sm). But the systems Mg(NO3)2–Eu(NO3)3–HNO3–H2O and Mg(NO3)2–Tb(NO3)3Tb–HNO3–H2O are simple eutonic type. The two new solid-phase compounds Mg3Nd2(NO3)12·24H2O and Mg3Sm2(NO3)12·24H2O are congruently soluble in an average medium of ∼20 mass % HNO3, and they were identified and characterized by the methods of powder X-ray diffraction, X–ray diffraction single crystal structure analysis, and thermogravimetric/differential thermogravimetric. The XRD diffraction patterns for the two new solid-phase compounds are identical due to their isomorphic structure. They belong to hexagonal systems, with space group R3. For Mg3Nd2(NO3)12·24H2O, a = b = (1.0993 ± 0.0005) nm, c = (1.7211 ± 0.0007) nm, V = (1.8012 ± 0.0013) nm3, Dc = (4.2532 ± 0.0024) g·cm−3, Z = 3; for Mg3Sm2(NO3)12·24H2O, (a = b = 1.1198 ± 0.0004) nm, c = (1.7257 ± 0.0006) nm, V = (1.8742 ± 0.0011) nm3, Dc = (4.1201 ± 0.0012) g cm−3, Z = 3. The standard molar enthalpies of solution of the compounds Mg3Nd2(NO3)12·24H2O and Mg3Sm2(NO3)12·24H2O in water (aq) were measured to be (101.26 ± 0.77) kJ mol−1 and (80.27 ± 0.81) kJ mol−1, and their standard molar enthalpies of formation were calculated to be – (12214.13 ± 2.5) kJ mol−1 and – (12183.6 ± 2.5) kJ mol−1, respectively.

Solid-liquid equilibria for the systems of (CsCl + DyCl3 + H2O) and {CsCl + DyCl3 + HCl (∼10.7%) + H2O} at T = 298.15 K and the thermodynamic properties of the new solid compounds

Solid–liquid equilibria in the ternary system (CsCl + DyCl3 + H2O) and the quaternary system {(CsCl + DyCl3 + HCl (∼10.7%) + H2O} at T = 298.15 K and under 101.3 kPa were investigated by the method of isothermal solution saturation, and the corresponding phase diagrams were constructed. It was found that there were three crystallization regions corresponding to CsCl, Cs2DyCl5·6H2O and DyCl3·6H2O in the ternary system. Nevertheless, four crystallization regions corresponding to CsCl, Cs5DyCl8·6H2O, Cs2DyCl5·6H2O and DyCl3·6H2O were found in the quaternary system. The compound Cs2DyCl5·6H2O was congruently soluble in the two systems, and new double salt Cs5DyCl8·6H2O was formed in the quaternary system which was congruently soluble in an average medium of ∼10.7 mass% HCl. The new solid-phase compounds Cs5DyCl8·6H2O and Cs2DyCl5·6H2O were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of Cs5DyCl8·6H2O and Cs2DyCl5·6H2O in water were measured to be (44.28 ± 0.50) kJ·mol−1 and (5.32 ± 0.27) kJ·mol−1 by microcalorimetry in the condition of infinite dilution, and their standard molar enthalpies of formation were determined to be –(5086.9 ± 1.3) kJ·mol−1 and –(3771.6 ± 0.9) kJ·mol−1. As part of this work, five compounds Cs3LaCl6·3H2O, CsLaCl4·4H2O, CsCeCl4·4H2O, CsPrCl4·6H2O and CsNdCl4·9H2O were synthesized according to the literature [18–21]. The molar enthalpies of solution of Cs3LaCl6·3H2O, CsLaCl4·4H2O, CsCeCl4·4H2O, CsPrCl4·6H2O and CsNdCl4·9H2O in water were also measured to be (14.78 ± 0.31) kJ·mol−1, –(30.98 ± 0.62) kJ·mol−1, –(20.26 ± 0.22) kJ·mol−1, –(19.64 ± 0.54) kJ·mol−1 and –(5.86 ± 0.45) kJ·mol−1 in the condition of infinite dilution, and their standard molar enthalpies of formation were calculated to be –(3351.1 ± 1.1) kJ·mol−1, –(2740.3 ± 1.0) kJ·mol−1, –(2746.1 ± 0.7) kJ·mol−1, –(3326.8 ± 0.9) kJ·mol−1 and –(4189.7 ± 0.9) kJ·mol−1, respectively.

(Solid + Liquid) Phase Equilibria for the Systems CsBr + EuBr3 + H2O and CsBr + EuBr3 + HBr (∼12.3%) + H2O at 298.15 K and Atmospheric Pressure and Thermodynamic and Fluorescent Properties of the New Solid-Phase Compound

In this study, the (solid + liquid) phase equilibria for the two systems of CsBr + EuBr3 + H2O and CsBr + EuBr3 + HBr (∼12.3%) + H2O at 298.15 K and atmospheric pressure were determined by isothermal solubility method. Schreinemaker wet residue approach was used to determin the solid phases obtained from the studied systems. The related phase diagrams were depicted based upon the experimental data. There were two invariant points, three invariant curves, and three crystallization fields corresponding to CsBr, 5CsBr·2EuBr3·20H2O, and EuBr3·6H2O in the two phase diagrams. New double salt 5CsBr·2EuBr3·20H2O was incongruently soluble in the two systems. The content of EuBr3 in two invariant points decreased as the concentration of HBr in equilibrium liquid phase increased, while that of CsBr changed a little. The new solid-phase compound 5CsBr·2EuBr3·20H2O was investigated using chemical, XRD, and TG-DTG analyses. Additionally, the standard molar enthalpy of solution for 5CsBr·2EuBr3·20H2O in water was confir...

Six-membered ring aliphatic compounds: A search for regularities in phase transitions

Absolute vapor pressures of 1-Cl-adamantane, 2-Cl-adamantane, 1-Br-adamantane, 2-Br-adamantane, as well as of Br-cyclohexane were measured by using the transpiration method. Standard molar enthalpies of sublimation of halogen substituted adamantanes at 298.15K were derived from vapor pressure temperature dependences. Standard molar enthalpies of solution of adamantane and halogen adamantanes in cyclohexane were measured with a high-precision solution calorimeter. A theoretical procedure based on the solution calorimetry was applied to derive sublimation enthalpies of halogen adamantanes independently. Molar enthalpies of fusion were measured with help of DSC. The consistent data set of phase transitions for each compound was evaluated and used for discussion of structure-property relations in adamantane and cyclohexane derivatives. A simple way to predict enthalpies of vaporization of compounds containing six-membered rings was suggested for practical thermochemical calculations.

Adamantanes: Benchmarking of thermochemical properties

Standard molar enthalpies of formation of 2-adamantanone and 1-adamantanol were measured by using high-precision combustion calorimetry. Vapour pressures of 2-adamantanone, 1-acetyl-adamantane, 1- and 2-carboxy-adamantanes were measured by using the transpiration method. Standard molar enthalpies of sublimation of this substituted adamantanes at 298.15K were derived from vapour pressure temperature dependences. The standard molar enthalpy of solution of 1-acetyl-adamantane in cyclohexane was measured with the high-precision solution calorimetry. An empirical procedure based on the solution calorimetry was developed to derive sublimation enthalpies of substituted adamantanes independently. Molar enthalpies of fusion of 1-acetyl-adamantane, 1- and 2-carboxy-adamantanes were measured with help of DSC. Thermochemical data on oxygen containing adamantane derivatives were collected and evaluated. Gas-phase enthalpies of formation calculated with the high-level quantum-chemical method G3MP2 and compared with the experimental results. The consistent data set of the benchmark quality is suggested for practical thermochemical calculations.

Phase equilibria of the systems of CsCl + HoCl3 + H2O and CsCl + HoCl3 + HCl (∼10%) + H2O at T = 298.15 K and the thermodynamic and fluorescent properties of the new solid-phase compounds

(Solid+liquid) equilibria in the ternary system CsCl+HoCl3+H2O and in the quaternary system CsCl+HoCl3+HCl (∼10%)+H2O at T=298.15K and atmospheric pressure were investigated by using isothermal solution saturation and moist residue method. Based on the measured solubility data, the corresponding phase diagrams were plotted. In the ternary system, three crystallization regions corresponding to CsCl, Cs2HoCl5·6H2O and HoCl3·6H2O were found. However, there were four crystallization regions corresponding to CsCl, Cs5HoCl8·4H2O, Cs2HoCl5·6H2O and HoCl3·6H2O in the quaternary system. The phase diagrams of the ternary and quaternary systems were compared, and it showed that (1) new solid-phase compound Cs2HoCl5·6H2O was obtained which was congruently soluble in the two systems; (2) a new double salt Cs5HoCl8·4H2O was formed in the quaternary system which was congruently soluble in an average medium of ∼10mass% HCl, and (3) the area of the crystallization region of CsCl decreased with the increasing concentration of HCl in the equilibrium liquid phase. The new solid-phase compounds Cs5HoCl8·4H2O and Cs2HoCl5·6H2O were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of Cs5HoCl8·4H2O and Cs2HoCl5·6H2O in water were confirmed to be (53.09±0.53)kJ·mol−1 and (4.26±0.24)kJ·mol−1 by microcalorimetry in the condition of infinite dilution and their standard molar enthalpies of formation were determined to be −(4530.1±1.4)kJ·mol−1 and −(3776.6±0.9)kJ·mol−1. The fluorescence excitation and emission spectra of the new solid phase compounds were measured. The results indicate that upconversion spectra of the compounds Cs5HoCl8·4H2O and Cs2HoCl5·6H2O at the same wavelength 474nm, when the former was excited at 701nm and the latter was excited at 713nm.

Standard molar Gibbs free energy and enthalpy of solvation of low polar solutes in formamide derivatives at 298 K

Novel experimental values of the limiting activity coefficients and standard molar enthalpies of solution in N-methylformamide at 298.15K are reported and used to calculate the thermodynamic functions of solvation. We compare the plots of the standard molar Gibbs free energy against the standard molar enthalpy of solvation of low polar molecules in N-methylformamide, N,N-dimethylformamide, and formamide. The solvophobic effect is responsible for the deviations of the data points from the straight line corresponding to a correlation between thermodynamic functions of solvation in aprotic solvents. It is shown that the solvophobic effects are strong in formamide solutions, significantly weaker in N-methylformamide, and very weak in N,N-dimethylformamide, which coincides with the average number of intermolecular hydrogen bonds per unit volume of these solvents. Behavior of solutions in binary solvents composed of N-methylformamide or formamide mixed with water and ethylene glycol and a possibility to tune the solvophobic effect by changing the solvent composition are also considered.

(Solid + liquid) equilibria for the ternary system (CsBr + LnBr3 + H2O) (Ln = Pr, Nd, Sm) at T = 298.2 K and atmospheric pressure, thermal and fluorescent properties of Cs2LnBr5·10H2O

The (solid+liquid) phase equilibria of the ternary systems (CsBr+LnBr3+H2O) (Ln=Pr, Nd, Sm) at T=298.2K were studied by the isothermal solubility method. The solid phases formed in the systems were determined by the Schreinemakers wet residues technique, and the corresponding phase diagrams were constructed based on the measured data. Each of the phase diagrams, with two invariant points, three univariant curves, and three crystallization regions corresponding to CsBr, Cs2LnBr5·10H2O and LnBr3·nH2O (n=6, 7), respectively, belongs to the same category. The new solid phase compounds Cs2LnBr5·10H2O are incongruently soluble in water, and they were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of Cs2PrBr5·10H2O, Cs2NdBr5·10H2O and Cs2SmBr5·10H2O in water were measured to be (52.49±0.48)kJ·mol−1, (49.64±0.49)kJ·mol−1 and (50.17±0.48)kJ·mol−1 by microcalorimetry under the condition of infinite dilution, respectively, and their standard molar enthalpies of formation were determined as being −(4739.7±1.4)kJ·mol−1, −(4728.4±1.4)kJ·mol−1 and −(4724.4±1.4)kJ·mol−1, respectively. The fluorescence excitation and emission spectra of Cs2PrBr5·10H2O, Cs2NdBr5·10H2O and Cs2SmBr5·10H2O were measured. The results show that the upconversion spectra of the three new solid phase compounds all exhibit a peak at 524nm when excited at 785nm.

Solid + Liquid Equilibria for the Systems CsBr + ErBr3 + H2O and CsBr + ErBr3 + HBr (∼12.3%) + H2O at 298.15 K and Atmospheric Pressure and Thermodynamic and Fluorescent Properties of the New Solid-Phase Compound

The phase equilibria of the ternary system CsBr + ErBr3 + H2O and the quaternary system CsBr + ErBr3 + HBr (∼12.3 %) + H2O at 298.15 K were determined experimentally with the isothermal solubility method. Based on the measured solubility data, the corresponding phase diagrams were plotted. In the ternary system, three crystallization regions corresponding to CsBr, 3CsBr·2ErBr3·16H2O, and ErBr3·9H2O were found. Similarly, there were three crystallization regions corresponding to CsBr, 3CsBr·2ErBr3·16H2O, and ErBr3·7H2O in the quaternary system. The phase diagrams of the ternary and quaternary systems were compared, and it showed that (1) a new double salt 3CsBr·2ErBr3·16H2O was formed which was incongruently soluble in the two systems; (2) the area of the crystallization region of 3CsBr·2ErBr3·16H2O increased with the increasing concentration of HBr in the equilibrium liquid phase, and (3) ErBr3·9H2O transformed into ErBr3·7H2O when the HBr reached a certain amount. The new solid-phase compound 3CsBr·2ErBr3·16H2O was characterized by chemical analysis, XRD, and TG-DTG techniques. The standard molar enthalpy of solution of 3CsBr·2ErBr3·16H2O in water was confirmed to be −(6.69 ± 0.29) kJ·mol–1 by microcalorimetry in the limit of infinite dilution and its standard molar enthalpy of formation was determined to be −(7846.1 ± 1.2) kJ·mol–1. The fluorescence excitation and emission spectra of 3CsBr·2ErBr3·16H2O were measured. The results indicated that up-conversion spectra of the new solid phase compound exhibit at 470 nm and are excited at 710 nm.

Study on Thermodynamic Properties of Ionic Liquid 1-Ethyl-3-methylimidazolium Alanine

用中和法合成了氨基酸离子液体1-乙基-3-甲基咪唑丙氨酸([C2mim][Ala]),并利用恒温环境的溶解反应热量计,在(288.15±0.01)K-(308.15±0.01)K温度范围内每隔5K,测定不同质量摩尔浓度离子液体在水中的溶解焓(△sol Hm).根据Archer的方法,通过线性拟合得到了该离子液体的标准摩尔溶解焓(△solHmθ),并计算了其相对表观摩尔溶解焓(ΦL).在298.15 K下,根据Glasser经验方法得到了格子能UPOT=566 kJ· mol-1,并计算了其阴阳离子水化焓值(△H++ △H-)=-620 kJ·mol-1及阴离子水化焓△H-([Ala]-)=-387 kJ· mol-1此外,估算了[C2mim][Ala]水溶液的热容(Cp(sol))和表观摩尔热容(ΦCp).

Solid–Liquid Equilibria of the Ternary System CsBr–REBr3–H2O (RE = La, Ce) at 298.15 K, Thermal Properties of Cs2REBr5·10H2O, and Fluorescent Properties of Cs2CeBr5·10H2O

Solubilities were studied for the ternary systems of CsBr–LaBr3–H2O and CsBr–CeBr3–H2O at 298.15 K using the isothermal solubility method; the corresponding phase diagrams were constructed. The solid phases were determined by the Schreinemakers wet residues technique. Three solid phases of CsBr, Cs2LaBr5·10H2O, and LaBr3·7H2O in the system CsBr–LaBr3–H2O, and those of CsBr, Cs2CeBr5·10H2O, and CeBr3·7H2O in the system CsBr–CeBr3–H2O were obtained, respectively. The compounds Cs2LaBr5·10H2O and Cs2CeBr5·10H2O are incongruently soluble in water. The new solid phase compounds Cs2LaBr5·10H2O and Cs2CeBr5·10H2O were characterized by chemical analysis, X-ray diffraction and thermogravimetric/differential thermogravimetric techniques. The standard molar enthalpies of solution of Cs2LaBr5·10H2O and Cs2CeBr5·10H2O in water were measured to be (49.61 ± 0.37) kJ·mol–1 and (50.83 ± 0.46) kJ·mol–1 by microcalorimetry under the condition of infinite dilution, and their standard molar enthalpies of formation were determined as being −(4739.3 ± 1.3) kJ·mol–1 and −(4729.6 ± 1.5) kJ·mol–1. The fluorescence excitation and emission spectra of Cs2CeBr5·10H2O were measured. The results show that upconversion spectra of Cs2CeBr5·10H2O exhibit at 524 nm and 697 nm excited at 785 nm, and the intensity of the emission spectra at 524 nm is stronger than that at 697 nm. This research can provide fundamental data for the rare earth industry and future study. The phase diagrams of the ternary systems could provide the fundamental basis and serve as a guide for the preparation of Cs2LaBr5·10H2O and Cs2CeBr5·10H2O.

Standard partial molar heat capacities and enthalpies of formation of aqueous aluminate under hydrothermal conditions from integral heat of solution measurements

Heats of solution of sodium aluminum oxide, NaAlO2(s), were measured in aqueous sodium hydroxide solutions using a Tian–Calvet heat-flow calorimeter (Setaram, Model C80) with high pressure “batch cells” made of hastelloy C-276, at five temperatures from (373.15 to 523.15)K, steam saturation pressure, and concentrations from (0.02 to 0.09)mol·kg−1. Standard molar enthalpies of solution, ΔsolnH∘, and relative standard molar enthalpies, [H∘(T)−H∘(298.15K)], of NaAl(OH)4(aq) were determined from the measured heats of solution. The results were fitted with the “density” model. The temperature dependence of ΔsolnH∘ from the model yielded the standard molar heat capacities of reaction, ΔsolnCp∘, from which standard partial molar heat capacities for aqueous aluminate, Cp∘[A1(OH)4−,aq], were calculated. Standard partial molar enthalpies of formation, ΔfH∘, and entropies, S∘, of A1(OH)4−(aq) were also determined. The values for Cp∘[A1(OH)4−,aq] agree with literature data determined up to T=413K from enthalpy of solution and heat capacity measurements to within the combined experimental uncertainties. They are consistent with differential heat capacity measurements up to T=573K from Schrödle et al. (2010) [29] using the same calorimeter, but this method has the advantage that measurements could be made at much lower concentrations in the presence of an excess concentration of ligand. To our knowledge, these are the first standard partial molar heat capacities measured under hydrothermal conditions by the integral heat of solution method in a commercial calorimeter to be reported in the literature.

Determination of the Molar Enthalpy of Solution for Ionic Liquid [C5mim][OAc](1-pentyl-3-methylimidazolium acetate) in the Temperature Range from 288.15 to 308.15 K

The molar enthalpies of solution, ΔsolHm, for ionic liquid [C5mim][OAc] with different molalities were measured by the solution-reaction isoperibol calorimeter in the temperature range from 288.15 to 308.15 K with an interval of 5 K. According to Archer’s method, the standard molar enthalpies of solution, ΔsolHmθ, and the apparent relative molar enthalpy, ΦL, for [C5mim][OAc] were determined. In terms of Glasser’s theory of lattice energy, the hydration enthalpy of the cation, ΔH+ ([C5mim]+) = −178 kJ·mol–1 was obtained at 298.15 K. Compared with hydration enthalpy of [C2mim]+, ΔH+ ([C2mim]+) = −233 kJ·mol–1, the hydration of [C5mim]+ is weaker than [C2mim]+. The plot of ΔsolHmθ vs (T – 298.15) K is a good straight line and its slope is the standard molar heat capacity of solution, ΔCp,mθ = 231 J·K–1·mol–1, so that the specific heat capacity of solution, ΔCpθ = 1.09 J·g–1·K–1, was obtained for IL [C5mim][OAc].

Study on the thermodynamic properties for ionic liquid [C6mim][OAc](1-hexyl-3-methylimidazolium acetate)

Using the solution-reaction isoperibol calorimeter, molar enthalpies of solution in water, ΔsolHm, for ionic liquid [C6mim][OAc] with different molalities were measured in the temperature range from (288.15 to 308.15±0.01) K with an interval of 5K. According to Archer's method, the values of the standard molar enthalpies of solution, ΔsolHmθ, were obtained for [C6mim][OAc], respectively. According to Glasser's theory of lattice energy, the hydration enthalpy of cation and anion in infinite dilution aqueous [C6mim][OAc] was calculated, (ΔH++ΔH−)=−598kJmol−1, at 298.15K. The hydration enthalpy of the cation, ΔH+ ([C6mim]+)=−173kJmol−1, was determined. In comparison with hydration enthalpy of [C2mim]+, the hydration enthalpy of [C6mim]+ is a little bit weaker. A linear relationship was found by plotting the experimental values of ΔsolHmθ against (T—298.15) K. The standard molar heat capacity of solution, ΔCp,mθ = 313JK−1mol−1, was obtained from the slope of the regression line, the specific heat capacity of solution, ΔCpθ = 1.38Jg−1K−1, and the apparent relative molar heat capacity, ΦCp, were also calculated for [C6mim][OAc].