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1.
The density of tetrapropylammonium bromide aqueous solutions has been measured with six-figure precision at T/K – 273.15 = (5, 10, 15, 20, 25, 30, and 35) and molality from 0.05 to 8 (at 18 closely spaced intervals) using a vibrating-tube densitometer. The apparent molar volume, as well as both the solute and solvent partial molar volumes and their derivatives with respect to temperature, were calculated and compared with those of the tetra-alkyl ammonium (R4N+, R: from methyl to butyl) halide solution series to detect structural transformations due to hydration and hydration interactions.Except for Me4N–Cl, the results indicate progressive solvent structure enhancement in the R4N+ series and significantly different solute–solvent ratios for the “ideal” spatial (“interstitial”) and energetic co-sphere arrangements.  相似文献   

2.
Electrolytic conductivities of some alkali metal halides, MX (M+ = Li+, Na+, and K+; X? = Cl?, Br?, and I?), NaBPh4 and Bu4NBr have been investigated in (20, 40, and 60) mass% {dimethyl sulfoxide (DMSO) in DMSO + acetonitrile} at T = 298.15 K. The conductance results have been analyzed by the Fuoss-conductance-concentration equation in terms of the limiting molar conductance Λ° the association constant KA and the association diameter R. The ionic contributions to the limiting molar conductance have been estimated using Bu4NBPh4 as the “reference electrolyte”. The association constant KA tends to increase in the order mass percent 20 < 40 < 60 DMSO in (DMSO + acetonitrile) which is explained by the thermodynamic parameter ΔG° and Walden product Λ°η. The results have been interpreted in terms of ion–solvent interactions and structural changes in the mixed solvents.  相似文献   

3.
A series of triethylammonium halides (Et3NHCl, Et3NHBr, and Et3NHI) was synthesized. The crystal structures of the three compounds were characterized by X-ray crystallography. The lattice potential energies and ionic radius of the common cation of the three compounds were obtained from crystallographic data. Molar enthalpies of dissolution of the compounds at various values of molality were measured in the double-distilled water at T = 298.150 K by means of an isoperibol solution-reaction calorimeter. According to Pitzer’s theory, the values of molar enthalpies of dissolution at infinite dilution and Pitzer’s parameters of the compounds were obtained. The values of apparent relative molar enthalpies, relative partial molar enthalpies of the solvent and the compounds at different molalities were derived from the experimental values of molar enthalpies of dissolution of the compounds. Finally, hydration enthalpy of the common cation Et3NH+ was calculated to be ΔH+ = ?(150.386 ± 4.071) kJ · mol?1 by designing a thermochemical cycle.  相似文献   

4.
An experimental study on metastable equilibria at T=288 K in the quinary system Li2CO3 + Na2CO3 + K2CO3 + Li2B4O7 + Na2B4O7 + K2B4O7 + H2O was done by isothermal evaporation method. Metastable equilibrium solubilities and densities of the solution were determined experimentally. According to the experimental data, the metastable equilibrium phase diagram under the condition saturated with Li2CO3 was plotted, in which there are four invariant points; nine univariant curves; six fields of crystallization: K2CO3 · 3/2H2O, K2B4O7 · 5H2O, Li2B2O4 · 16H2O, Na2B2O4 · 8H2O, Na2CO3 · 10H2O, NaKCO3 · 6H2O. Some differences were found between the stable phase diagram at T=298 K and the metastable one at T=288 K.  相似文献   

5.
The enthalpies of solution of 1,4-dioxane in {(1  x)F + xH2O}, {(1  x)NMF + xH2O}, and {(1  x)DMF + xH2O} have been measured within the whole mole fraction range at T = 298.15 K. Based on the obtained data, the effect of substituting methyl groups at the nitrogen atom in formamide on the preferential solvation of 1,4-dioxane has been analyzed. A simple model has been proposed to describe the influence of structural and energetic properties of the mixed solvent on the energetic effect of hydrophobic hydration and preferential solvation of 1,4-dioxane by the components of the examined mixture.  相似文献   

6.
7.
Excess molar enthalpies HmEand excess molar volumesVmE of (1,3-dimethyl-2-imidazolidinone  +  benzene, or methylbenzene, or 1,2-dimethylbenzene, or 1,3-dimethylbenzene, or 1,4-dimethylbenzene, or 1,3,5-trimethylbenzene, or ethylbenzene) over the whole range of compositions have been measured at T =  298.15 K. The excess molar enthalpy values were positive for five of the seven systems studied and the excess molar volume values were negative for six of the seven systems studied. The excess enthalpy ranged from a maximum of 435 J · mol  1for (1,3-dimethyl-2-imidazoline  +  1,3,5-trimethylbenzene) to a minimum of   308 J · mol  1for (1,3-dimethyl-2-imidazoline  +  benzene). The excess molar volume values ranged from a maximum of 0.95cm3mol  1 for (1,3-dimethyl-2-imidazoline  +  ethylbenzene) and a minimum of   1.41 cm3mol  1for (1,3-dimethyl-2-imidazoline  +  methylbenzene). The Redlich–Kister polynomial was used to correlate both the excess molar enthalpy and the excess molar volume data and the NRTL and UNIQUAC models were used to correlate the enthalpy of mixing data. The NRTL equation was found to be more suitable than the UNIQUAC equation for these systems. The results are discussed in terms of the polarizability of the aromatic compound and the effect of methyl substituents on the benzene ring.  相似文献   

8.
5–10 μm long, typically 200–300 nm wide, and several nanometers thick LixV2O5  0.8) nanobelts with the δ-type crystal structure were synthesized by a hydrothermal treatment of Li+-exchanged V2O5 gel. When dried at 200 °C under vacuum prior to electrochemical testing, the as-prepared nanobelts underwent the well-known δ  ε  γ-phase transition giving a mixture of ε and γ phases as a nanocomposite electrode material. Such a simple preparation procedure guarantees a yield of material with drastically enhanced initial discharge specific capacity of 490 mAh/g and great cyclability. The enhanced electrochemical performance is attributed to the complex of experimental procedures including post-synthesis treatment of the single-crystalline LixV2O5 nanobelts.  相似文献   

9.
Calorimetric enthalpies of reaction have been measured for the overall biochemical reaction{pyrophosphate(aq)  +  H2O(l)  =  2phosphate (aq)} . The reaction was catalyzed by alkaline phosphatase and, to simplify the thermochemistry, was carried out in the absence of Mg 2 + (aq). Measurements were performed with phosphate buffer ( pH  =  7.19 and 7.94), PIPES buffer ( pH  =  7.13), and HEPES buffer ( pH  =  7.86). The results of these measurements were analyzed by using an equilibrium model. These calculations lead to the standard molar enthalpy changeΔrHmo =   (17.3  ±  0.6)kJ·mol  1 (temperature T =  298.15 K and ionic strengthI =  0) for the reference reaction{HP2O73  (aq)  +  H2O(l)  =  2HPO42  (aq)  +  H + (aq)} . Values of the apparent equilibrium constantK for the overall biochemical reaction from the literature were also analyzed by using the equilibrium model in order to obtain what is believed to be a reliable value for the equilibrium constantK =  4.7 · 10  4 for the reference reaction. The values ofK and ΔrHmo for the reference reaction have been used together with values from the CODATA tables to calculate standard molar formation properties for the pyrophosphate species.  相似文献   

10.
The experimental densities for the binary or ternary systems were determined at T = (298.15, 303.15, and 313.15) K. The ionic liquid methyl trioctylammonium bis(trifluoromethylsulfonyl)imide ([MOA]+[Tf2N]) was used for three of the five binary systems studied. The binary systems were ([MOA]+[Tf2N] + 2-propanol or 1-butanol or 2-butanol) and (1-butanol or 2-butanol + ethyl acetate). The ternary systems were {methyl trioctylammonium bis(trifluoromethylsulfonyl)imide + 2-propanol or 1-butanol or 2-butanol + ethyl acetate}. The binary and ternary excess molar volumes for the above systems were calculated from the experimental density values for each temperature. The Redlich–Kister smoothing polynomial was fitted to the binary excess molar volume data. Virial-Based Mixing Rules were used to correlate the binary excess molar volume data. The binary excess molar volume results showed both negative and positive values over the entire composition range for all the temperatures.The ternary excess molar volume data were successfully correlated with the Cibulka equation using the Redlich–Kister binary parameters.  相似文献   

11.
Lithium-rich Li1.05Mn2O4 hollow nanospheres have been successfully prepared by air-calcining lithiated MnO2 precursor at a low temperature of 550 °C, which was synthesized by chemical lithiation of hollow MnO2 nanospheres with LiI at 70 °C for 12 h. The lithium-rich Li1.05Mn2O4 hollow nanospheres exhibit an excellent cycling stability and rate capability as a cathode material for rechargeable lithium batteries: it maintains 90% of its initial capacity after 500 cycles, and keeps 70% of the reversible capacity at 0.1 C rat, even at 15 C rate.  相似文献   

12.
The excess molar volumes VmE at T=298.15 have been determined in the whole composition domain for (2-methoxyethanol + tetrahydrofuran + cyclohexane) and for the parent binary mixtures. Data on VmE are also reported for (2-ethoxyethanol + cyclohexane). All binaries showed positive VmE values, small for (methoxyethanol + tetrahydrofuran) and large for the other ones. The ternary VmE surface is always positive and exhibits a smooth trend with a maximum corresponding to the binary (2-methoxyethanol + cyclohexane). The capabilities of various models of either predicting or reproducing the ternary data have been compared. The behaviour of VmE and of the excess apparent molar volume of the components is discussed in both binary and ternary mixtures. The results suggest that hydrogen bonding decreases with alcohol dilution and increases with the tetrahydrofuran content in the ternary solutions.  相似文献   

13.
Excess molar volumes VmEof {di- n -butyl ether (DBE)  +  a monofunctional organic compound} have been determined atT =  298.15 K over the whole composition range by means of a vibrating-tube densimeter. TheVmE values were either positive (propylamine, or butylamine, or acetone, or tetrahydrofuran  +  DBE) or negative (methanol, or butanol, or diethyl ether, or cyclopentanone, or acetonitrile  +  DBE). Markedly asymmetric VmEcurves were displayed by (DBE  +  methanol) and (DBE  +  acetonitrile). Partial molar volumes __ Vmoat infinite dilution in DBE, both from this work and the literature, were analysed in terms of an additivity scheme, and the group contributions thus obtained were discussed and compared with analogous results in water. DBE revealed a greater capability of distinguishing between polar and non-polar solutes, as well as in discriminating differently shaped molecules (unbranched, branched, cyclic). The limiting slopes of apparent excess molar volumes are evaluated and briefly discussed in terms of solute–solute and solute–solvent interactions.  相似文献   

14.
Molar calorimetric enthalpy changes ΔrHm(cal) have been measured for the biochemical reactions {cAMP(aq) + H2O(l)=AMP(aq)} and {PEP(aq) + H2O(l)=pyruvate(aq) + phosphate(aq)}. The reactions were catalyzed, respectively, by phosphodiesterase 3,5-cyclic nucleotide and by alkaline phosphatase. The results were analyzed by using a chemical equilibrium model to obtain values of standard molar enthalpies of reaction ΔrHm for the respective reference reactions {cAMP(aq) + H2O(l)=HAMP(aq)} and {PEP3−(aq) + H2O(l)=pyruvate(aq) + HPO2−4(aq)}. Literature values of the apparent equilibrium constants K for the reactions {ATP(aq)=cAMP(aq) + pyrophosphate(aq)}, {ATP(aq) + pyruvate(aq)=ADP(aq) + PEP(aq)}, and {ATP(aq) + pyruvate(aq) + phosphate(aq)=AMP(aq) + PEP(aq) + pyrophosphate(aq)} were also analyzed by using the chemical equilibrium model. These calculations yielded values of the equilibrium constants K and standard molar Gibbs free energy changes ΔrGm for ionic reference reactions that correspond to the overall biochemical reactions. Combination of the standard molar reaction property values (K, ΔrHm, and ΔrGm) with the standard molar formation properties of the AMP, ADP, ATP, pyrophosphate, and pyruvate species led to values of the standard molar enthalpy ΔfHm and Gibbs free energy of formation ΔfGm and the standard partial molar entropy Sm of the cAMP and PEP species. The thermochemical network appears to be reasonably well reinforced and thus lends some confidence to the accuracy of the calculated property values of the variety of species involved in the several reactions considered herein.  相似文献   

15.
A new set of molar heat capacity data for aqueous {2-amino-2-hydroxymethyl-1,3-propanediol (TRIS) + glycol} at (30 to 80) °C and different concentrations (4% to 16% by weight TRIS or 56% to 44% by weight water, in a fixed amount of glycol – 40% by weight) were gathered via reliable measurement method and are presented in this report. The glycols considered were diethylene glycol (DEG), triethylene glycol (TEG), tetraethylene glycol (T4EG), propylene glycol (PG), dipropylene glycol (DPG), and tripropylene glycol (TPG). The 198 data points gathered fit the equation, Cp = Cp,a + B1m + B2m2 + B3m3, where Cp and Cp,a are the molar heat capacities of the (TRIS + glycol + water) and (water + glycol) systems, respectively, Bi the temperature-dependent parameters, and m the mole TRIS per kilogram (glycol + water). The overall average absolute deviation (AAD) of the experimental data from the corresponding values calculated from the correlation equation was 0.07%.  相似文献   

16.
In this study, Nb2O5 nanobelts, with a ca. ∼15 nm in thickness, ca. ∼60 nm in width and several tens of mircrometers in length, have first been used as the electrode material for lithium intercalation over the potential window of 3.0–1.2 V (vs. Li+/Li). It delivers an initial intercalation capacity of 250 mA hg−1 at 0.1 Ag−1 current density, corresponding to x = 2.5 for LxNb2O5, and can still keep relative stable and reaches as large as 180 mA hg−1 after 50 cycles. Surprisingly, the electrodes composed of Nb2O5 nanobelts can work smoothly even at high current density of 10 Ag−1, and shows higher specific capacity and excellent cycling stable, as well as sloped feature in voltage profile. Cycling test indicates Nb2O5 nanobelts electrode shows a high reversible charge/discharge capacity, high rate capability with excellent cycling stability.  相似文献   

17.
Standard values of Gibbs free energy, entropy, and enthalpy of Na2Ti6O13 and Na2Ti3O7 were determined by evaluating emf-measurements of thermodynamically defined solid state electrochemical cells based on a Na–β″-alumina electrolyte. The central part of the anodic half cell consisted of Na2CO3, while two appropriate coexisting phases of the ternary system Na–Ti–O are used as cathodic materials. The cell was placed in an atmosphere containing CO2 and O2. By combining the results of emf-measurements in the temperature range of 573⩽T/K⩽1023 and of adiabatic calorimetric measurements of the heat capacities in the low-temperature region 15⩽T/K⩽300, the thermodynamic data were determined for a wide temperature range of 15⩽T/K⩽1100. The standard molar enthalpy of formation and standard molar entropy at T=298.15 K as determined by emf-measurements are ΔfHm0=(−6277.9±6.5) kJ · mol−1 and Sm0=(404.6±5.3) J · mol−1 · K−1 for Na2Ti6O13 and ΔfHm0=(−3459.2±3.8) kJ · mol−1 and Sm0=(227.8±3.7) J · mol−1 · K−1 for Na2Ti3O7. The standard molar entropy at T=298.15 K obtained from low-temperature calorimetry is Sm0=399.7 J · mol−1 · K−1 and Sm0=229.4 J · mol−1 · K−1 for Na2Ti6O13 and Na2Ti3O7, respectively. The phase widths with respect to Na2O content were studied by using a Na2O-titration technique.  相似文献   

18.
Density and ultrasound speed were measured accurately for diglycine + water, triglycine + water, diglycine + water-polyethylene glycol 400 (PEG400) and triglycine + water-PEG400 solutions at T = (293.15, 298.15, 303.15 and 308.15) K. The results were used in evaluating thermodynamic properties as apparent molar volumes (VØ) and apparent molar isentropic compressions (K) of diglycine and triglycine in water and in PEG400 solutions. Infinite dilution values of these parameters, VoØ, and Ko, were obtained from their plots as a function of molality by extrapolation and have been utilized in obtaining transfer volumes and transfer compressions at infinite dilution. All transfer volumes and transfer compressions were found to increase with increasing molality of PEG400. Apparent molar isobaric expansions were derived from the temperature dependence of VØ values at infinite dilution and at finite concentrations. All the results were interpreted in terms of solute (diglycine or triglycine) and co-solute (PEG400) and solvent (H2O) interactions.  相似文献   

19.
The solubility and the density in the aqueous ternary system (Li2SO4 + MgSO4 + H2O) at T = 308.15 K were determined by the isothermal evaporation. Our experimental results permitted the construction of the phase diagram and the plot of density against composition. It was found that there is one eutectic point for (Li2SO4 · H2O + MgSO4 · 7H2O), two univariant curves, and two crystallization regions corresponding to lithium sulphate monohydrate (Li2SO4 · H2O) and epsomite (MgSO4 · 7H2O). The system belongs to a simple co-saturated type, and neither double salts nor solid solution was found. Based on the Pitzer ion-interaction model and its extended HW models of aqueous electrolyte solution, the solubility of the ternary system at T = 308.15 K has been calculated. The predicted solubility agrees well with the experimental values.  相似文献   

20.
The whole range of solid solutions Li(Li(1−x)/3CoxMn(2−2x)/3)O2 (0  x  1) was firstly synthesized by an aqueous solution method using poly-vinyl alcohol as a synthetic agent to investigate their structure and electrochemical properties. X-ray diffraction results indicated that the synthesized solid solutions showed a single phase without any detectable impurity phase and have a hexagonal structure with some additional peaks caused by monoclinic distortion, especially in the solid solutions with a low Co amount. In the electrochemical examination, the solid solutions in the range between 0.2  x  0.9 showed higher discharge capacity and better cyclability than LiCoO2 (x = 1) on cycling between 2.0 and 4.6 V with 100 mA g−1 at 25 °C. For example, Li(Li0.2Co0.4Mn0.4)O2 (x = 0.4) exhibited a high discharge capacity of 180 mA h g−1 at the 50th cycle. By synthesizing the solid solution between Li2MnO3 and LiCoO2, the electrochemical properties of the end members were improved.  相似文献   

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