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1.
To quantify the properties of protic ionic liquids (PILs) as acid–base reaction media, potentiometric titrations were carried out in a neat PIL, ethylammonium nitrate (EAN). A linear relationship was found between the 14 pKa values of 12 compounds in EAN and in water. In other words, the pKa value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds. It is possible that this could be explained by the stronger acidity of HNO3 in EAN than that of H3O+ in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from ?1 to 9 on the pH scale based on the pH value in water.  相似文献   

2.
The formation of an appropriate solid electrolyte interphase (SEI) at the anode of a sodium battery is crucially dependent on the electrochemical stability of solvent and electrolyte at the redox potential of Na/Na+ in the respective system. In order to determine entropic contributions to the relative stability of the electrolyte solution, we measure the reaction entropy of Na metal deposition for diglyme (DG) and propylene carbonate (PC) based electrolyte solutions by electrochemical microcalorimetry at single electrodes. We found a large positive reaction entropy for Na+ deposition in DG of ΔR 234 J mol−1 K−1 (c.f.: ΔR 83 J mol−1 K−1), which signals substantial entropic destabilization of Na+ in DG by about 0.73 eV, thus increasing the stability of solvent and electrolyte relative to Na+ reduction. We attribute this strong entropic destabilization to a highly negative solvation entropy of Na+, due to the low dielectric constant and high freezing entropy of DG.  相似文献   

3.
The absolute solvation energies (free energies and enthalpies) of the proton in ammonia are used to compute the pKa of species embedded in ammonia. They are also used to compute the solvation energies of other ions in ammonia. Despite their importance, it is not possible to determine experimentally the solvation energies of the proton in a given solvent. We propose in this work a direct approach to compute the solvation energies of the proton in ammonia from large-sized neutral and protonated ammonia clusters. To undertake this investigation, we performed a geometry optimization of neutral and protonated ammonia 30-mer, 40-mer, and 50 mer to locate stable structures. These structures have been fully optimized at both APFD/6-31++g(d,p) and M06-2X/6-31++g(d,p) levels of theory. An infrared spectroscopic study of these structures has been provided to assess the reliability of our investigation. Using these structures, we have computed the absolute solvation free energy and the absolute solvation enthalpy of the proton in ammonia. It comes out that the absolute solvation free energy of the proton in ammonia is calculated to be −1192 kJ mol–1, whereas the absolute solvation enthalpy is evaluated to be −1214 kJ mol–1. © 2019 Wiley Periodicals, Inc.  相似文献   

4.
The sublimation behavior and thermodynamic properties of the PuIr2 intermetallic compound were determined in this study. Vapor pressures were measured by the Knudsen effusion technique using target collection and mass spectrometry. Sublimation to form elemental Pu(g) predominates for the phases and temperature ranges selected. The enthalpy and entropy of sublimation at 1929 K were 537.1 ± 5.9 kJ mol−1 and 98.4 ± 2.9 J K−1 mol−1 respectively. Third-law analyses using estimated free-energy functions yielded enthalpies of sublimation and formation at 298 K of 547.1 and −195.2 kJ mol−1 respectively. Thermodynamic properties determined in this study were correlated with values obtained from theoretical predictions and from previous studies of analogous intermetallics.  相似文献   

5.
The equilibrium association free enthalpies ΔGa for typical supramolecular complexes in solution are calculated by ab initio quantum chemical methods. Ten neutral and three positively charged complexes with experimental ΔGa values in the range 0 to ?21 kcal mol?1 (on average ?6 kcal mol?1) are investigated. The theoretical approach employs a (nondynamic) single‐structure model, but computes the various energy terms accurately without any special empirical adjustments. Dispersion corrected density functional theory (DFT‐D3) with extended basis sets (triple‐ζ and quadruple‐ζ quality) is used to determine structures and gas‐phase interaction energies (ΔE), the COSMO‐RS continuum solvation model (based on DFT data) provides solvation free enthalpies and the remaining ro‐vibrational enthalpic/entropic contributions are obtained from harmonic frequency calculations. Low‐lying vibrational modes are treated by a free‐rotor approximation. The accurate account of London dispersion interactions is mandatory with contributions in the range ?5 to ?60 kcal mol?1 (up to 200 % of ΔE). Inclusion of three‐body dispersion effects improves the results considerably. A semilocal (TPSS) and a hybrid density functional (PW6B95) have been tested. Although the ΔGa values result as a sum of individually large terms with opposite sign (ΔE vs. solvation and entropy change), the approach provides unprecedented accuracy for ΔGa values with errors of only 2 kcal mol?1 on average. Relative affinities for different guests inside the same host are always obtained correctly. The procedure is suggested as a predictive tool in supramolecular chemistry and can be applied routinely to semirigid systems with 300–400 atoms. The various contributions to binding and enthalpy–entropy compensations are discussed.  相似文献   

6.
In this paper, the kinetics and mechanism of gold nanoparticles formation during the redox reaction between [AuCl4]− complex and l ‐ascorbic acid under different conditions were described. It was also shown that reagent concentration, chloride ions, and pH influence kinetics of nucleation and growth. To establish rate constants of these stages, the model of Finke and Watzky was applied. From Arrhenius and Eyring dependencies, the values of activation energy (22.5 kJ mol−1 for the nucleation step and 30.3 kJ mol−1 for the growth step), entropy (about −228 J K−1 mol−1 for the nucleation step and −128 J K−1 mol−1 for the growth step), and enthalpy (19.8 kJ mol−1 for nucleation and 27.8 kJ mol−1 for particles growth) were determined. It was also shown that the disproporationation reaction had influence on the rate of nanoparticles formation and may have impact on final particles morphology.  相似文献   

7.
The kinetic of D,L-lactide polymerization in presence of biocompatible zirconium acetylacetonate initiator was studied by differential scanning calorimetry in isothermal mode at various temperatures and initiator concentrations. The enthalpy of D,L-lactide polymerization measured directly in DSC cell was found to be ΔH=−17.8±1.4 kJ mol−1. Kinetic curves of D,L-lactide polymerization and propagation rate constants were determined for polymerization with zirconium acetylacetonate at concentrations of 250–1000 ppm and temperature of 160–220 °C. Using model or reversible polymerization the following kinetic and thermodynamic parameters were calculated: activation energy Ea=44.51±5.35 kJ mol−1, preexponential constant lnA=15.47±1.38, entropy of polymerization ΔS=−25.14 J mol−1 K−1. The effect of reaction conditions on the molecular weight of poly(D,L-lactide) was shown.  相似文献   

8.
《Thermochimica Acta》1987,112(2):141-149
Equilibria involving the molecules Ga2S(g), In2S(g), and InGaS(g), by the reaction Ga2S(g) + In2S(g) = 12InGaS(g) were investigated between 1060–1350 K by the Knudsen-effusion, mass-spectrometric method. The reaction enthalpy at 298 K was calculated to be 0±1 kJ mol−1. The enthalpy of formation of InGaS at 298 K and the enthalpy of atomization of InGaS at 298 K were calculated to be 80±18 kJ mol−1 and 710±18 kJ mol−1, respectively. The equilibrium constant and the enthalpy of reaction indicated that the three gaseous molecules have a bent triatomic structure in which S is a center atom and no bond between metals.  相似文献   

9.
10.
The equilibrium constants of the 1:1 NpO2+/benzoate complex were determined by spectrophotometric titrations at variable temperatures (T = 283 to 343 K) and the ionic strength of 1.05 mol · kg−1. The enthalpy of complexation at T = 298 K was determined by microcalorimetric titrations. Similar to other monocarboxylates, benzoate forms a weak complex with NpO2+ and the complexation is strengthened as the temperature is increased. The complexation is endothermic and is entropy-driven. The enhancement of the complexation at elevated temperatures is primarily attributed to the increasingly larger entropy gain when the water molecules are released from the highly-ordered solvation spheres of NpO2+ and benzoate to the bulk solvent where the degree of disorder is higher at higher temperatures. The spectroscopic features of the Np(V)/benzoate system, including the effect of temperature on the absorption bands, are discussed in terms of ligand field splitting and a thermal expansion mechanism.  相似文献   

11.
《Thermochimica Acta》1987,122(2):289-294
The standard enthalpy of formation of potassium metasilicate (K2SiO3), determined by hydrofluoric acid solution calorimetry, was found to be ΔHof,298 = −363.866±0.421 kcal mol−1 (−1522.415±1.762 kj mol−1). The standard enthalpy of formation from the oxides was found to beΔHo298 = −64.786±0.559 kcal mol−1 (−271.065±2.339 kJ mol−1).These experimentally determined data were combined with data from the literature to calculate the Gibbs energies of formation and equilibrium constants of formation over the temperature range of the literature data. The standard enthalpies of formation and Gibbs energies of formation are given as functions of temperature. The standard Gibbs energy of formation is ΔGf,298.150 = −341.705 kcal mol−1 (−1429.694 kJ mol−1).  相似文献   

12.
13.
Intermolecular self-associations of 2,4-pentanediol, 2-methyl-2,4-pentanediol and 1,3-butanediol in carbon tetrachloride solution have been studied by i.r. and 1H-NMR spectroscopy. The spectrophotometric data have been analyzed by the least squares method to obtain the association constants and thermodynamic parameters. It turned out that 2,4-pentanediol, 2-methyl-2,4-pentanediol and 1,3-butanediol all take a cyclic trimer structure through hydrogen bonding. The association constants for trimerization were obtained as 330 and 810 mol−2 dm6 at 30°C, and the enthalpy changes were −34 and −38 kJ mol−1 and entropy changes were −62 and −68 J K−1 mol−1, for 2,4-pentanediol and 2-methyl-2,4-pentanediol, respectively.  相似文献   

14.
《Thermochimica Acta》1986,109(1):63-73
The heat capacity of hydrazinium hydrogen oxalate crystal has been measured between 14 and 300 K. A first-order phase transition was found at 217.6 K. Total transition enthalpy and entropy are 1.09 kJ mol−1 and 4.18 J K−1 mol−1, respectively. The high temperature phase supercooled to 165−170 K. The heat capacity of the supercooled high temperature phase was significantly larger than that of the low temperature phase. By fitting a Schottky heat capacity function to the heat capacity difference, a Schottky energy level was found at (135 ± 4) cm−1 above the ground state and related to the tunneling splitting of the energy levels of the short acidic hydrogen bond. A thermodynamic model of the first-order transition is proposed in which the Schottky anomaly plays the main role. Far-infrared spectra of hydrazinium hydrogen oxalate are reported for the frequency range 400–30 cm−1 at temperatures of 295 and 90 K.  相似文献   

15.
Heat capacities of lanthanum perchlorate octahydrate La(ClO4)38H2O have been measured from 11 to 320 K by an adiabatic calorimeter. Two phase transitions were observed at 115.5 K and 285.2 K, respectively. The enthalpy and entropy of the upper phase transition amounted to 17.97 kJ mol?1 and 62.98 JK?1mol?1. Anomalously large entropy change can be interpreted by a statistical model including a combined positional and orientational disorder of the hydrate water molecules, in accord with an unusually high crystal symmetry of the room temperature phase.  相似文献   

16.
The gas-phase reactions of O . (H2O)n and OH(H2O)n, n=20–38, with nitrogen-containing atmospherically relevant molecules, namely NOx and HNO3, are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and theoretically with the use of DFT calculations. Hydrated O . anions oxidize NO . and NO2 . to NO2 and NO3 through a strongly exothermic reaction with enthalpy of −263±47 kJ mol−1 and −286±42 kJ mol−1, indicating a covalent bond formation. Comparison of the rate coefficients with collision models shows that the reactions are kinetically slow with 3.3 and 6.5 % collision efficiency. Reactions between hydrated OH anions and nitric oxides were not observed in the present experiment and are most likely thermodynamically hindered. In contrast, both hydrated anions are reactive toward HNO3 through proton transfer from nitric acid, yielding hydrated NO3. Although HNO3 is efficiently picked-up by the water clusters, forming (HNO3)0–2(H2O)mNO3 clusters, the overall kinetics of nitrate formation are slow and correspond to an efficiency below 10 %. Combination of the measured reaction thermochemistry with literature values in thermochemical cycles yields ΔHf(O(aq.))=48±42 kJ mol−1 and ΔHf(NO2(aq.))=−125±63 kJ mol−1.  相似文献   

17.
《Tetrahedron》2019,75(48):130693
The efficiency of bicarbonate molecule (HCO3) as a proton shuttle in the tautomerization and (non)enzymatic CO2 hydration reactions has been investigated with the aid of computational chemistry methods (DFT and ab initio). The results revealed that bicarbonate can decrease the barrier height of tautomerization (keto-enol, azo-hydrazo and imine-amine) more than 70%. This value is around 45% for water molecules. Also, HCO3 can catalyze the CO2 hydration both inside (enzymatic) and outside (nonenzymatic) the active site of human carbonic anhydrases II (HCA II). In the absence of enzyme, bicarbonate molecule can lower the CO2 hydration from ∼50 kcal mol−1 in the gas phase to ∼14 kcal mol−1 in the aqueous media. This reaction maintains its barrier (∼15 kcal mol−1) for bicarbonate-Zn complex in the active site of enzyme; it has been observed that amino acid residues, mainly Thr199 and Glu106, are actively involved in the proton transfer network and facilitate CO2 hydration ability of bicarbonate.  相似文献   

18.
《Chemical physics》1986,101(1):17-26
The geometric structures of a number of isomers of the ions formed by protonation of CO2, COS and CS2, and of the parent molecules themselves, have been fully optimized using ab initio quantum chemical methods. Stable minima have been found both for molecules protonated at the terminal atom and at the central carbon atom; ions of the latter type show strong near-degeneracy effects which have been ignored in previous calculations. Proton affinities of CO2, COS and CS2 have been calculated: for CO2 the theoretical result (565 kJ mol−1) is in excellent agreement with experiment (540 kJ mol−1), given that the experimental proton affinity includes a contribution from zero-point vibration of ≈ −27 kJ mol−1. For COS, for which no experimental value is available, the calculations give almost identical results for both O and S protonated species (619 and 636 kJ mol−1, respectively). It may not therefore be possible to distinguish these two isomers experimentally. The theoretical result for CS2 (678 kJ mol) suggests that the current experimental value of the proton affinity (699 kJ mol−1) is too high, since this value includes a zero-point vibration contribution of some −19 kJ mol−1).  相似文献   

19.
Two MOFs of [SrII(5‐NO2‐BDC)(H2O)6] ( 1 ) and [BaII(5‐NO2‐BDC)(H2O)6] ( 2 ) have been synthesized in water using alkaline earth metal salts and the rigid organic ligand 5‐NO2‐H2BDC. The compounds were characterized by elemental analysis, infrared spectrum, thermal analysis, and X‐ray crystallography. Crystal structure analyses have shown that the two complexes are isostructural as evidenced by IR spectra and TG‐DTA. Both compounds present three‐dimensional frameworks built up from infinite chains of edge‐sharing twelve‐membered rings through O–H···O hydrogen bonds. The specific heat capacities of the title complexes have been determined by an improved RD496‐III microcalorimeter with the values of (109.29 ± 0.693) J mol−1 K−1 and (81.162 ± 0.858) J mol−1 K−1 at 298.15 K, and the molar enthalpy changes of the formation reactions of complexes at 298.15 K were calculated as (4.897 ± 0.008) kJ mol−1 and (2.617 ± 0.009) kJ mol−1, respectively.  相似文献   

20.
The ionization enthalpy of benzoic acid has been measured calorimetrically at 25°C in H2ODMSO mixtures ranging from pure water to a maximum DMSO molar ratio XDMSO = 0.80. With the increase of DMSO content, the ionization becomes more and more endothermic, and for XDMSO = 0.8 the ionization enthalpy is about 6 kcal mol?1 higher than in water. By also measuring the solution enthalpy of crystalline benzoic acid in the mixtures, it has been shown that the solvation of the undissociated molecule is the main cause for the increase of the dissociation enthalpy. A comparison has been made between the relative enthalpies of benzoic and hydroxide ions in H2ODMSO mixtures.  相似文献   

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