The thermometric titration of titanium(III) chloride with oxalic acid was carried out at 25°C. The molar ratio of titanium (III): oxalate was found to be 1:2, which indicates the formation of Ti(C2O4)2− ion in acid media. The limiting value of the heat of reaction between Ti(III) ion and oxalic acid in hydrochloric acid solution was found to be −1.5 Kcal mole−1 at 25°C. 相似文献
E. M. F. of the Cell, Cd-Hg (2-phase)/CdAc2(m), Hg2Ac2(s)/Hg was measured at 20°, 25°, 30° and 40°C. The standard e. m. f. of the cell, Cd/CdAc3(m), Hg2Ac2(c)/Hg was evaluated as E°=1.1500?11.09×10?4T+1.06×10?8T2 The thermodynamic data of the reaction, Cd(c) + Hg2Ac2(c)=2Hg(l)+Cd++(aq)+2Ac?(aq) at 25°C were estimated as ΔF°=?42,139, ΔH°=?48,698 cal mole?1 and ΔS°=?22.0 cal deg?1 mole?1 at 25°C. The thermodynamic data for the formation of Hg2Ac2(s) were evaluated as ΔFf°=?202.3, ΔHf°=?154.5 Kcal mole?1 and S°=72.9 cal deg?1 mole?1. From measurements of the heats of solution of CdAc2·2H2O in aqueous solution, the relative partial molal enthalpies of cadmium acetate in aqueous solution were estimated. 相似文献
Nickel(II) chelate of 2–picolylamine has been studied spectrophotometrically in aqueous solution at 25°C and at an ionic strength of 0.3 M. The formation of pink color chelate was pH dependent, and the optimum pH range was between 7.0 to 8.5. Its mole ratio of ligand to nickel(II) ion was found to be 3 to 1 stoichiometry and the formation constant, logK, was determined as 13.31 ± 0.10. By using the wavelength 535 run, determination of trace amount of nickel(II) ion with the sensitivity of 5.28 τ/Cm2 was possible. Enthalpy and entropy changes characterizing the formation of the chelate have been calculated as follows: ΔG°=–8.15Kcal mole-1, ΔH°=–9.65 Kcal mole-1, ΔS°=28.5eu mole-1. 相似文献
The binary system lanthanum-hydrogen has been studied at pressures up to 1 atm at 917°K by a calorimetric-equilibrium method. From the calorimetric measurements we found the enthalpy of formation of LaH2 at 917°K to be ?45.7 kcal mole?1 with an estimated uncertainty at ±0.3 kcal mole?1. This result is about 4 kcal mole?1 less negative than the values derived indirectly from plateau pressure equilibrium measurements by Mulford and Halley and by Korst and Warf. A comparison between the calorimetric and equilibrium measurements at 917°K provides information on the partial entropy of hydrogen in lanthanum and in the dihydride LaH2±δ. The excess entropy of hydrogen in lanthanum is about 6 cal K?1 mole?1 at 917°K: this value is essentially fully accounted for by the estimated vibrational entropy contribution of the hydrogen atoms. In LaH2±δ the partial entropy of hydrogen changes from small negative values at X ≈ 1.95 to positive values for X > 2. This entropy change is explained by an assumed intrinsic disorder of hydrogen in LaH2 of about 0.02. 相似文献
Tetra-n-butyl ammonium bromide (TBAB) semi-clathrate (sc) hydrates of gas are of prime importance in the secondary refrigeration
domain and in the separation of gas molecules by molecular size. However, there is a scarcity of dissociation enthalpies under
pressure of pure gases and gases mixtures for such systems. In addition, the phase equilibrium of TBAB sc hydrates of several
pure gases is not well defined yet as a function of the TBAB concentration and as a function of the pressure. In this paper,
dissociation enthalpies and the phase equilibrium of TBAB sc hydrates of gas have been investigated by differential scanning
calorimetry (DSC) under pressure. Pure gases such as N2 and CO2 and gases mixtures such as N2 + CO2 and CH4 + CO2 were studied. To our knowledge, we present the first phase diagram of TBAB sc hydrates of N2 for different pressures of gas in the TBAB concentration range from 0.170 to 0.350 wt. Enthalpies of dissociation of TBAB
sc hydrates of pure gases and gases mixtures were determined as a function of the presssure for a compound with a congruent
melting point whose hydration number corresponds to 26. 相似文献
The photoconversion of 2′,3′‐dihydro‐6‐nitro‐1′,3′,3′‐trimethylspiro[2H‐1‐benzopyran‐2,2′‐indole] ( Sp ) to its open merocyanine form ( Mc ) in a series of aerated cycloalkanes (cyclopentane, cyclohexane, and trans‐ and cis‐decalin) and of the protonated merocyanine ( McH + ) to Sp in aqueous solution were studied by laser‐induced optoacoustic spectroscopy (LIOAS). The +(11±2) ml mol−1 expansion determined for the ring closure is due to deprotonation of McH + plus the reaction of the ejected proton with the monoanion of malonic acid (added to stabilize Mc ), an intrinsic expansion and a small electrostriction term. The energy difference between Sp and initial McH + is (282±110) kJ mol−1. An intrinsic contraction of −(47±15) ml mol−1 occurs upon ring opening, forming triplet 3Mc in the cycloalkanes, whereas no volume change was detected for the 3Mc to Mc relaxation. Electrostriction decreases the 3Mc energy, (165±18) kJ mol−1, to 135 kJ mol−1. The difference in the values of the ring‐opening ( Sp to Mc ) reaction enthalpy in cycloalkanes as derived from the temperature dependence of the Sp ⇌ Mc equilibrium, (29±8) kJ mol−1, and from the LIOAS data, −(9±25) kJ mol−1, is due to the formation of Mc‐Sp aggregates during steady‐state measurements. The Sp ‐sensitized singlet molecular oxygen, O2(1Δg), quantum yield (average ΦΔ=0.58±0.03) derived from the near‐IR emission of O2(1Δg), was taken as a measure of Mc production in the cycloalkanes. These solvents, albeit troublesome in their handling, provide an additional series for the determination of structural volume changes in nonaqueous media, besides the alkanes already used. 相似文献
We have investigated the low frequency region of h6 and d6 polycrystalline samples of C6H6M(CO)3 by Raman and IR spectroscopies in the 5–300 K temperature range.A complete assignment of low frequency modes is reported. The torsional mode τ′z is observed at 89 cm?1 at 5 K. The intramolecular potential associated with the torsional motion has been found egal to 4.44 and 4.10 kcal.mole?1 at 5 and 120 K respectively. The intermolecular librational potential barrier (16.1 Kcal.mole?1) was deduced from the R′z librational frequency (40 cm?1). The temperature dependance of torsional mode suggests that a large amplitude motion occurs as soon as 150 K. Quasielastic neutron scattering experiments have shown that jumps of C6H6 ring take place and that the corresponding activation energy is equal to 3.9 Kcal.mole?1 (between 260 and 330 K) in agreement with the above potential barrier. The E.I.S.F. seem to favor a 2π/6 jump regime with a correlation time of 4.10?11 s at 300 K. 相似文献
Summary: The range of validity of two popular versions of the nitroxide quasi‐equilibrium (NQE) approximation used in the theory of kinetics of alkoxyamine mediated styrene polymerization, are systematically tested by simulation comparing the approximate and exact solutions of the equations describing the system. The validity of the different versions of the NQE approximation is analyzed in terms of the relative magnitude of (dN/dt)/(dP/dt). The approximation with a rigorous NQE, kc[P][N] = kd[P N], where P, N and P N are living, nitroxide radicals and dormant species respectively, with kinetic constants kc and kd, is found valid only for small values of the equilibrium constant K (10−11–10−12 mol · L−1) and its validity is found to depend strongly of the value of K. On the other hand, the relaxed NQE approximation of Fischer and Fukuda, kc[P][N] = kd[P N]0 was found to be remarkably good up to values of K around 10−8 mol · L−1. This upper bound is numerically found to be 2–3 orders of magnitude smaller than the theoretical one given by Fischer. The relaxed NQE is a better one due to the fact that it never completely neglects dN/dt. It is found that the difference between these approximations lies essentially in the number of significant figures taken for the approximation; still this subtle difference results in dramatic changes in the predicted course of the reaction. Some results confirm previous findings, but a deeper understanding of the physico‐chemical phenomena and their mathematical representation and another viewpoint of the theory is offered. Additionally, experiments and simulations indicate that polymerization rate data alone are not reliable to estimate the value of K, as recently suggested.
Validity of the rigorous nitroxide quasi‐equilibrium assumption as a function of the nitroxide equilibrium constant. 相似文献
The kinetics of the reversible reaction have been studied spectrophotometrically in acid solution under conditions in which both the forward and reverse reactions go to virtual completionand in which the reaction comes to a practical equlibrium. The rates of theforward (Rf) and reverse (Rr) reactions are given by where f, g, h, u, and v have the values (4 ± 1) × 10?5 mole/1.·s, (4.2 ± 0.2) × 10?5 mole2/1.2·s, (5.0 · 0.3) × 10?7 mole3/1.3·s, (1.1 ± 0.1) × 10?3 1.2/mole2·s, and (3.7 ± 0.2) × 10?3 1.3/mole3·s at 298.2°K and at an ionic strength of 2.00M maintained by adding sodium chloride. The stoichiometric equilibrium constant under similar conditions is 0.022 ± 0.003. Differentvalues of these parameters were obtained when sodium perchlorate and sodiumnitrate were used to control ionic strength. The results are compared with those from previous reports and a mechanism is proposed based upon an initial rapid equilibrium followed by a rate-determining attack of water upon H3AsO3I+, H2AsO3I, and HAsO3I?. 相似文献
Small atmospheric ions are always hydrated. The hydration affects their mobility, stability, and lifetime, which are critically important for the determination of nucleation rates. The gas-phase hydration of anions and cations of the atmospheric nucleation precursor H2SO4 has been studied using the Density Functional Theory (DFT). We found that the interaction between the common atmospheric ions and polar water molecules lead to the formation of the strongly hydrogen bonded hydrate complexes, whose thermodynamic stability is much higher than that of neutral atmospheric hydrates (H2SO4)(H2O)n. Both negatively and positively charged hydrates are much more stable than the aforementioned neutral form; however, the hydration of cations is much stronger than that of anions. The difference in hydration free energies is very large (10 kcal mol−1); however, it decreases quickly when the cluster is growing. The observed positive hydration sign preference is consistent with previous studies for pure water. 相似文献
The solid-liquid phase diagrams of binary mixtures of water with tetrabutylammonium carboxylate having an unsaturated alkyl group in the carboxylate anion ((n-C4H9)4NOOCR; R=C2H3–C9H17) were examined in order to confirm the formation of clathrate-like hydrates. The results are summarized as follows: (1) the formation of a clathrate-like hydrate is newly confirmed for all the 13 carboxylates examined; (2) these hydrates are classified into three groups I, II, and III on the basis of the hydration numbers; (3) the group I hydrates, which are formed by the carboxylates with R=C2 and R=C3, have hydration numbers around 30 and are the most stable hydrates among those examined in this study; (4) the group II hydrates, with hydration numbers around 39, are formed by all the carboxylates with R=C4 and C5 including sorbate and are less stable than the group I hydrates; (5) the group III hydrates, with hydration numbers around 30 like the group I hydrates, are formed by carboxylates with long alkyl chains such as 2-octenoate and 2-decenoate and are generally unstable. 相似文献
Closely following the procedure for the preparation of the base‐stabilized dichlorosilylene complex NHCDipp⋅SiCl2 reported by Roesky, Stalke, and co‐workers (Angew. Chem. Int. Ed . 2009 , 48 , 5683–5686), a few crystals of the salt [NHCDipp−H⋅⋅⋅Cl⋅⋅⋅H−NHCDipp]Si(SiCl3)3 were isolated, aside from the reported byproduct [NHCDipp−H+⋅⋅⋅Cl−], and characterized by X‐ray crystallography (NHCDipp=N,N‐di(2,6‐diisopropylphenyl)imidazo‐2‐ylidene). They contain the weakly coordinating anion Si(SiCl3)3−, which was also obtained in high yields upon deprotonation of the conjugate Brønsted acid HSi(SiCl3)3 with NHCDipp or PMP (PMP=1,2,2,6,6‐pentamethylpiperidine). The acidity of HSi(SiCl3)3 was estimated by DFT calculations to be substantially higher than those of other H‐silanes. Further DFT studies on the electronic structure of Si(SiCl3)3−, including the electrostatic potential and the electron localizability, confirmed its low basicity and nucleophilicity compared with other silyl anions. 相似文献