首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Low-temperature calorimetric measurements have been performed on DyBr3(s) in the temperature range (5.5 to 420 K ) and on DyI3(s) from T=4 K to T=420 K. The data reveal enhanced heat capacities below T=10 K, consisting of a magnetic and an electronic contribution. From the experimental data on DyBr3(s) a C0p,m (298.15 K) of (102.2±0.2) J·K−1·mol−1 and a value for {S0m (298.15 K)  S0m (5.5 K)} of (205.5±0.5) J·K−1·mol−1, have been obtained. For DyI3(s), {S0m (298.15 K)  S0m (4 K)} and C0p,m (298.15 K) have been determined as (226.9±0.5) J·K−1·mol−1 and (103.4±0.2) J·K−1·mol−1, respectively. The values for {S0m (5.5 K)  S0m (0)} for DyBr3(s) and {S0m (4 K)  S0m (0)} for DyI3(s) have been calculated, giving S0m (298.15 K)=(212.3±0.9) J·K−1·mol−1 in case of DyBr3(s) and S0m (298.15 K) =(233.1±0.7) J·K−1·mol−1 for DyI3(s). The high-temperature enthalpy increment has been measured for DyBr3(s) in the temperature range (525 to 799 K) and for DyI3(s) in the temperature range (525 to 627 K). From the results obtained and enthalpies of formation from the literature, thermodynamic functions for DyBr3(s) and DyI3(s) have been calculated from T→0 to their melting temperatures at 1151.0 K and 1251.5 K, respectively.  相似文献   

2.
In this Letter we report the results of the measurements of the rate coefficients for thermal attachment to several perfluoroethers namely perfluorodiglyme (C6F14O3), perfluorotriglyme (C8F18O4), perfluoropolyether (CF3–(OCF(CF3)CF2)n–(OCF2)m–OCF3) and perfluorocrownether ((C2F4O)5). Rate coefficients were obtained under thermal conditions in the temperature range 298–378 K. The increase of the rates with temperature follows the Arrhenius law and the activation energies have been obtained from the slope of the ln(k) vs. 1/T. The respective values of the rate coefficients (at 298 K) and activation energies are as follows: 7.7 ± 1.2 × 10?11 cm3 s?1 (0.18 ± 0.005 eV), 6.7 ± 2.1 × 10?11 cm3 s?1 (0.25 ± 0.004 eV), 2.1 ± 0.2 × 10?10 cm3 s?1 (0.16 ± 0.010 eV), 3.1 × 10?11 cm3 s?1 (0.27 ± 0.003 eV) for C6F14O3, C8F18O4, CF3–(OCF(CF3)CF2)n–(OCF2)m–OCF3 and (C2F4O)5.  相似文献   

3.
A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (λmax of [Fe(CN)5PhNHNH2]3?, complex) under the optimum reaction conditions at: 2.5 × 10?3 M [Fe(CN)6]4?, 1.0 × 10?3 M [PhNHNH2], 8.0 × 10?7 M [Ag+], pH 2.8 ± 0.02, ionic strength (μ) 0.02 M (KNO3) and temperature 30 ± 0.1 °C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8–8.0 × 10?8 M with a detection limit of 2 × 10?9 M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst–inhibitor (KCI), catalyst–substrate (Ks) and Michaelis–Menten constant (Km) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.  相似文献   

4.
Heat capacities of 2,2-dimethyl-1,3-propanediol(CH3)2C(CH2OH)2 were measured in the temperature range between T =  13 K and T =  350 K using an adiabatic calorimeter. The compound underwent a first-order phase transition at T =  (314.5  ±  0.1) K. The enthalpy and the entropy of transition were (12.52  ±  0.02)kJ · mol  1and (39.81  ±  0.08)J · K  1· mol  1, respectively. Measurement of the fusion peak by d.s.c. showed that the purity of the sample was 0.9999 mass fraction and the entropy of fusion was 9.9 J · K  1· mol  1. Another first-order phase transition was observed at T =  (60.4  ±  0.1) K with the associated entropy change of (2.93  ±  0.05)J · K  1· mol  1. Heat capacities of two deuterated samples,(CH3)2C(CH2OD)2 and(CD3)2C(CD2OD)2 , were also measured and the results were compared with those on the natural compound. Possible mechanisms of the transition have been discussed from the isotope effects on the thermodynamic quantities associated with the transition. Standard thermodynamic functions of the compounds are tabulated.  相似文献   

5.
The thermodynamic parameters, ΔBG, ΔBH, ΔBS, and ΔBCp, of the drugs flurbiprofen (FLP), nabumetone (NAB), and naproxen (NPX) binding to β-cyclodextrin (βCD) and to γ-cyclodextrin (γCD) in 0.10 M sodium phosphate buffer were determined from isothermal titration calorimetry (ITC) measurements over the temperature range from 293.15 K to 313.15 K. The heat capacity changes for the binding reactions ranged from −(362 ± 48) J · mol−1 · K−1 for FLP and −(238 ± 90) J · mol−1 · K−1 for NAB binding in the βCD cavity to 0 for FLP and −(25.1 ± 9.2) J · mol−1 · K−1 for NPX binding in the larger γCD cavity, implying that the structure of water is reorganized in the βCD binding reactions but not reorganized in the γCD binding reactions. Comparison of the fluorescence enhancements of FLP and NAB upon transferring from the aqueous buffer to isopropanol with the maximum fluorescence enhancements observed for their βCD binding reactions indicated that some localized water was retained in the FLP–βCD complex and almost none in the NAB–βCD complex. No fluorescence change occurs with drug binding in the larger γCD cavity, indicating the retention of the bulk water environment in the drug–γCD complex. Since the specific drug binding interactions are essentially the same for βCD and γCD, these differences in the retention of bulk water may account for the enthalpically driven nature of the βCD binding reactions and the entropically driven nature of the γCD binding reactions.  相似文献   

6.
Low-temperature heat capacities of pyrimethanil laurate (C24H37N3O2) were precisely measured with an automated adiabatic calorimeter over the temperature range between T = 78 K and T = 340 K. The sample was observed to melt at (321.52 ± 0.04) K. The molar enthalpy and entropy of fusion as well as the chemical purity of the compound were determined to be (67244 ± 11) J · mol−1, (209.28 ± 0.02) J · mol−1 · K−1, (0.9943 ± 0.0004) mass fraction, respectively. The extrapolated melting temperature for the absolutely pure compound obtained from fractional melting experiments was (322.264 ± 0.006) K.  相似文献   

7.
8.
Electron paramagnetic resonance (EPR) study of Cu2+ doped bis (glycinato) Mg (II) monohydrate single crystals is carried out at room temperature. Copper enters the lattice substitutionally and is trapped at two magnetically inequivalent sites. The observed spectra are fitted to a spin-Hamiltonian of rhombic symmetry with the following values of the parameters: Cu2+ (I), gx = 2.1577 ± 0.0002, gy = 2.2018 ± 0.0002, gz = 2.3259 ± 0.0002, Ax = (87 ± 2) × 10?4 cm?1, Ay = (107 ± 2) × 10?4 cm?1, Az = (141 ± 2) × 10?4 cm?1; Cu 2+ (II), gx = 2.1108 ± 0.0002, gy = 2.1622 ± 0.0002, gz = 2.2971 ± 0.0002, Ax = (69 ± 2) × 10?4 cm?1, Ay = (117 ± 2) × 10?4 cm?1and Az = (134 ± 2) × 10?4 cm?1. The ground state wave function of the Cu2+ ion in this lattice is evaluated to be predominantly |x2 ? y2. The g-factor anisotropy is also calculated and compared with the experimental value. With the help of the optical absorption study, the nature of bonding in the complex is discussed.  相似文献   

9.
Some heterogeneous reactions of oxide ion exchange (carbonate ion dissociation and magnesium oxide dissolution) in the molten {KCl + LiCl} eutectic at temperatures of (873, 973 and 1073) K were studied using an electrochemical cell with an oxygen membrane electrode Pt(O2)|ZrO2(Y2O3). The dissociation constant of the CO32− was found to increase with increasing temperature: pK (873 K)=(2.39 ± 0.05); pK (973 K)=(1.81 ± 0.09); pK (1073 K)=(1.53 ± 0.08). Removal of CO2 from the gas above the melt allows the complete transformation of CO32− to O2−. pPMgO values decrease more from (6.99 ± 0.08) to (5.41 ± 0.04). The oxobasicity indices, pI(KCl+LiCl), were calculated from the solubility data to be 3.2 at 873 K, 3.4 at 973 K, and 3.6 at 1073 K. This trend suggests an increase in acidity with increasing temperature of {KCl + LiCl}.  相似文献   

10.
N. Xaba  D. Jaganyi 《Polyhedron》2009,28(6):1145-1149
Hydroboration reactions of 4-octene with HBBr2 · SMe2, HBCl2 · SMe2 and H2BBr · SMe2 in CH2Cl2 were studied as function of concentration and temperature and compared with those of 1-octene. On average, hydroboration with dihaloborane proceeded 16 times slower for 4-octene than for 1-octene. In the case of the reactions with the monohaloborane, this factor is halved. This can be explained by the difference in the relative rates of dissociates of Me2S from the dihaloborane and a monohaloborane complex, respectively. The reactions involving H2BBr · SMe2 also exhibited a k?2 value, an indication of the presence of a parallel reaction, most likely a rearrangement process facilitating isomerization by way of a π-complex. The moderate ΔH values accompanied by small ΔS values (94 ± 4 kJ mol?1, ?3 ± 13 J K?1 mol?1 for HBBr2 · SMe2; 93 ± 1 kJ mol?1, ?17 ± 4 J K?1 mol?1 for HBCl2 · SMe2 and in the case of H2BBr · SMe2, 90 ± 13 kJ mol?1, +12 ± 44 J K?1 mol?1 and 83 ± 13 kJ mol?1, ?24 ± 45 J K?1 mol?1, respectively, for the k2 and k?2 processes) imply a process that is dissociatively dominated, with the overall mode of activation being interchange dissociative (Id).  相似文献   

11.
Thermodynamic properties of Mg(NH2)2 and LiNH2 were investigated by measurements of NH3 pressure-composition isotherms (PCI). Van’t Hoff plot of plateau pressures of PCI for decomposition of Mg(NH2)2 indicated the standard enthalpy and entropy change of the reactions were ΔH° = (120 ± 11) kJ · mol?1 (per unit amount of NH3) and ΔS° = (182 ± 19) J · mol?1 · K?1 for the reaction: Mg(NH2)2  MgNH + NH3, and ΔH° = 112 kJ · mol?1 and ΔSo = 157 J · mol?1 · K?1 for the reaction: MgNH  (1/3)Mg3N2 + (1/3)NH3. PCI measurements for formation of LiNH2 were carried out, and temperature dependence of plateau pressures indicated ΔH° = (?108 ± 15) kJ · mol?1 and ΔS° = (?143 ± 25) J · mol?1 · K?1 for the reaction: Li2NH + NH3  2LiNH2.  相似文献   

12.
The molar enthalpies of reaction of metallic barium with 0.047 mol·dm−3 HClO4 as well as the molar enthalpies of dissolution of BaCl2 in 1.01 mol·dm−3 HCl and in water have been measured at T=298.15 K in a sealed swinging calorimeter with an isothermal jacket. From these results the standard molar enthalpy of formation of the barium ion in an aqueous solution at infinite dilution, as well as the enthalpies of formation of barium chloride and barium perchlorate, are calculated to be: ΔfH0m(Ba2+,aq)=−(535.83±1.25) kJ · mol−1; ΔfH0m(BaCl2,cr)=−(855.66±1.28) kJ · mol−1; and ΔfH0m(BaClO4,cr)=−(796.26±1.35) kJ · mol−1. The results obtained are discussed and compared with previous experimental values.  相似文献   

13.
The fluoride affinities of fluorinated alanes, AlHmF3?m (m = 1–3) were measured using energy-resolved collision-induced dissociation of fluorinated aluminate anions. The AlHmF4?m? anions were formed by reaction of dimethylethylamine-alane with fluoride ion and F2. From the measured bond dissociation energies, the fluoride affinities of fluorinated alanes are determined to be 93.2 ± 3.1, 97.5 ± 4.0, and 108.6 ± 3.7 kcal/mol for m = 3, 2, and 1, respectively. The fluoride affinities are in good agreement with the theoretical calculations at the CCSD(T)/CBS and B3LYP/6-31 + G* levels of theory. The increased Lewis acidity of more fluorinated alanes is attributed to increased positive charge density on the aluminum.  相似文献   

14.
Low-temperature heat capacities of the 9-fluorenemethanol (C14H12O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T=78 K and T=390 K. The solid–liquid phase transition of the compound has been observed to be Tfus=(376.567±0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be ΔfusHm=(26.273±0.013) kJ · mol−1 and ΔfusSm=(69.770±0.035) J · K−1 · mol−1. The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, ΔcU(C14H12O, s)=−(7125.56 ± 4.62) kJ · mol−1 and ΔcHm(C14H12O, s)=−(7131.76 ± 4.62) kJ · mol−1, by means of a homemade precision oxygen-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of formation of the compound has been derived, ΔfHm(C14H12O,s)=−(92.36 ± 0.97) kJ · mol−1, from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.  相似文献   

15.
Nanoparticles of α-Bi2Mo3O12 were prepared by co-precipitation method at calcination temperatures of 250, 300, 400 and 480 °C. The characterization of α-Bi2Mo3O12 synthesized at different temperatures was carried out by X-ray diffraction (XRD), thermal analysis (TGA/DTA), transmission electron microscopy (TEM), and diffuse reflectance spectroscopy (DRS). Adsorption parameters and photocatalytical activity under visible light irradiation of α-Bi2Mo3O12 were evaluated using the rhodamine B (rhB) dye as model. The adsorption constant (K) and maximum amount of dye adsorbed (qmax) on the surface of the samples synthesized were evaluated following the Langmuir isotherm. The sample calcinated at 250 °C showed the maximum adsorption percentage of dye, which ranged between 20 and 46% for initial concentrations of rhB from 5 to 15 mg L?1, with a K = 6.96 × 105 L mol?1 and qmax = 2.73 mg g?1. All samples were able to induce the oxidative photodegradation of rhB, however, the bleaching of dye solution was reached more quickly for the sample calcinated at 250 °C.  相似文献   

16.
《Polyhedron》2005,24(16-17):2102-2107
Four complexes of M(NO3)2(4NOPy-OMe)2, (4NOPy-OMe = 4-(N-tert-butyloxylamino)-2-(methoxymethylenyl)pyridine, and M = MnII, 1; CoII, 2; NiII, 3; CuII, 4), were prepared and fully characterized. X-ray single crystal analysis reveals that four complexes are isostructural. The molecular structures are distorted octahedral in which the methoxy oxygen atoms coordinate to the metal ion by trans-configuration while the pyridyl nitrogen atoms and the nitrate oxygen atoms coordinate by cis-configuration. The magnetic properties of all complexes were investigated by SQUID magneto/susceptometry. Temperature dependence of the molar magnetic susceptibilities in the temperature range of 2–300 K indicated that the magnetic coupling between aminoxyl radicals and metal ion was antiferromagnetic in the complex 1 and were ferromagnetic in the complexes 24. The quantitative analysis based on the spin Hamiltonian, H = −2J(S1SM + SMS2) yielded the best fit as J/kB = −13.4 ± 0.1 K, g = 1.94 ± 0.002, and θ = −0.78 ± 0.02 K for the complex 1, J/kB = 48.7 ± 2.1 K, g = 2.07 ± 0.02, and θ = −2.83 ± 0.41 K for the complex 3 (the data in the temperature range 300–50 K were used), and J/kB = 57.0 ± 1.2 K, g = 2.002 ± 0.004, and θ = −9.8 ± 0.1 K for the complex 4.  相似文献   

17.
The thermodynamic properties ofZn5(OH)6(CO3)2 , hydrozincite, have been determined by performing solubility and d.s.c. measurements. The solubility constant in aqueous NaClO4media has been measured at temperatures ranging from 288.15 K to 338.15 K at constant ionic strength (I =  1.00 mol · kg  1). Additionally, the dependence of the solubility constant on the ionic strength has been investigated up to I =  3.00 mol · kg  1NaClO4at T =  298.15 K. The standard molar heat capacity Cp, mofunction fromT =  318.15 K to T =  418.15 K, as well as the heat of decomposition of hydrozincite, have been obtained from d.s.c. measurements. All experimental results have been simultaneously evaluated by means of the optimization routine of ChemSage yielding an internally consistent set of thermodynamic data (T =  298.15 K): solubility constant log * Kps 00 =  (9.0  ±  0.1), standard molar Gibbs energy of formationΔfGmo {Zn5(OH)6(CO3)2 }  =  (  3164.6  ±  3.0)kJ · mol  1, standard molar enthalpy of formation ΔfHmo{Zn5(OH)6(CO3)2 }  =  (  3584  ±  15)kJ · mol  1, standard molar entropy Smo{Zn5(OH)6(CO3)2 }  =  (436  ±  50)J · mol  1· K  1and Cp,mo / (J · mol  1· K  1)  =  (119  ±  11)  +  (0.834  ±  0.033)T / K. A three-dimensional predominance diagram is introduced which allows a comprehensive thermodynamic interpretation of phase relations in(Zn2 +  +  H2O  +  CO2) . The axes of this phase diagram correspond to the potential quantities: temperature, partial pressure of carbon dioxide and pH of the aqueous solution. Moreover, it is shown how the stoichiometric composition{n(CO3) / n(Zn)} of the solid compoundsZnCO3 and Zn5(OH)6(CO3)2can be checked by thermodynamically analysing the measured solubility data.  相似文献   

18.
The kinetics of the diazotization reaction of procaine in the presence of anionic micelles of sodium dodecyl sulfate (SDS) and cationic micelles of cetyltrimethyl ammonium bromide (CTAB), dodecyltrimethyl ammonium bromide (DDTAB) and tetradecyltrimethyl ammonium bromide (TDTAB) were carried out spectrophotometrically at λmax = 289 nm. The values of the pseudo first order rate constant were found to be linearly dependent upon the [NaNO2] in the concentration range of 1.0 × 10−3 mol dm−3 to 12.0 × 10−3 mol dm−3 in the presence of 2.0 × 10−2 mol dm−3 acetic acid. The concentration of procaine was kept constant at 6.50 × 10−5 mol dm−3. The addition of the cationic surfactants increased the reaction rate and gave plateau like curve. The addition of SDS micelles to the reactants initially increased the rate of reaction and gave maximum like curve. The maximum value of the rate constant was found to be 9.44 × 10−3 s−1 at 2.00 × 10−3 mol dm−3 SDS concentration. The azo coupling of diazonium ion with β-naphthol (at λmax = 488) nm was found to linearly dependent upon [ProcN2+] in the presence of both the cationic micelles (CTAB, DDTAB and TDTAB) and anionic micelles (SDS). Both the cationic and anionic micelles inhibited the rate of reactions. The kinetic results in the presence of micelles are explained using the Berezin pseudophase model. This model was also used to determine the kinetic parameters e.g. km, Ks from the observed results of the variation of rate constant at different [surfactants].  相似文献   

19.
Reactions of Be2+ and Mg2+ with O2– in molten eutectic mixture (CsCs + KCl + NaCl) (0.455:0.245:0.30) at T = 783 K were studied by a potentiometric method using Pt(O2)|ZrO2(Y2O3) indicator electrode. Addition of O2– ions to the melt containing Mg2+ results in precipitation of MgO (pKs,MgO = 11.89 ± 0.3, molality) whereas interaction of Be2+ with O2– is accompanied with sequential formation of Be2O2+ (pK = 15.68 ± 0.5, molality) and precipitation of BeO (pKs,BeO = 9.62 ± 0.3, molality). On the basis of the obtained and known data pKs,MgOT−1 dependence in molten (CsCs + KCl + NaCl) eutectic is constructed. The slope of the said dependence in T/K = (from 583 to 1073) range is in good agreement with the value predicted by the Shreder equation, that extends the range of use of the Shreder equation for predictions of metal oxide solubilities in molten halides.  相似文献   

20.
This paper reports a new solvent, room-temperature ionic liquid (RTIL), for the preparation of dodecanethiol self-assembled monolayers (C12SH-SAMs) on polycrystalline gold. The quality of C12SH-SAMs was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). From CV experiments, we find that the differential capacitance Cd values of the C12SH-SAM prepared in RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) containing 10 μL neat C12SH for 24 h (C12SH-SAMs[BMIM]PF6,10 μL,24 h) are independent of the scan rate, the effective thickness deff value and the average cant angle φ value of this monolayer are 18 ± 1 Å and 27 ± 4°, respectively. The difference value of the current density at −0.2 and 0.5 V (Δip) is only 0.73 ± 0.18 μA cm−2. EIS experiments show that the phase angle value at 1 Hz Φ1 Hz, the charge transfer resistance Rct value and surface coverage θ value of this C12SH-SAM are 88.2 ± 0.7°, 3.44 ± 1.91  cm2 and 99.998 ± 0.001%, respectively. These results indicate that high-quality C12SH-SAMs can be formed in [BMIM]PF6. In addition, the rate of formations of high-quality C12SH-SAMs in RTIL can be substantially improved by ultrasound.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号