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1.
The reaction of single crystals and powders of K2PtCl4 with hydrogen is studied by means of thermogravimetry (TG) at temperatures between 175 and 225°C and by optical microscopy. Two different mechanisms are observed. The rate of decomposition of single crystals is determined by the displacement of the reaction interface, which is similar in every crystallographic direction.The rate of decomposition of the powders is limited by the rate of nucleation in the powder particles. For both mechanisms the kinetic parameters are calculated. The activation energy for the displacement of the interface is much higher than the one necessary for nucleation.  相似文献   

2.
The study of the thermal decomposition of the tetrafluoroammonium salts (NF4)2NiF6 and NF4SbF6 by differential scanning calorimetry also gave enthalpies of decomposition for (NF4)2NiF6 and NF4SbF6 of 134.7 ± 13.0 kJ mol?1 and 245.6 ± 28.9 kJ mol?1 respectively. The corresponding standard enthalpies of formation are found to be ?1033 and ?1649 kJ mol?1 respectively.  相似文献   

3.
Thermal decomposition of formaldehyde diperoxide (1,2,4,5-tetraoxane) in aqueous solution with an initial concentration of 6.22 × 10?3 M was studied in the temperatures range from 403 to 439 K. The reaction was found to follow first-order kinetic law, and formaldehyde was the major decomposition product. The activation parameters of the initial step of the reaction (ΔH = 15.25 ± 0.5 kcal mol?1, ΔS = ?47.78 ± 0.4 cal mol?1K?1, E a = 16.09 ± 0.5 kcal mol?1) support a mechanism involving homolytic rupture of one peroxide bond in the 1,2,4,5-tetraoxane molecule with participation of the solvent and formation of a diradical intermediate.  相似文献   

4.
From measurements of the heats of iodination of CH3Mn(CO)5 and CH3Re(CO)5 at elevated temperatures using the ‘drop’ microcalorimeter method, values were determined for the standard enthalpies of formation at 25° of the crystalline compounds: ΔHof[CH3Mn(CO)5, c] = ?189.0 ± 2 kcal mol?1 (?790.8 ± 8 kJ mol?1), ΔHof[Ch3Re(CO)5,c] = ?198.0 ± kcal mol?1 (?828.4 ± 8 kJ mo?1). In conjunction with available enthalpies of sublimation, and with literature values for the dissociation energies of MnMn and ReRe bonds in Mn2(CO)10 and Re2(CO)10, values are derived for the dissociation energies: D(CH3Mn(CO)5) = 27.9 ± 2.3 or 30.9 ± 2.3 kcal mol?1 and D(CH3Re(CO)5) = 53.2 ± 2.5 kcal mol?1. In general, irrespective of the value accepted for D(MM) in M2(CO)10, the present results require that, D(CH3Mn) = 12D(MnMn) + 18.5 kcal mol?1 and D(CH3Re) = 12D(ReRe) + 30.8 kcal mol?1.  相似文献   

5.
In this study, we investigated the C? H bond activation of methane catalyzed by the complex [PtCl4]2?, using the hybrid quantum mechanical/effective fragment potential (EFP) approach. We analyzed the structures, energetic properties, and reaction mechanism involved in the elementary steps that compose the catalytic cycle of the Shilov reaction. Our B3LYP/SBKJC/cc‐pVDZ/EFP results show that the methane activation may proceed through two pathways: (i) electrophilic addition or (ii) direct oxidative addition of the C? H bond of the alkane. The electrophilic addition pathway proceeds in two steps with formation of a σ‐methane complex, with a Gibbs free energy barrier of 24.6 kcal mol?1, followed by the cleavage of the C? H bond, with an energy barrier of 4.3 kcal mol?1. The activation Gibbs free energy, calculated for the methane uptake step was 24.6 kcal mol?1, which is in good agreement with experimental value of 23.1 kcal mol?1 obtained for a related system. The results shows that the activation of the C? H bond promoted by the [PtCl4]2? catalyst in aqueous solution occurs through a direct oxidative addition of the C? H bond, in a single step, with an activation free energy of 25.2 kcal mol?1, as the electrophilic addition pathway leads to the formation of a σ‐methane intermediate that rapidly undergoes decomposition. The inclusion of long‐range solvent effects with polarizable continuum model does not change the activation energies computed at the B3LYP/SBKJC/cc‐pVDZ/EFP level of theory significantly, indicating that the large EFP water cluster used, obtained from Monte Carlo simulations and analysis of the center‐of‐mass radial pair distribution function, captures the most important solvent effects. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011  相似文献   

6.
The rate constant of the primary decomposition step was determined for four symmetrical and four unsymmetrical azoalkanes. From the experimental activation energies and some literature enthalpy data, the following enthalpies of formation of radicals and group contributions were calculated: ΔH? (CH3N2) = 51.5 ± 1.8 kcal mol?1, ΔH? (C2H5N2) = 44.8 ± 2.5 kcal mol?1, ΔH? (2?C3H7N2) = 37.9 ± 2.2 kcal mol?1, [NA-(C)] = 27.6 ± 3.7 kcal mol?1, [NA-(?A) (C)] = 61.2 ± 3.1 kcal mol?1.  相似文献   

7.
At room temperature and below, the proton NMR spectrum of N-(trideuteriomethyl)-2-cyanoaziridine consists of two superimposed ABC patterns assignable to two N-invertomers; a single time-averaged ABC pattern is observed at 158.9°C. The static parameters extracted from the spectra in the temperature range from –40.3 to 23.2°C and from the high-temperature spectrum permit the calculation of the thermodynamic quantities ΔH0 = ?475±20 cal mol?1 (?1.987 ± 0.084 kJ mol?1) and ΔS0 = 0.43±0.08 cal mol?1 K?1 (1.80±0.33 J mol?1 K?1) for the cis ? trans equilibrium. Bandshape analysis of the spectra broadened by non-mutual three-spin exchange in the temperature range from 39.4–137.8°C yields the activation parameters ΔHtc = 17.52±0.18 kcal mol?1 (73.30±0.75 kJ mol?1), ΔStc = ?2.08±0.50 cal mol?1 K?1 (?8.70±2.09 J mol?1 K?1) and ΔGtc (300 K) = 18.14±0.03 kcal mol?1 (75.90±0.13 kJ mol?1) for the transcis isomerization. An attempt is made to rationalize the observed entropy data in terms of the principles of statistical thermodynamics.  相似文献   

8.
It has been confirmed by 1H and 13C NMR spectroscopies that Sn(σ-C7H7)Ph3 undergoes either 1,4- or 1,5-shifts of the SnPh3 moiety around the cycloheptatrienyl ring with ΔH3 = 13.8 ± 0.4 kcal mol?1, ΔS3 = ?5.6 ± 1.2 cal mol?1 deg?1, and ΔG3300 = 15.44 ± 0.14 kcal mol?1. Similarly, (σ-5-cyclohepta-1,3-dienyl)triphenyltin undergoes 1,5-shifts with ΔH3 = 12.4 ± 0.6 kcal mol?1, ΔS3 = ?11.2 ± 1.8 cal mol?1 deg?1, and ΔG3300 = 15.76 ± 0.13 kcal mol?1. It is therefore probable that Sn(σ-5-C5H5)R3 and Sn(σ-3-indenyl)R3 do not undergo 1,2-shifts as previously suggested but really undergo 1,5-shifts.  相似文献   

9.
Azoethane was irradiated in the presence of carbon monoxide in the temperature range of 238 to 378 K. Kinetic parameters for the addition of ethyl radicals to carbon monoxide and for the decomposition of propionyl radicals were determined. The rate constants were found to be log k(cm3 mol?1 sec?1) = 11.19 - 4.8/θ and log k(sec?1) = 12.77 - 14.4/θ, respectively. Estimated thermochemical properties of the propionyl radical are ΔHf0 = -10.6 ± 1.0 kcal mol?1, S0 = 77.3 ± 1.0 cal K?1 mol?1, and D(C2H5CO? H) = 87.4 kcal mol?1.  相似文献   

10.
The dehydration of K4[Ni(NO2)6]-H2O and the simultaneous linkage isomerization have been studied using differential scanning calorimetry. Two types of behavior were found for different samples. In one case, complete dehydration occurs and there is partial conversion of N-bonded nitrite to the O-bonded form. In the other case, only about 20% of the water is removed during the isomerization. The enthalpy change is estimated to be 3.5 kcal mol?1 for each nitrite converted and 9.6 kcal mol?1 for the dehydration.  相似文献   

11.
The microwave spectrum of N2D4 has been observed and analyzed. Based on five low-J rotational transitions the effective rotational constants are: A = 74712.9 ± 1.9 MHz, B = 18500.42 ± 0.46 MHz, and C = 18439.91 ± 0.46 MHz. The quadrupole coupling constants of the 14N nuclei are Xaa = 4.23 ± 0.04 MHz, Xbb = 1.98 ± 0.05 MHz, and Xcc = ?2.25 ± 0.05 MHz. Using the observed ground state inversion splittings for N2D4 and N2H4 the barrier to inversion of a single amino group is computed to be 5.00 kcal mol?1.  相似文献   

12.
The kinetics of reduction of hexachloroplatinate(IV) by dithionite have been examined spectrophotometrically in sodium acetate?Cacetic acid buffer medium in the temperature range 288?C303?K. The reaction is first order in both platinum(IV) species and dithionite. H+ ion has an inhibiting effect on the rate in the pH range 3.68?C4.80. The pseudo-first order rate constant increased upon increasing both ionic strength and dielectric constant. The suggested mechanism involves an initial transition state between two like charged ions, which then decomposes to give SO3 2? through the intermediate formation of free radicals. The presence of free radicals was confirmed by performing the reaction in the presence of acrylamide. PtCl6 2? is finally reduced to PtCl4 2?, as confirmed by thermogravimetric analysis and IR spectrophotometry. The values of ?H?? and ?S?? associated with the rate-determining step have been calculated as 33?±?4?kJ?mol?1 and ?141?±?7?JK?mol?1, respectively. The values of ?H° and ?S° for the dissociation of HS2O4 ? are 16?±?4?kJ?mol?1 and ?14?±?7?JK?mol?1, respectively.  相似文献   

13.
The rate constant for the reaction NH3 + OH → NH2 + H2O was determined by the comparison of the calculated induction period data with experiments by the shock tube technique in the range 1360–1840 K, for NH3-H2-O2-Ar mixtures. The rate constants can be represented by the expression k = 1012.49±0.04exp[(?1.95±0.15) kcal/,RT] cm3 mol?1 s?1.  相似文献   

14.
15.
The kinetics of decomposition of [Alg · Mn VIO42?] intermediate complex have been investigated spectrophotometrically at a constant ionic strength of 0.5 mol dm?3. The decomposition reaction was found to be first-order in the intermediate concentration. The results showed that the rate of reaction was base-catalyzed. The kinetic parameters have been evaluated and found to be ΔS? = ?103.88±6.18 J mol?1 K?1, ΔH? = 51.61 ± 1.02 kJ mol?1, and ΔG? = 82.57 ± 2.86 kJ mol?1, respectively. A reaction mechanism consistent with the results is discussed. © 1993 John Wiley & Sons, Inc.  相似文献   

16.
The rate of decomposition of 2-pentoxy radical to acetaldehyde and n-propyl radical has been studied in the presence of NO in competition with nitrite formation at and above 200 kPa pressure over the temperature range of 363-413 K. The rate coefficient for the decomposition is given as log(kla/s?1) = (14.2 ± 0.4) - (13.8 ± 0.8) kcal mol?1/RT ln 10. Isomerization of 2-pentoxy radical by 1,5-hydrogen shift has been investigated in the range 279–385 K in competition with the decomposition in a static system, with methyl radicals present in high concentration to ensure trapping of the isomerized free radicals. The rate coefficient for isomerization is given as log(k3/s?1) = (11.1 ± 0.7) - (9.5 ± 1.1) kcal mol?1/RT ln 10. The implications of the results for atmospheric chemistry are discussed.  相似文献   

17.
Calorimetric measurements of the enthalpy of reaction of WO3(c) with excess OH?(aq) have been made at 85°C. Similar measurements have been made with MoO3(c) at both 85 and 25°C, to permit estimation of ΔH°=?13.4 kcal mol?1 for the reaction WO3(c)+2OH?(aq)=WO2?4(aq)+H2O(liq) at 25°C. Combination of this ΔH° with ΔH°f for WO3(c) leads to ΔH°f=?256.5 kcal mol?1 for WO2?4(aq). We also obtain ΔH°f=?269.5 kcal mol?1 for H2WO4(c). Both of these values are discussed in relation to several earlier investigations.  相似文献   

18.
The kinetics of the reaction between CH3 and HCl was studied in a tubular reactor coupled to a photoionization mass spectrometer. Rate constants were measured as a function of temperature (296–495 K) and were fitted to an Arrhenius expression: k1 = 5.0(±0.7) × 10?13 exp{?1.4(±0.3) kcal mol?1/RT} cm3 molecule?1 s?1. This information was combined with known kinetic parameters of the reverse reaction to obtain Second Law determinations of the methyl radical heat of formation {34.7(±0.6) kcal mol?1} and entropy {46(±2) cal mol?1 K?1} at 298 K. Using the known entropy of CH3, a more accurate Third Law determination of the CH3 heat of formation at this temperature was also obtained {34.8(±0.3) kcal mol?1}. The values of k1 obtained in this study are between those reported in prior investigations. The results were also used to test the accuracy of the thermochemical information which can be obtained from kinetic studies of R + HX (X = Cl, Br, I) reactions of the type described here.  相似文献   

19.
The enthalpy of formation of ammonium tungsten bronze, (NH4)0.25WO3(s), at 298.15 K has been determined by solution calorimetry. The value obtained for formation from NH3(g), H2(g) and WO3(s) was ?25.7 ± 0.8 k1 mol?1. The stability of the bronze towards decomposition and oxidation is discussed.  相似文献   

20.
The heat of formation of benzophenone oxide, Ph2CO2, was measured using photoacoustic calorimetry. The enthalpy of the reaction Ph2CN2 + O2 → Ph2CO2 + N2 was found to be ?48.0 ±0.8 kcal mol?1 and ΔHf(Ph2CN2) was determined by measuring the reaction enthalpy for Ph2CN2 + EtOH → Ph2CHOEt + N2 (?53.6 ±1.0 kcal mol?1). Taking ΔHf(PhCHOEt) = ?10.6 kcal mol?1 led to ΔHf(Ph2CN2) = 99.2 ± 1.5 kcal mol?1 and hence to ΔHf(Ph2CO2) = 51.1 ± 2.0 kcal mol?1. The results imply that the self-reaction of benzophenone oxide i.e., 2Ph2CO2 → 2Ph2CO + O2 is exothermic by ?76.0 ±4.0 kcal mol?1.  相似文献   

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