共查询到20条相似文献,搜索用时 15 毫秒
1.
对于非等温过程中的动力学方程,正确的Arrhenius方程的温度积分应该是从T2到T1,但是许多动力学方程中的温度积分是从T到0 K,例如Ozawa等方程。我们的研究指出对于某些反应,这些方程中的活化能存在较大的误差,因此我们提出了一个新的动力学方程。凭借等转化率法,应用新的方程可以精确求解线性或非线性加热过程中化学反应的活化能。用新方程对2个经典反应(聚酰胺的热裂解和一水草酸钙的热分解)的研究表明:Ozawa方程的活化能有时是精确的,有时偏差太大。 相似文献
2.
Kawthar Bouchemal Patrick Couvreur Samia Daoud-Mahammed Jacques Poupaert Ruxandra Gref 《Journal of Thermal Analysis and Calorimetry》2009,98(1):57-64
In this study, the entrapment of benzophenone (BZ) into supramolecular nanoassemblies prepared by mixing two water-soluble
associative polymers (i.e. polymerized β-CD (pβ–CD) and dextran grafted with lauryl-side chains (MD)) has been investigated
by using isothermal titration microcalorimetry (ITC) and molecular modeling. ITC experiments have been performed at various
temperatures (4 °C (277 K), 25 °C (298 K), and 37 °C (310 K)) to evaluate the interaction of BZ with pβ–CD in comparison with
β-CD. The inclusion complexation for both β-CD/BZ and pβ–CD/BZ interactions was entropy-driven (|ΔH| < |TΔS|) when the temperature of the experiment was low (4 °C) and enthalpy-driven (|ΔH| > |TΔS|) with minor entropic contribution when the temperature was increased (25 and 37 °C). Using all the thermodynamic data obtained
for β-CD/BZ and pβ–CD/BZ interactions when the temperature of the experiment was varied, the
\Updelta H = f(T\Updelta S ) \Updelta H\; = \;f(T\Updelta S ) plot was perfectly linear, which reflected an enthalpy–entropy compensation process. Finally, the combination of ITC data
with molecular modeling provided consistent information in regard to the location of MD side chains and BZ inside the cyclodextrin
cavity, as well as concerning the stability of the nanoassemblies loaded with BZ. 相似文献
3.
Yanchun Li Yi Cheng Yinghua Ye Ruiqi Shen 《Journal of Thermal Analysis and Calorimetry》2010,102(2):605-608
The relative errors (e%) in the determination of the activation energy from the slope of the Kissinger straight line ln(β/βT
p2) vs. 1/T
p (β is the heating rate) are in-depth discussion. Our work shows that the relative errors is a function containing the factors
of x
p and Δx
p, not only x
p (x
p = E/RT
p, E is the activation energy, T
p is the temperature corresponding to maximum process rate, R is the gas constant). The relative error between E
k and E
p will be smaller with the increase of the value of x and/or with the decrease of the value of Δx. For a set of different heating rates in thermal analysis experiments, the low and close heating rates are proposed from
the kinetic theory. 相似文献
4.
A modification of a variation principle due to Delves, is derived which permits the direct calculation of energy differences between states of two different Hamiltonians: [Δ ??] = 〈X0| ??x – Wx|X1〉 – 〈Y0|??y – Wy|y1〉 + 〈X0| Δ ??|Y0〉 · 〈X0| Y0〉?1. Δ ?? = ??y – ??x, |X0〉 and |Y0〉 are the wave functions for the X and Y states and |X1〉 and |Y1〉 are functions defined in the text. The principle is applied to a few simple examples. 相似文献
5.
Influence of the Degree of Dehydroxylation of Kaolinite on the Properties of Aluminosilicate Glasses
The degree of dehydroxylation of kaolinite, DTG and DIR, respectively, is characterized by thermogravimetric analysis (TG) and Fourier transform infrared spectroscopy (FTIR). The
relation between DTG and DIR based on the infrared absorptions at 3600–3700, 915, 810, and 540 cm−1 is established. Three regions can clearly be distinguished: the dehydroxylation region (DTG<0.9), the metakaolinite region (0.9<DTG<1) and the ‘spinel’ region(DTG=1). The effect of the degree of dehydroxylation of kaolinite on the amount of reactive material is measured by the reaction
enthalpy, ΔH, of the low-temperature reaction of the dehydroxylated kaolinite with a potassium silicate solution using differential scanning
calorimetry (DSC). |ΔH| increases almost linearly with DTG in the dehydroxylation region. In the metakaolinite region, ΔH and thus the amount of reactive material, becomes constant. |ΔH| is sharply decreasing when metakaolinite transforms into other phases in the ‘spinel’ region. No significant differences
in the reactivity of the dehydroxylates is detected with DSC. According to FTIR, the use of partially dehydroxylated kaolinite
is not influencing the molecular structure of the low-temperature synthesized aluminosilicates, but residual kaolinite is
retrieved as an additive.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
6.
Rois Benassi 《Theoretical chemistry accounts》2001,106(4):259-263
In order to calculate more accurately the enthalpies of formation, ΔH
f°(298 K), for large molecules using the CBS-4M method, a new formulation of the empirical higher-level correction to the energy
is proposed: ΔE=a|S|2
i
i
I
i
i
+b(n
α+n
β)+cΔ<S
2>+Σn
i
d
i
. The new methodology (CBS-4MB) applied to a set of 114 molecules of different size significantly decreases the mean absolute
deviation from 3.78 to 2.06 kcal/mol.
Received: 7 February 2001 / Accepted: 5 April 2001 / Published online: 13 June 2001 相似文献
7.
Gibbs energies of activation for viscous flow of binary water (1) + dimethyl sulfoxide (2) mixtures, Δμ
12○, and of lysozyme (3) in corresponding ternary mixtures, Δμ
3○, were determined at 298.15 K. The binary mixtures have a maximum in the value of the excess quantity for Δμ
12○ at a dimethyl sulfoxide mole fraction of x
2≈0.31. The values of Δμ
3○ are larger than Δμ
12○ at all values of x
2, even when normalized by their molar volumes, suggesting that the solvents interact more strongly with lysozyme than with
themselves. The values of Δμ
3○ significantly increased in the range of x
2=0.3 to 0.4 because of an increase in solvent-lysozyme interactions, which resulted from an increase in the accessible surface
area of lysozyme that was exposed by its unfolding. The mean value obtained for Δμ
3○ per amino acid of lysozyme at x
2=0.2 is greater than that for hydrophobic amino acids, indicating that the solvent interacts with hydrophilic amino acids
more strongly than with hydrophobic ones. 相似文献
8.
The minimal energy conformations of o-benzosemiquinone anion radicals in the solvents containing the alkali metals and the alkali earth metals were calculated by using the INDO method and the molecular geometry adjusting method. Our previous calculations of o-benzosemiquinone anion radical in the lithium ion solution showed that the total energy of the minimal energy conformation in the case of the assignment |A3| > |A4| were lower by approximately 320 kcal/mol than that in the case of the assignment |A3| > |A4|. Therefore, the calculations of the minimal energy conformations of o-benzosemiquinone anion radicals in the metal ion solutions were carried out in the cases of the assignment |A3| > |A4|. The conformations in both assignments A3 < A4 < 0 and (A3 < 0 < A4 and |A3| > |A4|) were calculated. Although the metal ions were not explicitly contained in the molecular geometries, the minimal energy conformations are considered to be close to the real minimal energy conformations of o-benzosemiquinone anion radicals in the metal ion solutions. The C? O bond lengths has a good positive rank correlation with the stabilities of o-benzosemiquinone radicals in the divalent metal ion solutions and the bond angles ∠C3C4H4 had a good negative rank correlation with those stabilities. 相似文献
9.
Dolunay Şakar 《Monatshefte für Chemie / Chemical Monthly》2006,137(7):919-928
Summary. Intrinsic viscosities, [η], of poly(p-chlorostyrene) (PPCS) in diethylene glycol monobutyl ether (DGMBE) which exhibits an exothermic solubility behavior with the polymer were measured using an Ubbelohde type capillary viscometer
between 25 and 85°C. Polymer solvent interaction parameters at infinite dilution (χ1), exchange energy parameter
, exchange enthalpy (X12), and entropy parameters (Q12), of the PPCS/DGMBE pair were found at studied temperature range according to equation-of-state theory.
In the blob theory, dependence of [η] on temperature can be scaled by a master curve in a plot of αη3|τ|M1/2 versus |τ|M1/2 as the polymer coil contracts below the Θ-point, however, it can be scaled by a master curve in a plot of αη−5|τ|M1/2 versus |τ|M1/2 as the polymer coil expands above the Θ-point in an endothermic solubility behavior. Since the studied PPCS/DGMBE system represents exothermic solubility behavior, the master curves of the system were plotted in αη3|τ|M1/2 versus |τ|M1/2 as the polymer coil contracts above the Θ-point and in αη−5|τ|M1/2 versus |τ|M1/2 as the polymer coil expands below the Θ-point. The universal plots of αη(N/Nc)1/6 versus N/Nc and αη(N/Nc)−1/10 versus N/Nc were plotted above and below Θ-point, respectively. 相似文献
10.
Roman F. Nalewajski 《Journal of Chemical Sciences》2005,117(5):455-466
The “geometric” interpretation of the electronic density displacements in the Hilbert space is given and the associated projection-operator
partitioning of the hardness and softness operators (kernels) is developed. The eigenvectors |?〉= |α〉 of the hardness operator
define the complete (identity) projector P =Σα| α〉〈α | = 1 for general density displacements, including thecharge-transfer (CT) component, while the eigenvectors |i〉= |i〉 of the linear response operator determine thepolarizational P-projector, Pp = Σi |i〉〈i| . Their difference thus defines the complementary CT-projector: PCT = 1-PP. The complete vector space for density displacements can be also spanned by supplementing the P-modes with the homogeneous
CT-mode. These subspaces separate the integral (normalization) and local aspects of density shifts in molecular systems. 相似文献
11.
Nopsiri Chaiyo Rangson Muanghlua Surasak Niemcharoen Banjong Boonchom Panpailin Seeharaj Naratip Vittayakorn 《Journal of Thermal Analysis and Calorimetry》2012,107(3):1023-1029
The thermal transformation of Na2C2O4 was studied in N2 atmosphere using thermo gravimetric (TG) analysis and differential thermal analysis (DTA). Na2C2O4 and its decomposed product were characterized using a scanning electron microscope (SEM) and the X-ray diffraction technique
(XRD). The non-isothermal kinetic of the decomposition was studied by the mean of Ozawa and Kissinger–Akahira–Sunose (KAS)
methods. The activation energies (E
α) of Na2C2O4 decomposition were found to be consistent. Decreasing E
α at increased decomposition temperature indicated the multi-step nature of the process. The possible conversion function estimated
through the Liqing–Donghua method was ‘cylindrical symmetry (R2 or F1/2)’ of the phase boundary mechanism. Thermodynamic functions (ΔH*, ΔG* and ΔS*), calculated by the Activated complex theory and kinetic parameters, indicated that the decomposition step is a high energy
pathway and revealed a very hard mechanism. 相似文献
12.
Dolunay ?akar 《Monatshefte für Chemie / Chemical Monthly》2006,27(3):919-928
Intrinsic viscosities, [η], of poly(p-chlorostyrene) (PPCS) in diethylene glycol monobutyl ether (DGMBE) which exhibits an exothermic solubility behavior with the polymer were measured using an Ubbelohde type capillary viscometer
between 25 and 85°C. Polymer solvent interaction parameters at infinite dilution (χ1), exchange energy parameter
([`(X)]12)(\bar{X}_{12})
, exchange enthalpy (X12), and entropy parameters (Q12), of the PPCS/DGMBE pair were found at studied temperature range according to equation-of-state theory.
In the blob theory, dependence of [η] on temperature can be scaled by a master curve in a plot of αη3|τ|M1/2 versus |τ|M1/2 as the polymer coil contracts below the Θ-point, however, it can be scaled by a master curve in a plot of αη−5|τ|M1/2 versus |τ|M1/2 as the polymer coil expands above the Θ-point in an endothermic solubility behavior. Since the studied PPCS/DGMBE system represents exothermic solubility behavior, the master curves of the system were plotted in αη3|τ|M1/2 versus |τ|M1/2 as the polymer coil contracts above the Θ-point and in αη−5|τ|M1/2 versus |τ|M1/2 as the polymer coil expands below the Θ-point. The universal plots of αη(N/Nc)1/6 versus N/Nc and αη(N/Nc)−1/10 versus N/Nc were plotted above and below Θ-point, respectively. 相似文献
13.
The effects of Co alloying to Pt catalyst and Nafion pretreatment by NaClO4 solution on the rate-determining step (RDS) of oxygen reduction at Nafion-impregnated Pt-dispersed carbon (Pt/C) electrode
were investigated as a function of the potential step ΔE employing potentiostatic current transient (PCT) technique. For this purpose, the cathodic PCTs were measured on the pure
Nafion-impregnated and partially Na+-doped Nafion-impregnated Pt/C and PtCo/C electrodes in an oxygen-saturated 1 M H2SO4 solution and analyzed. From the shape of the cathodic PCTs and the dependence of the instantaneous current on the value of
ΔE, it was confirmed that oxygen reduction at the pure Nafion-impregnated electrodes is controlled by charge transfer at the
electrode surface mixed with oxygen diffusion in the solution below the transition potential step |ΔE
tr| in absolute value, whereas oxygen reduction is purely governed by oxygen diffusion above |ΔE
tr|. On the other hand, the RDS of oxygen reduction at the partially Na+-doped Nafion-impregnated electrodes below |ΔE
tr| is charge transfer coupled with proton migration, whereas above |ΔE
tr|, it becomes proton migration in the Nafion electrolyte instead of oxygen diffusion. Consequently, it is expected in real
fuel cell system that the cell performance is improved by Co alloying since the electrode reaches the maximum diffusion (migration)
current even at small value of |ΔE|, whereas the cell performance is aggravated by Nafion pretreatment due to the decrease in the maximum diffusion (migration)
current. 相似文献
14.
Almuth Läuter Prakash D. Naik Jai P. Mittal Hans-Robert Volpp Jürgen Wolfrum 《Research on Chemical Intermediates》2007,33(6):513-522
The vibrationally-mediated H2O gas-phase photodissociation was studied at a photolysis wavelength of 248 nm. Single rotational states of the |03−〉|2〉 and |04−〉 H2O overtone vibrations were prepared by laser photoexcitation around 720 nm. H atoms formed in the photodissociation of the
H2O (|04−〉
= 313) were detected by Lyman-α laser-induced fluorescence spectroscopy with sub-Doppler resolution to determine their translational energy. The present
result confirms that in the dissociation process the major part (ca. 93%) of the available energy is released as relative translational energy of the nascent H + OH photofragments, in agreement
with earlier complementary measurements (R. L. Vander Wal, J. L. Scott and F. F. Crim, J. Chem. Phys.
94, 1859 (1991)), where the internal excitation of the OH product radical was investigated at different photolysis wavelengths. 相似文献
15.
A model was proposed to calculate some thermodynamic parameters for the acid dissolution process of a bentonite containing
a calcium-rich smectite as clay mineral along with quartz, opal and feldspar as impurities. The bentonite sample was treated
with H2SO4 by applying dry method in the temperature range 50–150°C for 24 h. The acid content in the dry bentonite-sulphuric acid mixture
was 45 mass%. The total content (x) of Al2O3, Fe2O3 and MgO remained in the undissolved sample after treatment was taken as an equilibrium parameter. An apparent equilibrium
constant, K
a, was calculated for each temperature by assuming K
a=(x
m−x)/x where x
m is the total oxide content of the natural bentonite. Also, an apparent change in Gibbs free energy, ΔG
ao, was calculated for each temperature by using the K
a value. The graphs of lnK
a
vs. 1/T and ΔG
ao
vs. T were drawn and then the real change in both the enthalpy, ΔH
o and the entropy, ΔS
o, values were calculated from the slopes of the straight lines, respectively. Inversely, real ΔG
o and K values were calculated from the real ΔH
o and ΔS
o values through ΔG
o = −RT ln K = ΔH
o − TΔS
o equation. The best ΔH
o and ΔS
o fittings to this relation were found to be 65687 J mol−1 and 164 J mol−1K−1, respectively. 相似文献
16.
D. V. Safronov I. A. Stenina A. V. Maksimychev S. L. Shestakov A. B. Yaroslavtsev 《Russian Journal of Inorganic Chemistry》2009,54(11):1697-1703
NASICON materials of composition Li1 + x
Zr2 − x
In
x
(PO4)3(x = 0–1) were synthesized. The phase constitution, particle size, and conductivity of these materials were studied as s function
of synthesis temperature. High-temperature X-ray powder diffraction was used to study phase transitions in the materials synthesized.
Low levels (x ≤ 0.1) partial substitution of indium for zirconium considerably increase the lithium ion conductivity and reduce the activation
energy for conduction compared to the parent compound. 相似文献
17.
The basic kinetic parameters of thermal polymerization of hexafluoropropylene, namely, general rate constants, degree of polymerization,
and their temperature and pressure dependences in the range of 230–290 °C and 2–12 kbar (200–1200 MPa) were determined. The
activation energy (E
act = 132±4 kJ mol−1) and activation volume (ΔV
0
≠ = −27±1 cm3 mol−1) were calculated. The activation energy of thermal initiation of polymerization was estimated. The reaction scheme based
on the assumption about a biradical mechanism of polymerization initiation was proposed. 相似文献
18.
Luigi Falciola Patrizia R. Mussini Torquato Mussini 《Journal of solution chemistry》2000,29(12):1199-1210
Determination of primary standards for pH measurements in glycerol + water solventmixtures has been carried out based on reversible emf measurements of the cellPt|H2|KHPh (m
PS) + KCl (m
Cl)|AgCl|Ag|Ptwhere KHPh denotes the potassium hydrogen phthalate buffer solution of molalitym
PS = 0.05 mol-kg–1, at glycerol mass fractions w
G = 0.2 and 0.4, within thetemperature range –10 to 40°C. A multilinear regression procedure as a functionof electrolyte molality, glycerol mass fraction w
G, and temperature T has beenapplied for the data processing leading to the values of primary standards pHPS.These can be represented by the following regression equationpHPS = (4.007037±0.001113) + (3.55844±0.01776)x
G+(0.39622±0.01410)z + (4.3084±0.3377)z
2– (50.66±10.53)x
G
z
2 + (457.10±78.48)x
G
2
z
2where z = (T – 298.15)/298.15. Parallel values of the first ionization constantof o-phthalic acid (H2Ph; benzene-1,2-dicarboxylic acid, the parent acid of KHPh),which are essential for the above calculations, have been determined fromreversible emf measurements of the cellPt|H2|H2Ph (m
1) + KHPh (m
2) + KCl (m
3)|AgCl|Ag|Ptover the range of solvent composition and temperatures mentioned above. 相似文献
19.
The initial reaction rate (V
0) for the esterification reaction of feruloyl esterase (FAE-II) at different temperatures (288, 298, 308, 318, 328, 338, 348,
and 358 K) and various ethyl ferulate concentrations [(2, 4, 6, 8, 10, 12, 14, and 16) × 10−4 mol l−1 of ethyl ferulate in water] were determined. The Lineweaver-Burk double reciprocal plot yielded the kinetic parameters (maximal
velocity V
max, Michaelis constant K
m, and second order rate constant V/K). The effects of temperature on those 3 kinetic parameters were presented and discussed. The thermodynamic parameters ΔH* (enthalpy of activation), ΔG* (free energy of activation), ΔS* (entropy of activation), ΔG
E-S (free energy change of substrate binding), ΔG
E-T (free energy change of transition state formation), related to that biochemical process were determined and discussed from
van’t Hoff plot, Arrhenius plot, and Eyring plot. 相似文献
20.
Banjong Boonchom 《Journal of Thermal Analysis and Calorimetry》2009,98(3):863-871
The thermal decomposition of magnesium hydrogen phosphate trihydrate MgHPO4 · 3H2O was investigated in air atmosphere using TG-DTG-DTA. MgHPO4 · 3H2O decomposes in a single step and its final decomposition product (Mg2P2O7) was obtained. The activation energies of the decomposition step of MgHPO4 · 3H2O were calculated through the isoconversional methods of the Ozawa, Kissinger–Akahira–Sunose (KAS) and Iterative equation,
and the possible conversion function has been estimated through the Coats and Redfern integral equation. The activation energies
calculated for the decomposition reaction by different techniques and methods were found to be consistent. The better kinetic
model of the decomposition reaction for MgHPO4 · 3H2O is the F
1/3 model as a simple n-order reaction of “chemical process or mechanism no-invoking equation”. The thermodynamic functions (ΔH*, ΔG* and ΔS*) of the decomposition reaction are calculated by the activated complex theory and indicate that the process is non-spontaneous
without connecting with the introduction of heat. 相似文献