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1.
The theoretical relations of thermodynamic properties, the equilibrium constant and reactant size in nanosystem are described. The effects of size on thermodynamic properties and the equilibrium constant were studied using nanosize zinc oxide and sodium bisulfate solution as a reaction system. The experimental results indicated that the molar Gibbs free energy, the molar enthalpy and the molar entropy of the reaction decrease, but the equilibrium constant increases with decreasing reactant size. Linear trends were observed between the reciprocal of size for nano-reactant and thermodynamic variable, which are consistent with the theoretical relations. 相似文献
2.
《Comptes Rendus de l''Academie des Sciences Series IIB Mechanics Physics Astronomy》2000,3(8):667-674
Reaction of pentadienyl radicals (C5H7) with O2 has been studied by a combination of pulsed laser photolysis and photoionization mass spectrometry. These radicals could be generated either by the photolysis of 1,3-pentadiene or by the two-step reaction of carbon tetrachloride photolysis followed by the H-atom abstraction reaction of Cl atom with 1,4-pentadiene. The equilibrium between pentadienyl radicals, O2 and pentadienylperoxy radicals could be observed over the range 268–308 K. An analysis of the temporal signal of pentadienyl radicals was used to evaluate the equilibrium constant. Third-law analysis was used to evaluate the enthalpy change for the reaction C5H7 + O2 ⇌ C5H7O2. The observed CO bond energy in the C5H7O2 adduct was found to be 56.0 ± 2.2 kJ·mol–1, which is lower than the values of peroxy radicals formed with allyl and cyclohexenyl radicals which have an allylic resonance structure. 相似文献
3.
Stephen M. Gross W. Clayton Bunyard Karen Erford George W. Roberts Douglas J. Kiserow Joseph M. DeSimone 《Journal of polymer science. Part A, Polymer chemistry》2002,40(1):171-178
Despite the industrial significance of poly(bisphenol A carbonate), there is a scarcity of open literature on the equilibrium of the melt‐phase process. In fact, the equilibrium constant (Keq) for this reaction has never been measured directly. This article describes a process on the basis of NMR for the measurement of Keq for the reaction between bisphenol A and diphenyl carbonate in the presence and absence of a catalyst. The apparent enthalpy and entropy were calculated using a van't Hoff plot. Decomposition of bisphenol A is a common side reaction in the melt‐phase reaction performed at high temperatures in the presence of catalyst. The effect of these side reactions on the Keq in the presence of catalyst is determined. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 171–178, 2002 相似文献
4.
Using the recently detected intense UV absorption spectrum of it has been established that SiCl2 reacts with nitric oxide in the gas phase with a bimolecular rate constant, k(SiCl2+NO), of (1.6±0.1)×109 M−1s−1 at 25°C. 相似文献
5.
Concentration formation constants for the 18-crown-6-sodium ion complex in anhydrous methanol solutions were measured as a function of the ionic strength of the solution. The Kc values remained reasonably constant for Ic ? 0.05 mol dm?3 At higher ionic strengths the Kc values begin to decrease. The infinite-dilution formation constant was 2.2 × 104. 相似文献
6.
A sensitive hydrazine sensor has been fabricated using copper oxide nanoparticles modified glassy carbon electrode (GCE) to
form nano-copper oxide/GCE. The nano-copper oxide was electrodeposited on the surface of GCE in CuCl2 solution at −0.4 V and was characterized by Scanning electron microscopy and X-ray diffraction. The prepared modified electrode
showed a good electrocatalytic activity toward oxidation of hydrazine. The electrochemical behavior of hydrazine on nano-copper
oxide/GCE was explored. The oxidative current increased linearly with improving concentration of hydrazine on nano-copper
oxide/GCE from 0.1 to 600 μM and detection limit for hydrazine was evaluated to be 0.03 μM at a signal-to-noise ratio of 3.
The oxidation mechanism of hydrazine on the nano-copper oxide/GCE was also discussed. The fabricated sensor could be used
to determine hydrazine in real water. 相似文献
7.
Delbos E Fittschen C Hippler H Krasteva N Olzmann M Viskolcz B 《The journal of physical chemistry. A》2006,110(9):3238-3245
The kinetics of the CH2CHO + O2 reaction was experimentally studied in two quasi-static reactors and a discharge flow-reactor at temperatures ranging from 298 to 660 K and pressures between 1 mbar and 46 bar with helium as the bath gas. The CH2CHO radicals were produced by the laser-flash photolysis of ethyl vinyl ether at 193 nm and by the reaction F + CH3CHO, respectively. Laser-induced fluorescence excited at 337 or 347.4 nm was used to monitor the CH2CHO concentration. The reaction proceeded via reversible complex formation with subsequent isomerization and fast decomposition: CH2CHO + O2 <= => O2CH2CHO --> HO2CH2CO --> products. The rate coefficients for the first and second steps were determined (k1, k-1, k2) and analyzed by a master equation with specific rate coefficients from the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Molecular and transition-state parameters were obtained from quantum chemical calculations. A third-law analysis led to the following thermodynamic parameters for the first step: Delta(R)S degrees 300K(1) = -144 J K(-1) mol(-1) (1 bar) and Delta(R)H degrees 300K(1) = (-101 +/- 4) kJ mol(-1). From the falloff analysis, the following temperature dependencies for the low- and high-pressure limiting rate coefficients were obtained: k1(0) = 5.14 x 10(-14) exp(210 K/T) cm(-3) s(-1); k1(infinity) = 1.7 x 10(-12) exp(-520 K/T) cm(-3) s(-1); and k2(infinity) = 1.3 x 10(12) exp[-(82 +/- 4) kJ mol(-1)/RT] s(-1). Readily applicable analytical representations for the pressure and temperature dependence of k1 were derived to be used in kinetic modeling. 相似文献
8.
Alain H. Roux Daniel Hétu Gérald Perron Jacques E. Desnoyers 《Journal of solution chemistry》1984,13(1):1-25
Mixed micelles can be formed in water between various pairs of hydrophobic solutes such as surfactants, alcohols and hydrocarbons. These systems can often be studied through the thermodynamic functions of transfer of one of the solutes, usually kept near infinite dilution, from water to an aqueous solution of the other solute. When mixed micelles are formed, these functions change significantly, and often go through extrema, in the region where the binary system micellizes or undergoes some microphase transition.Three main effects are responsible for the observed trends: pair-wise interactions between both solutes in the monomeric form, a distribution of the reference solute between the aqueous and micellar phases and a shift in the monomer-micelle equilibrium in the vicinity of the reference solute. Simple equations can be derived for these three effects which can account for the sign and magnitude of the observed trends using parameters which are derived for the most part from the two binary systems. 相似文献
9.
10.
The absolute rate constanss for the gas-phase reactions of 1,1-dichlorosilylene with carbon monoxide and nitrous oxide have been determined using the flash photolysts-kinetic absorpiton spectroscopy technique. The bimolecular rate constant values at 25° C are: $$\begin{gathered} k\left( {Cl_2 Si + CO} \right) = \left( {6.3 \pm 0.7} \right) \times 10^8 M^{ - 1} s^{ - 1} \hfill \\ k\left( {Cl_2 Si + N_2 O} \right) = \left( {5.7 \pm 0.3} \right) \times 10^8 M^{ - 1} s^{ - 1} \hfill \\ \end{gathered} $$ 相似文献
11.
Virgil Percec Howard G. Schild Jos M. Rodriguez-Parada Coleen Pugh 《Journal of polymer science. Part A, Polymer chemistry》1988,26(3):935-951
The interpolymeric electron donor–acceptor (EDA) complex of donor poly[(N-ethylcarbazol-3-yl)methyl methacrylate] (PHMCM-2) with acceptor poly-(2-[(3,5-dinitrobenzoyl)oxy]ethyl methacrylate) (PDNBM-2) presents a single glass transition temperature and a decomplexation endotherm on differential scanning calorimetric (DSC) thermograms. This system is considered a “polymer blend model” which exhibits a lower critical solution temperature (LCST). Phase separation of this blend is kinetically controlled and positive deviations of the glass transition temperatures from weight average values suggest that it behaves as a thermally reversible crosslinked network. Calorimetric methods to determine the heats of mixing of small molecule complexes in solution were adapted for this solid state blend to estimate the equilibrium constant (Keq) and other thermodynamic parameters. Applying a computer iterative procedure and assuming 1 : 1 stoichiometry, a least-squares fit was found for several different donor molecular weights with three different high molecular weight acceptors. At moderate molecular weights, Keq rises to represent saturation fractions near unity as found in biological systems. Keq decreases for higher molecular weights, possibly due to trapped chain entanglements. These results are supported by a composition-independent, “horizontal line” phase diagram, thus resembling the completely complexed/denaturation process in DNA. 相似文献
12.
E. A. Venediktov E. Yu. Tulikova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2013,87(4):634-637
The axial interaction of chloroindiumtetraphenylporphyrin with pyridine is studied in a mixed binary benzene-pyridine solvent of variable composition. Thermodynamic parameters of the process are determined. It is concluded on the basis of the results that the binding of pyridine to chloroindiumtetraphenylporphyrin is a low-characteristic reaction. 相似文献
13.
The effects of cation solvation and the volume change (Delta V) of reaction on the equilibrium and the morphology change in the cation-exchange reactions of metal chalcogenide nanocrystals, CdE --> M(x)E(y) (E = S, Se, Te; M = Pd, Pt), were investigated. Since the solvation of cations is an important controllable factor determining the free energy of the reaction, the effect of varying cation solvation conditions on the equilibrium of the reaction was examined. A two-phase solvent environment, where the cations involved in the exchange reaction were preferentially solvated in different phases by using selective cation complexing molecules, was particularly efficient in increasing the thermodynamic driving force. The effect of Delta V of reaction on the morphology of the product nanocrystals was also investigated. Depending on the stress developed in the lattice during the reaction, product nanocrystals underwent varying degrees of morphological changes such as void formation and fragmentation in addition to the preservation of the original morphology of the reactant nanocrystals. The knowledge of the effect of ion solvation and Delta V of reaction on the equilibrium and product morphology provides a new strategy and useful guides to the application of cation-exchange reactions for the synthesis of a broader range of inorganic nanocrystals. 相似文献
14.
Effects of protonation on the thermodynamic properties of alkyl dimethylamine oxides 总被引:2,自引:0,他引:2
The effects of protonation on alkyldimethyl amine oxide micelles are reviewed, mainly with regard to dodecyl and tetradecyl homologs. The topics discussed are hydrogen ion titration properties, critical micelle concentration (CMC), area per surfactant and micelle aggregation number. A hydrogen bond hypothesis is proposed to interpret the several characteristic results associated with protonation: between two cationic species as well as between the non-ionic-cationic pair. The dipole-dipole interaction of the non-ionic micelle is discussed in relation to both: (a) the unusually high CMC values of the non-ionic micelles compared with other non-ionic surfactants with the same hydrocarbon chain; and (b) the reversal of the stability of the non-ionic and the cationic micelles at high ionic strengths. Two different approaches of the salting out effect on the ionic micelles are compared, the Chan-Mukerjee approach and ours, in relation to the non-linear Corrin-Harkins relation. The obtained salting out constants of the surfactants carrying a dodecyl chain decreased as the head group becomes more polar. Infrared and 13C-NMR spectra data are examined from the point of the specific interaction claimed by the hydrogen bond model. Mixed surfactant systems including amine oxides and the solid state phase behavior of amine oxides are both briefly reviewed. 相似文献
15.
Hong Zhang Zhenggang Wang Jiaren Dai 《Journal of Thermal Analysis and Calorimetry》1995,45(1-2):109-115
Correlations were determined between heat capacity and temperature and phase change enthalpy of Ba(OH)2·8H2O. The phase diagram and DSC curve of the binary system Na2CO3·10H2O?Na2HPO4·12H2O were determined The kinetics of the dehydrating reaction of Ba(OH)2·8H2O, Na2CO3·10H2O and Na2HPO4·12H2O were measured and theoretically analyzed by TG. 相似文献
16.
The overall rate constants of the NO reaction with chloroalkylperoxy radicals derived from the Cl-initiated oxidation of several atmospherically abundant alkenes-ethene, propene, 1-butene, 2-butene, 2-methylpropene, 1,3-butadiene, and isoprene (2-methyl-1,3-butadiene)-were determined for the first time via the turbulent flow technique and pseudo-first-order kinetics conditions with high-pressure chemical ionization mass spectrometry for the direct detection of chloroalkylperoxy radical reactants. The individual 100 Torr, 298 K rate constants for each monoalkene system were found to be identical within the 95% confidence interval associated with each separate measurement, whereas the corresponding rate constants for 1,3-butadiene and isoprene were both approximately 20% higher than the monoalkene mean value. Our previous study of the reaction of hydroxylalkylperoxy radicals (derived from the OH-initiated oxidation of alkenes) with NO yielded identical rate constants for all of the alkenes under study, with a rate constant value within the statistical uncertainty of the value determined here for the NO reaction of chloroalkylperoxy radicals derived from monoalkenes. Thus, the reaction of NO with chloroalkylperoxy radicals derived from dialkenes is found to be significantly faster than the NO reaction with either chloroalkylperoxy radicals derived from monoalkenes or hydroxyalkylperoxy radicals derived from either mono- or dialkenes. 相似文献
17.
Excess values of molar volumes, viscosities, molar enthalpies, Gibbs molar energies, surface tensions and molar diamagnetic susceptibilities were calculated at 25°C for then-butylamine+p-dioxane system. The observed deviations from the ideality were explained on the basis of intermolecular interactions. Van Laar's equations were the best in predicting activity coefficients for this system. 相似文献
18.
19.
Thermodynamic and equilibria properties of two vitamin B12 coenzyme analogues, i.e. 1-methyl-5-deoxy--d-(–)ribofuranosylcobalamin (RibCbl) and 1-methyl-5-deoxy-2,3-isopropylidene--d-(–)ribofuranosylcobal- amin (Rib*Cbl) were studied by u.v.-vis. spectroscopy. Their temperature-dependent equilibria between 6-coordinate base-on species and 5-coordinate unprotonated base-off species, and pH-dependent equilibria for the protonation and displacement of 5,6-dimethylbenzimidazole at 25°C have been examined. Values of H and S in neutral solution and at pH 4.00, and the axial base pKa were determined. Comparing the results with those for coenzyme B12 and other cobalamins, it has been found that H and S values for two ribosylcobalamins fall in the range of organocobalamins, but for RibCbl*, a ca. 1 unit difference in pKa values exists. The effect of the ribofuranose structure on the Co-N(dbzm) strength is considered. 相似文献
20.
Roman Dziembaj 《Journal of solid state chemistry》1978,26(2):159-165
Measurements of oxygen equilibrium pressure above the V2O5?x oxide system have been performed within the temperature range 575 to 615°C. The results have been used to determine the standard enthalpy and entropy in the reaction V6O13 + O2 = 3 V2O5. The thermodynamic properties of the V2O5?x system (at x < 1) cited in the literature have been discussed for all the equilibria postulated. 相似文献