Showing papers on "Chemical kinetics published in 1983"
TL;DR: The rate of oxidation of ferrous iron in a seasonally anoxic lake was measured on 39 occasions with respect to both depth and time as discussed by the authors, and the data were consistent with the simple rate law for homogeneous chemical kinetics previously established for synthetic solutions.
317 citations
TL;DR: In this article, the specific activity for NO reduction was found to be sensitive to the nature of the catalyst pre-treatment, and the rate-limiting step in this model was assumed to be the dissociation of chemisorbed NO.
263 citations
TL;DR: In this article, the reduction of NO by carbonaceous solid has been studied in a packed bed reactor, and the reaction rate per unit total surface area is found to be first order in NO, to have an apparent activation energy of 44 kcal/mole for temperatures higher than 873K, enhanced by the presence of CO, and to vary by approximately an order of magnitude between graphite and coal chars.
231 citations
TL;DR: In this article, an experimental study of the reaction rate between monodisperse sulfuric acid aerosols and ammonia gas is described, where reaction time was 5.0 +/- 0.5 s, ammonia concentrations ranged from 13 to 63 ppb, and particle sizes ranged from 0.03 to 0.2 µm.
Abstract: An experimental study of the reaction rate between monodisperse sulfuric acid aerosols and ammonia gas is described. Reactions took place in a laminar flow reactor at 24/sup 0/C and 6% relative humidity, and reaction products were sampled from the core of the flow so that reaction times were well defined. For the data reported here, the reaction time was 5.0 +/- 0.5 s, ammonia concentrations ranged from 13 to 63 ppb, and particle sizes ranged from 0.03 to 0.2 ..mu..m. The extent of reaction was determined by comparing the hygroscopic and deliquescent properties of the product aerosols with known properties of aerosols consisting of internal mixtures of sulfuric acid and ammonium sulfate. It was found that the average fraction of ammonia-aerosol collisions that resulted in chemical reaction during neutralization decreased from 0.40 +/- 0.10 for 0.058-..mu..m particles to 0.18 +/- 0.03 for 0.10-..mu..m particles. Differential mobility analyzers were used for generating the monodisperse aerosols and also for measuring the hygroscopic and deliquescent properties of the product aerosols.
129 citations
TL;DR: In this paper, the reaction of N2O5 with water vapor, a potentially important nighttime loss reaction for NOx and formation pathway for nitric acid, has been investigated at 298 ± 1 K in two environmental chambers of 3800 and 5800 L volume.
Abstract: The reaction of N2O5 with water vapor, a potentially important nighttime loss reaction for NOx and formation pathway for nitric acid, has been investigated at 298 ± 1 K in two environmental chambers of 3800 and 5800 L volume. From the N2O5 decay rates as a function of water vapor concentration, an upper limit to the N2O5 + H2O rate constant of less than 2.4 × 10−21 cm³ molecule−1 s−1 is derived. However, while gas phase nitric acid was observed to be a major product, its yield, especially at low water vapor concentrations, was significantly lower than the value of 2 expected, indicating that the overall reaction in these chambers involved both homogeneous and heterogeneous components. After allowing for the contribution of the heterogeneous reaction, an estimate of the gas phase homogeneous rate constant for N2O5 + H2O of 1.3 × 10−21 cm³ molecule−1 s−1 was obtained. While this value must still be regarded as an upper limit to the homogeneous rate constant, it is a factor of 10 lower than the only directly measured upper limit reported previously.
108 citations
TL;DR: In this paper, the reaction kinetics for the leaching of MnO2 by sulfur dioxide have been studied using studied using monosize particles at dilute solid phase concentrations in a stirred reactor to determine the important chemical factors which govern the kinetic response of the system.
94 citations
TL;DR: In this article, an analysis of diffusion-influenced surface reactions using models similar to those used in solution kinetics is given, and it is shown that a pure two-dimensional model of surface reactions yields no steady state rate constant.
Abstract: An analysis is given of diffusion‐influenced surface reactions using models similar to those used in solution kinetics. It is shown that a pure two‐dimensional model of surface reactions yields no steady state rate constant. By incorporation of adsorption and desorption processes the deficiencies in the two‐dimensional results are eliminated. Expressions are derived for diffusion‐controlled and diffusion‐influenced rate constants for surface reactions. Expressions are also derived for the activation energies of these surface reactions. It is shown that the activation energy for diffusion‐controlled reactions will approximately be given by the activation energy for surface diffusion. Bounding expressions are developed for the activation energy for diffusion‐influenced reactions. Comparisons are made betweeen Langmuir–Hinshelwood and Eley–Rideal mechanisms, and it is found that Langmuir–Hinshelwood mechanisms should be more important than Eley–Rideal processes for many surface reactions.
82 citations
TL;DR: In this article, an experimental investigation in a conventional static apparatus of the oxidation of equimolecular methyl tert-butyl ether (MTBE)-oxygen mixtures has shown that MTBE oxidizes far less readily than alkanes like neopentane or 2,2-dimethylbutane.
79 citations
TL;DR: In this article, the rate constants for hydrogen-deuterium exchange reactions between HO/sup -/ and DO/sup-/ and a series of weakly acidic neutrals, both organic and inorganic, have been measured in the gas phase by using the selected ion flow tube (SIFT) technique.
Abstract: Rate constants for hydrogen-deuterium exchange reactions between HO/sup -/ and DO/sup -/ and a series of weakly acidic neutrals, both organic and inorganic, have been measured in the gas phase by using the selected ion flow tube (SIFT) technique. The reaction efficiencies are discussed in terms of the initial ion-dipole complex energies, the relative acidities of the neutrals, and the change in solvation energy accompanying proton transfer; the effect of these energies on transition-state properties profoundly influences the outcome of the reactions. Exchange occurs rapidly between hydroxide and most aromatic and vinyl compounds but is relatively inefficient for hydrogen. The efficiency for exchange with ammonia is intermediate. Ethylene, dimethyl ether, and methane do not exhibit exchange.
77 citations
TL;DR: The solid state reaction between silicon carbide and a model superalloy consisting of 70 at.pct Ni, 20 at. pct Cr, and 10 at pct Al was studied between 700 °C and 1150 °C for times ranging from “0” hours to 330 hours as discussed by the authors.
Abstract: The solid state reaction between silicon carbide and a model superalloy consisting of 70 at. pct Ni, 20 at. pct Cr, and 10 at. pct Al was studied between 700 °C and 1150 °C for times ranging from “0” hours to 330 hours. Reaction couples consisting of SiC/Ni, SiC/Cr, and SiC/NiCr were also studied. The reactions were carried out in air with the materials, in the shape of discs, maintained in contact under a pressure of 7 MPa. A reaction was detected with SiC and the model alloy at all temperatures studied, and the reaction was diffusion controlled with an activation energy of 184 kJ/mole. In the ceramic the reaction was dominated by the diffusion of Ni into the ceramic forming a banded structure consisting of alternating layers of δ-Ni2Si and a two phase mixture of graphite and δ. On the metal side, the reaction was very dependent on the presence of alloying elements, with pure Ni reacting to the greatest extent, followed by the binary NiCr alloy, and finally by NiCrAl. The growth and presence of the phases detected in these reactions is consistent with phase equilibria concepts.
75 citations
TL;DR: In this article, a laser-based chemical kinetics technique has been demonstrated in studies of the reaction of OH with C2H4, which is dominated by electrophilic addition of OH to the double bond at low temperatures, and by increasingly rapid decomposition of the thermalized adduct HOC 2H4 back to reactants as the temperature is raised.
TL;DR: In this article, the authors investigated the kinetics of well-activated LaNi5 using a mass flowmeter under constant hydrogen pressure and showed that the overall rate is controlled by the rate of reaction at the interface which can be expressed as ======k ln(PPet=1 − (1−X)1/3
Abstract: The kinetics of well-activated LaNi5 were investigated using a mass flowmeter under constant hydrogen pressure. The overall rate is controlled by the rate of reaction at the interface which can be expressed as
k ln(PPet=1 − (1−X)1/3
where P is the hydrogen pressure and Pe is the equilibrium plateau pressure.
TL;DR: In this article, the reaction of hydroxyl radicals with hydrogen in aqueous solutions has been studied in the temperature range 20 to 230/sup 0/C. The rate constant of the reaction was determined either by competition kinetics, using Cu/sup 2 +/ as the competitor, or through the measurement of the formation rate of O/sub 2//sup -/ n aqous solutions of oxygen and hydrogen.
Abstract: The reaction of hydroxyl radicals with hydrogen in aqueous solutions has been studied in the temperature range 20 to 230/sup 0/C. The rate constant of the reaction was determined either by competition kinetics, using Cu/sup 2 +/ as the competitor, or through the measurement of the formation rate of O/sub 2//sup -/ n aqueous solutions of oxygen and hydrogen. The rate constants at 20 and 230/sup 0/C are (3.4 +- 0.3) x 10/sup 7/ and (7.7 +- 1.5) x 10/sup 8/ dm/sup 3/ mol/sup -1/ s/sup -1/, respectively. The activation energy of the reaction is 19 kJ mol/sup -1/ (4.6 kcal mol/sup -1/).
TL;DR: In this article, the kinetics of hydrogen evolution from colloidal Pt catalyst reacting with methyl viologen radicals was studied in detail and the results were compared with those in previous studies of the same reaction catalyzed by gold sols.
Abstract: The kinetics of hydrogen evolution from colloidal Pt catalyst reacting with methyl viologen radicals was studied in detail and the results are compared with those in previous studies of the same reaction catalyzed by gold sols. The major difference between the two catalysts is in the rate of the proton discharge step. In the Pt-catalyzed reaction this step follows immediately the electron transfer reaction from the reductant to the particle. The Pt particle may therefore be viewed as a storage pool of hydrogen atoms rather than electrons. The dependence of the rate on catalyst concentration in Pt, as well as in Au, is second order in the catalyst and the possibility of a particle-particle reaction is further examined.
TL;DR: Silica-supported triosmium carbonyl clusters were prepared by the reaction of [Os3(CO)12] with -OH groups of the silica surface as mentioned in this paper.
TL;DR: In this article, two kinetic regimes were observed in the decomposition of NH3 over nickel wires at temperatures between 750 and 1350K and NH3 pressures between 5.3 and 133 Pa.
TL;DR: In this paper, the role of ion-molecule reactions in the conversion of N2O5 to HNO3 was investigated, and the reaction rate constant measurements were made in a flowing afterglow apparatus for hydrated H3O+, H+(CH3CN)m (m = 1, 2, 3).
TL;DR: In this article, the rate of CO hydrogenation into methane over Ni SiO 2 catalysts is shown to vary in a complex way with temperature and pressure, and the true activation energy, E0, calculated from the Temkin relation, corresponds to that of the hydrogenation of carbon deposited on the surface from the CO dissociation reaction.
TL;DR: In this article, the structure of a steady, planar premixed flame in a slowly expanding gas flow is analyzed and the reaction kinetics are represented by a mechanism consisting of a chain branching reaction and a chain breaking reaction.
Abstract: The structure of a steady, planar. premixed flame in a slowly expanding gas flow is analyzed. The reaction kinetics are represented by a mechanism consisting of a chain branching reaction and a chain breaking reaction. An asymptotic analysis is performed in the limit of a large value for the activation energy of the chain branching reaction, with the activation energy for the chain breaking reaction presumed to be zero. The analysis is valid for cases where the mass fraction of the intermediate species is of order unity, An analytical expression is obtained for the change of the mass burning rate with the Karlovitz number, the parameter characterizing flame stretch. This expression shows the role of differential diffusion of heat and the reactant, of differential diffusion of reactant and intermediate species and of enhanced diffusion of intermediates on flame propagation. It is seen that these three different effects may cancel each other. Depending on the parameter range the mass burning rate m...
TL;DR: In this article, the effect of mixing on chemical reactions is analyzed by means of a model which treats simultaneously the complex interactions of mechanical mix diffusion and reaction, and a criterion is established for limits of reaction control of bimolecular reactions by mixing, including diffusion, and by chemical kinetics in terms of a single dimensionless group φ kC B 0 S 2 / D A.
TL;DR: In this paper, the reaction mechanisms with Li of various metal oxides, sulfides and a selenide in nonaqueous electrolyte have been studied by the galvanostatic method, X-ray diffraction analysis, and ion-microanalysis.
TL;DR: In this article, a wavefront analysis of the dependence of the microkinetics of the water-gas shift reaction on the oxidation state of a CuOZnO industrial catalyst is reported.
TL;DR: In this paper, the gas phase reaction of D with HCl was studied at room temperature by the method of flash photolysis, with resonance fluorescence detection of D, H, and Cl atoms.
Abstract: The gas phase reaction of D with HCl was studied at room temperature by the method of flash photolysis, with resonance fluorescence detection of D, H, and Cl atoms. The D and Cl atoms were observed to decay exponentially, whereas no H atom signal from the exchange reaction was detectable. From the calibrated sensitivity of the H atom detector, an upper limit of 0.002 was set for the ratio of rate constants for the exchange vs abstraction channels.
01 Feb 1983
TL;DR: In this paper, a chemical kinetic reaction mechanism for the oxidation of silane/hydrogen mixtures is presented and discussed, and the results revealed that substantial reduction in ignition delay times is obtained when silane is added to hydrogen.
Abstract: A chemical kinetic reaction mechanism for the oxidation of silane/hydrogen mixtures is presented and discussed. Shock-tube ignition delay time data were used to evaluate and refine the mechanism. Good agreement between experimental results and the results predicted by the mechanism was obtained by adjusting the rate coefficient for the reaction SiH3 + O2 yields SiH2O + OH. The reaction mechanism was used to theoretically investigate the ignition characteristics of silane/hydrogen mixtures. The results revealed that over the entire range of temperature examined (800 K to 1200 K), substantial reduction in ignition delay times is obtained when silane is added to hydrogen.
TL;DR: In this article, the authors investigated the mass transfer rate of Zn(II), Co(II) and Ni(II ) between aqueous nitrate solutions and n-dodecane solutions of the organic soluble ligand HDEHP using a forced convection, constant interfacial area stirred cell and concluded that if interfacial chemical reactions are rate controlling, rate constants of interfacial complex formation reactions independent of the nature of the cation are obtained.
Abstract: The mass transfer rate of Zn(II), Co(II) and Ni(II) between aqueous nitrate solutions and n-dodecane solutions of the organic soluble ligand HDEHP has been investigated using a forced convection, constant interfacial area stirred cell. The distribution ratios necessary to evaluate the kinetic experiments have been determined and the equilibrium constants which describe the heterogeneous complex formation reaction between Zn2+, Co2+, Ni2+ and HDEHP have been evaluated. The results have been interpreted according to two limiting models: 1) the mass transfer rate is controlled by slow reversible interfacial reactions, 2) the mass transfer is controlled by interfacial film diffusion. Both models are adequate to Interpret the experimental data. The conclusion Is reached that, if interfacial chemical reactions are rate controlling, rate constants of interfacial complex formation reactions independent of the nature of the cation are obtained. This result supports a reaction mechanism which is rate contr...
TL;DR: In this paper, a reversible charge-state-dependent defect reaction in 1-MeV-electron was observed by capacitance transient spectroscopy and thermally stimulated capacitance, characterized by metastable defect configurations at $T\ensuremath{\lesssim}160$ K.
Abstract: We report the observation of a reversible charge-state---dependent defect reaction in 1- MeV-electron---irradiated $n$-type InP. The reaction, observed by capacitance transient spectroscopy and thermally stimulated capacitance, is characterized by metastable defect configurations at $T\ensuremath{\lesssim}160$ K. The electronic properties of the two configurations, together with the reaction kinetics, provide evidence regarding the nature of the defects involved. The phenomenon can be described by a model involving the interaction of a shallow donor with an intrinsic defect or defect complex. The defect charge state controls an electrostatically driven pairing-dissociation reaction which results in changes in the observed defect electronic properties.