Showing papers on "Reaction rate published in 1972"
TL;DR: In this article, a method of comparing the kinetics of isothermal solid-state reactions based on the classical equation for analysis of nucleation-and growth processes is described, where plots of In In (1-α) vs In (time), where α is the fraction reacted, are used to distinguish reaction mechanisms.
Abstract: A method of comparing the kinetics of isothermal solid-state reactions based on the classical equation for analysis of nucleation-and-growth processes is described. In this method, plots of In In (1-α) vs In (time), where α is the fraction reacted, are used to distinguish reaction mechanisms. Even nonintegral slopes obtained for values of the fraction reacted from 0.15 to 0.50 may indicate whether the reaction rate is diffusion- or phase-boundary-controlled. The problems of ascertaining zero time and self-cooling (or heating) of the reacting sample can be observed in the analysis but do not cause severe difficulties in interpretation, as they can for analyses based on reduced-time plots. The analysis is applied to the dehydroxylation of kaolinite and of brucite and the decomposition of BaCO3.
636 citations
TL;DR: Theoretical results based on the methods of Freeman and Garr & Marrone show that the stand-off distance and flow pattern of non-equilibrium dissociating flow of nitrogen over the front part of a blunt body can be correlated in terms of a single reaction rate parameter ω taking account of parameters describing the speed, density, dissociation and temperature of the free stream as discussed by the authors.
Abstract: Theoretical results based on the methods of Freeman and Garr & Marrone show that the stand-off distance and flow pattern of non-equilibrium dissociating flow of nitrogen over the front part of a blunt body can be correlated in terms of a single reaction rate parameter ω taking account of parameters describing the speed, density, dissociation and temperature of the free stream. The density pattern, which is sensitive to the reaction rate, consists of two distinct regions dominated by the effects of reaction and pressure respectively. The shape and size of these regions depend on Q. Experimental results obtained by optical interferometry in a free-piston shock tunnel confirm the theoretical results. A scale effect consistent with the induction time phenomenon suggested by Shui, Appleton & Keck modifies the theoretical results considerably in the case of small models.
204 citations
TL;DR: The intermediate is a charge transfer complex of reduced enzyme and keto acid and that it participates in catalysis, and is concluded that the pathway for acetate production includes the nonenzymatic reaction of these two substances.
190 citations
TL;DR: In this article, the reaction rates of pure calcite and pure dolomite with 100% phosphoric acid were investigated and it was shown that for mixtures the particle size range should be limited to minimize the cross-contamination of evolved CO2 which is later analyzed for δO18.
111 citations
TL;DR: In this article, the Fischer-Tropsch reaction over triply promoted iron catalyst was studied in a differential reactor at 240 °C, in the pressure range 10 to 20 bar with synthesis gases of H2CO ratio varying from 1 to 7.
107 citations
TL;DR: In this article, a three-dimensional, classical trajectory calculation is made of the collision dynamics of the reaction F+H2(v, J)→HF(v′, J′)+H by means of the London Eyring-Polanyi-Sato (LEPS) potential energy surface.
Abstract: A three‐dimensional, classical trajectory calculation is made of the collision dynamics of the reaction F+H2(v, J)→HF(v′, J′)+H by means of the London‐Eyring‐Polanyi‐Sato (LEPS) potential energy surface. Monte Carlo procedures are used to start each collision trajectory. A discussion is presented of the temperature dependence of the relative rates of formation of vibrationally excited hydrogen fluoride. By means of this calculation, it can be predicted that 71% of the mean fraction of available energy will become vibration in HF, 10.5% will become rotation in HF, and 18.5% will become translation in the product. The probability that direct chemical reaction between atomic fluorine and molecular hydrogen will lead to the formation of the product HF molecule in the ground vibrational state v′=0 was found to be zero. The ratio k(v′=3)/k(v′=2) appears to be independent of temperature and has a value of 0.49, which is in excellent agreement with available experimental data. The ratio k(v′=2)/k(v′=1) has a slig...
98 citations
TL;DR: In this paper, the effects of fractional monolayers of carbon monoxide, reduced carbon dioxide and arsenic on the rates of hydrogen-oxidation and evolution were examined on unpoisoned platinum sites in 2 N H2SO4 at 25°C.
91 citations
TL;DR: In this paper, the authors investigated the reaction of D2+12O2→D2O occurring on a (111) Pt surface using modulated molecular beam techniques and derived a reaction rate proportional to PD 2 2.0 PO 2 0.8 exp[−3.6 (kcal/mole) / kTD 2]
Abstract: The reaction D2+12O2→D2O occurring on a (111) Pt surface has been investigated using modulated molecular beam techniques. With a molecular beam of D2 and a (111) Pt surface immersed in an O2 ambient, the production of D2O was studied as a function of D2 flux and temperature, O2 pressure, Pt temperature and the angle of incidence of the D2 beam. From these data the rate of production of D2O can be expressed by a reaction rate proportional to PD 2 2.0 PO 2 0.8 exp[−3.6 (kcal/mole) / kTD 2] exp[−12 (kcal/mole) / kTPt] in the pressure and temperature regime PD 2 ∼ 10 −7 torr, PO 2 ∼ 10 −5 torr, TD 2 ∼ 1200°K, and TPt ∼ 700°K. Further, a reaction mechanism which is consistent with this rate expression and also with the observed angular dependence is presented.
84 citations
IBM1
TL;DR: In this article, a kinetic model for the reaction between silicon and oxygen at the interface is presented to account for the experimental data, and two parallel, competing reactions are postulated to occur.
Abstract: The thermally activated growth of oxide on silicon as a function of time obeys a linear‐parabolic relationship, the linear part of which stems from interface limited reactions. In Part I of this paper, it has been reported that this linear part cannot result from a single rate‐limiting reaction step, because the order of the over‐all reaction rate differs for different substrate orientations at a fixed temperature and varies for a given orientation as a function of temperature. A kinetic model for the reaction between silicon and oxygen at the interface is now presented to account for the experimental data . Two parallel, competing reactions are postulated to occur. In the first of these, molecular oxygen reacts directly with silicon to form silicon dioxide and atomic oxygen; the second reaction involves the dissociation of O2. The atomic oxygen thus formed, may either react with silicon or recombine to molecular oxygen. An analysis of the data shows that a difference in the activation energies (i.e., 1.91 vs. 0.58 eV) associated with these competing reaction steps is responsible for the shift in their relative importance as a function of temperature.
81 citations
TL;DR: In this paper, an analytical solution for the dispersion of a solute in a liquid flowing between two parallel plates in the presence of an irreversible first-order chemical reaction is presented.
Abstract: The paper presents an analytical solution for the dispersion of a solute in a liquid flowing between two parallel plates in the presence of an irreversible first-order chemical reaction. The effects of both homogeneous and heterogeneous reactions on the dispersion are studied under isothermal conditions. It is found that for homogeneous reaction in the bulk of the liquid, the effective Taylor diffusion coefficient decreases with increase in the reaction rate constant. Further for heterogeneous reaction at the catalytic walls, Taylor diffusion coefficient is also found to decrease with increase in the wall catalytic parameter for fixed reaction rate constant corresponding to the bulk reaction.
79 citations
TL;DR: An effectiveness factor, the ratio of the actual reaction rate to that which would obtain in the absence of diffusive and electrostatic effects, is defined and shown to be a function of an electrostatic parameter, the Michaelis constant, and the ratios of the maximum reaction rate and the maximum transfer rate.
TL;DR: In this paper, a mechanism involving the oxidation and reduction of the solid is presented for carbon monoxide oxidation on cerium dioxide, and expressions for the reaction rate and the electrical conductivity of the catalyst are derived from this mechanism.
TL;DR: Two roles are proposed for the metal ion in this reaction: activation of the enzyme to a form which binds substrate, and formation of substrate by complexing with PPi.
TL;DR: The reaction between nickel and argon atmospheres containing 10% sulphurdioxide has been studied over the temperature range 475-900° in this article, where the reaction kinetics are complex and do not conform to any single simple rate law over the whole course of the reaction period.
TL;DR: In this article, the authors studied the kinetics of the reactions between Na2SO4 (X) and V2O5 (Y) and showed that the rate of the reaction depends both on the temperature (600-1300°C) and the molar ratios of X:Y.
TL;DR: Kinetic studies of the hydrolysis of N‐benzoyl‐L‐arginine ethylester as a model reaction indicated that the reaction was kinetically controlled in reactors with surface bound trypsin and the kinetic parameters were evaluated by conventional methods.
Abstract: Tubes with immobilized enzymes on the inner wall, called open tubular heterogeneous enzyme reactors, were prepared by binding enzymes either directly to the tube inside surface or to a layer of a porous matrix attached to the inner wall. Kinetic studies of the hydrolysis of N-benzoyl-L-arginine ethylester as a model reaction indicated that the reaction was kinetically controlled in reactors with surface bound trypsin and the kinetic parameters were evaluated by conventional methods. On the other hand, substrate diffusion in both the porous matrix and the bulk substrate solution strongly affected the rate of reaction in porous layer trypsin reactors. The highest overall rates of reaction were obtained when the reaction was bulk diffusion controlled and the measured rates were in agreement with those calculated from expressions derived from heat transfer theory. The design of reactors for the limiting cases of kinetic and bulk diffusion controlled reaction as well as a method for the determination of substrate diffusivity are outlined.
TL;DR: In this paper, the structure of a reacting surface in a turbulent flow involving contiguous volumes of fluid with one reactant present and the other absent is studied by an idealized model, and the analysis provides estimates of the several length scales involved and distributions of the reactants and product in the neighborhood of such a surface assuming that the diffusivity of species is much less than that of momentum.
Abstract: The structure of a reacting surface in a turbulent flow involving contiguous volumes of fluid with one reactant present and the other absent is studied by an idealized model. The analysis provides estimates of the several length scales involved and distributions of the reactants and product in the neighborhood of such a surface assuming that the diffusivity of species is much less than that of momentum. The analysis also indicates that the coupled dissipation terms arising in Part I must be considered negligibly small in the limit of infinite reaction rates. The results of an experiment involving the turbulent mixing of weak-acid and weak-base solutions are discussed and are shown to provide qualitative support for the picture of reacting surfaces evolving from this study. Salt produced by the reaction was detected using a single electrode conductivity probe with effective diameter about 5 microns.
TL;DR: In this paper, the effect of temperature on the reaction rate of grouped species which are consumed by parallel nth-order irreversible reactions is investigated, and it is shown that when the activation energies of the individual reacting species are aboput equal the temperature effect can be described by an Arrhenius expression.
Abstract: The effect of temperature on the reaction rate of grouped species which are consumed by parallel nth order irreversible reactions is investigated. It is shown that when the activation energies of the individual reacting species is aboput equal the temperature effect can be described by an Arrhenius expression. However, when the activation energies of the various reactions are widely spread the Arrhenius dependence may not be adequate unless one assumes that the activation energy of the lump may be temperature and conversion dependent. Unter these conditions the Arrhenius temperature dependence is at best a rough approximation and it is very important to define exactly the experimental method of determining the activation energy. Widely different activation energies for the pseudocomponent may be obtained from different experimental techniques which yield the same value for a single reactant.
TL;DR: In this paper, the reaction rates between sulfide and oxygen in the presence of extraneous substances were studied and it was concluded that the treatment of sulfide-bearing industrial wastewater as well as the oxygenation in natural environment can be greatly accelerated through proper use of catalysts.
Abstract: Reaction rates between sulfide and oxygen in the presence of extraneous substances were studied. Divalent metal ions and organic substances such as phenols and aldehydes were found to exert accelerating effects. Compounds containing a basic nitrogen with a free electron pair were found to be chain-breakers and to inhibit the reaction. Four types of influence were observed in this study: (1) A shortening or lengthening of the induction period; (2) a change in the stoichiometry of the reaction; (3) a change in reaction rate; and (4) an induced oxidation of the added organic material. It is concluded that the treatment of sulfide-bearing industrial wastewater as well as the oxygenation of sulfide in natural environment can be greatly accelerated through proper use of catalysts.
TL;DR: In this paper, the O2+−H2O reaction sequence, the hydration of NO+, and new measurements of charge exchange and ion-atom interchange for E-region ions are presented.
Abstract: Results are presented for recent measurements of reaction rates using the NOAA flowing afterglow systems. These include the O2+−H2O reaction sequence, the hydration of NO+, and new measurements of charge exchange and ion-atom interchange for E-region ions.
TL;DR: The kinetics of hydrogen-deuterium exchange in hen egg-white lysozyme (muramidase) has been followed in aqueous solutions of various pH values and in solutions with various concentrations of lithium chloride, by an infrared absorption measurement.
TL;DR: In this paper, the reaction of NO2− and NO3− with HCl and HBr was carried out in a flowing afterglow system at room temperature and the reaction rate constants were measured.
Abstract: Reactions of NO2− and NO3− with HCl and HBr were carried out in a flowing afterglow system at room temperature and the reaction rate constants were measured. The reaction NO3−+HBr→ Br−+HNO3 is found to be nearly thermoneutral. The results lead to these values of electron affinities: E.A. (NO2)< 2.6 eV, E.A.(NO3)=3.9± 0.2 eV. In addition, rate constants for the reactions of NO− and O2− with HCl are reported. A number of cluster ions were observed: NO3−(HCl)1,2, NO3−(HNO3)1,2, NO3−· HNO3(HCl)1,2, and Br− (HNO3)1,2.
TL;DR: A computer simulation of a pulsed HF laser pumped by the H( 2) + F(2) chain reaction is presented, finding that laser performance is most sensitive to the relative rates of the vibrational-translational and pumping reactions.
Abstract: A computer simulation of a pulsed HF laser pumped by the H2 + F2 chain reaction is presented. A chemical kinetic model encompassing sixty-eight reactions is used to approximate the reacting mixture contained within an optical cavity. For each vibrational level, a Boltzmann distribution for the rotational levels is assumed, with lasing on the vibrational band at line center of the transition having maximum gain. An analysis of cavity and chemical mechanisms yields a simple relationship between the pumping and depletion rates of the vibrational levels. This relationship is used to make a comprehensive study of the effects of cavity and chemical parameters on the laser pulse. The effect of changes in uncertain chemical reaction rate coefficients is assessed. A competition exists between vibration–translation deactivation reactions and stimulated emission. Laser performance is most sensitive to the relative rates of the vibrational–translational and pumping reactions. In addition, the effect of the photon flux on the chemical mechanisms is significant.
TL;DR: In this paper, a quadratic dependence of thionine reformation on excitation intensity at high oxygen concentration was observed, indicating a reaction between two photoproducts.
Abstract: — The photooxygenation of allylthiourea (ATU) sensitized by thionine does not occur according to the singlet oxygen mechanism but rather proceeds via the formation of radicals. In oxygen-free solution the primary process is a redox reaction between the thionine triplet and ATU where a semithionine- and an ATU-radical are formed. In further reaction steps the leuco form of the dye is finally produced (reductive photobleaching; D
R mechanism after Koizumi). The primary process in an oxygen-containing aqueous solution is the same, since at high concentrations of ATU (0·2M) the amount of semithionine formed by a photolytic flash, as well as the time course of disappearance of semithionine, does not depend on the oxygen content of the solution.
The reformation of thionine following flash photolysis has been investigated with regard to oxygen concentration and pH dependence. Two different excitation intensities were used. A quadratic dependence of thionine reformation on excitation intensity at high oxygen concentration was observed, indicating a reaction between two photoproducts.
The dependence of the reaction rate of semithionine on the ionic strength has been investigated. These experiments show that the reaction partner of semithionine carries a charge of + 1 in oxygen-free as well as in oxygen-saturated solution.
TL;DR: In this paper, it was shown that a subset of the thermodynamic states remains invariant to both the chemical reactions and the control actions, and that the reduced reaction matrix and the mean residence time still determine the response modes entirely.
TL;DR: In this article, it was observed that the reaction product had little mechanical strength and readily disintegrated into a molecular-scale powder and was identified as γ-Al2O3 which even after heating for 48 h at 750° C was still of the order of 60 to 70 A in average particle size.
Abstract: Aluminium, in its normal passivated state, does not react with mercury, i.e., it is not attacked and does not wet or readily dissolve. When the passivating surface layer is removed from high-purity aluminium, the metal can be easily wetted by mercury and upon exposure to air a spontaneous and rapid growth of a fibrous or ribbon-like product emanates from the wetted surfaces. In this work it was observed that the reaction product had little mechanical strength and readily disintegrated into a molecular-scale powder. It was identified as γ-Al2O3 which even after heating for 48 h at 750° C was still of the order of 60 to 70 A in average particle size. By consideration of the Al-Hg phase diagram, thermodynamic data, and further experimental observations, a mechanism for the phenomenon has been proposed. The probably unique situation which exists at room-temperature in the Al-Hg system enables a spontaneous reaction to take place between the aluminium dissolved in the wetting mercury film and the water vapour and oxygen present in the atmosphere. The influences of several variables on the reaction product morphology and relative reaction rate were investigated. Also, other mercury-metal systems were investigated for possible similar reactions.
TL;DR: In this article, the effect of the addition of an inert liquid into a gas-phase reaction occurring on a solid catalyst was studied using the isomerization of cyclopropane to propylene on a sukuca-alumina catalyst as the model reaction and one of three hydrocarbon solvents as the liquid.
Abstract: The effect of the addition of an inert liquid into a gas-phase reaction occurring on a solid catalyst was studied using the isomerization of cyclopropane to propylene on a sukuca-alumina catalyst as the model reaction and one of three hydrocarbon solvents as the liquid. With a nonadsording liquid the intrinsic reaction rate constant is the same in both the gas and the gas-liquid systems but adsorption of impurities from the liquid or adsorption of the liquid itself can have an enormous retarding effect on the reaction rate. Even i the absece of these effects the addition of a liquid phase decreases the percet conversion and increses the likelihood of occurrence of mass transfer limitations.
TL;DR: In this article, an experimental study of the reaction rate for SO 2 oxidation on a commercial V 2 O 5 catalyst is presented, and the results show that most rate expressions are adequate only in a narrow temperature and composition range and that probably no single rate expression can be applied in the whole range of industrial operating conditions.