Determination of rate constants for nonequilibrium reactions in gases with participation of electrons from ballistic experiments

Investigations on determination of the rate constants for reactions in nonequilibrium processes from ballistic experiments are reviewed. We obtained and give here the constants fro dissociative recombination in air, nitrogen, argon, krypton, and xenon and also the constants for ternary recombination of Al⁺ and the attachment constants for aluminum oxides. Institute of Mechanics of Moscow State University, Moscow 119899. Translated from Fizika Goreniya i Vzryva, Vol. 33, No. 2, pp. 39–51, March–April, 1997     

A droplet-based high-throughput tubular platform to extract rate constants of slow chemical reactions

A high-throughput tubular millifluidic platform for performing slow kinetics measurements occurring in liquid phase, using minute amounts of reactant is described. The method consists of generating periodic trains of monodisperse droplets in a capillary tube and using these droplets as micro-reactors. In contrast to microfluidic lab-on chip devices, limited to fast kinetics measurements, this setup permits to extract kinetic rate constants of slow reactions at very low cost without requiring any use of soft lithography or glass etching technique for its design, nor miniaturization of analytical tools. It therefore appears very well suited for laboratories and industrial research and development centers.     

Evaluation of basis sets and theoretical methods for estimating rate constants of mercury oxidation reactions involving chlorine

The occurrence of elemental mercury in flue gases from coal combustion is a problem of current environmental concern. Oxidized mercury species can be effectively removed from the flue gases by chemical scrubbers. However, the detailed mechanism by which oxidation occurs remains unclear. Theoretical rate constants are calculated for mercury oxidation by atomic chlorine. The potential energy surface is determined using standard quantum chemical methods with relativistic effects included via the use of an effective core potential (ECP). Experimental thermodynamic and kinetic data are employed to assess the accuracy of these calculations. Results show that the QCISD method with the 1992 basis set of Stevens et al. gives good agreement with experiment, suggesting that this combination may be useful for other mercury–chlorine chemical systems.     

The galvanostatic single-pulse and the coulostatic impulse methods for the determination of the rate constants of electrode reactions

The information on kinetic parameters of electrode reactions obtained with the galvanostatic single-step, the coulostatic impulse and the faradaic impedance methods is examined as a function of the applied electrolysis time and the ac frequency. A time and a frequency condition is given for which the information on kinetics obtainable with these methods is maximal. In the usual approach to the single-step and the coulostatic impulse methods these optimal conditions cannot be met. We present here a new procedure with which the experimental data measured with both methods can be interpreted exactly over the whole region of the η/t curve by means of numerical tables. The application of these tables enhances the limit of the applicability of the single-step method by a factor of 3 and that of the coulostatic impulse method by a factor of 100. The methods are applied to the Cd²⁺/Cd (Hg)-electrode in 1 M NaClO₄ and the Hg₂²⁺/ Hg electrode in 1 M HClO₄.     

Estimation of kinetic constants for reactions in thin films

The problem of synthesizing a product in thin films taking into account a finite reaction rate at the phase boundaries is considered. Formulas are derived that determine the dynamics of synthesis in the diffusive regime and in the regime controlled by the boundary kinetics. Based on these formulas, procedures are proposed for estimating the parameters of the boundary kinetics.     

Liquid-chromatographic determination of rate constants for the cellulose-dimethyloldihydroxyethyleneurea reaction

Rates of the MgCl₂-catalyzed reaction between cellulose and 4,5-dihydroxy-1,3-bis(hydroxymethyl)-2-imidazolidinone were measured at 70, 90, and 110°C. The rate constants were determined by curing the resin for various times, extracting the unreacted resin, and determining its concentration by liquid chromatography. The energy of activation was calculated from the rate data. This work confirms the pseudo-first-order behavior of this reaction.     

Determination of the rate constants for a CECE reduction mechanism

We have made a generalized treatment of first-order kinetic processes in dc polarography, obtaining approximate analytic expressions, applicable to any conditions. This treatment is applied to the electrochemical reduction of O-nitrophenol, which undergoes a CECE mechanism in which both chemical stages influence the process simultaneously. All the rate constants involved in the process have been calculated.     

Estimation of rate constants during polypropylene autoxidation

Recently, Chien and Boss calculated rate constants for the autoxidation of isotactic polypropylene based upon a postulated relatively simple scheme. Electron spin resonance, volumetric, and chemical techniques were employed. It behooved the authors of this paper to demonstrate that similar values of these rate constants could also be calculated from a more general scheme. From this general scheme, expressions were derived which involved the rate constants of interest and other constants which had been previously calculated from experimental data based upon the use of infrared absorption techniques. The values of our calculated rate constants at various temperatures agreed well with those reported by Chien and Boss where comparison was possible.     

Prediction of adsorption rate constants of activated carbon for various vapors

In the past decade, a theoretical calculation of the adsorption properties of activated carbon has successfully been used to predict the adsorption capacity for untested vapors after initial characterization of the carbon with a reference vapor. However, using this theoretical approach, it has not been possible to predict the second fundamental property of carbons, namely its adsorption rate constant, and therefore only a family of curves for adsorption performance could be calculated. A new extension of the present theory is proposed which would permit prediction of the adsorption rate constant of vapors, after initial characterization of the carbon with a reference vapor, so that a curve of adsorption performance can be calculated for any vapor needed.     

The effects of reactant starvation and mass transfer in the rate measurement of fluid-solid reactions with small equilibrium constants

The purpose of this article is to analyze critically and quantitatively the effect of fluid reactant supply rates and mass transfer on the measurement of the rates of fluid-solid reactions, particularly those with small equilibrium constants. It is shown through a mathematical analysis that the measurement of the intrinsic kinetics of a reaction with a small equilibrium constant (a positive standard free energy of reaction) requires much larger rates of fluid reactant supply and mass transfer rates than that of a reaction with a large equilibrium constant. The overall reaction rate of the former also tends to be slow. Furthermore, the apparent activation energy of such a reaction approaches the standard enthalpy of reaction (ΔH⁰), rather than the true activation energy of the chemical reaction.     

甲基丙烯酸-3-三甲氧基硅丙酯的水解-缩合反应速率常数

在甲基丙烯酸-3-三甲氧基硅丙酯（MPS）和苯乙烯的乳液共聚合反应中,MPS与水接触时其SiOR基团会发生水解缩合反应,其反应速率对乳液体系的稳定有很大的影响,而且所得产物的杂化结构也由SiOR基团的水解缩合反应速率决定.通过²⁹Si核磁共振谱,测定了不同pH值下MPS的水解-缩合速率常数.发现MPS的水解速率常数在pH=7时最小,无论是在酸性条件还是碱性条件都使其迅速增大.而MPS的缩合速率常数则在pH=4时达到最小,而在相对较高pH值和更低的pH值时,其缩合速率常数也都迅速增大.并得到了不同pH值时水解-缩合速率常数估算式.为进一步研究MPS乳液聚合的过程机理、反应过程动力学模型的求解以及通过模型对反应结果的预测提供了依据和基础数据.     

Kinetic rate constants determined by a digital computer

The difficulty of determining rate constants for complex reactions has been overcome with the development of a general digital computer program that can determine up to 10 rate constants in any reaction scheme which can contain as many as 10 components. A given reaction to which the experimental data are to be fit is described to the computer in a short one-step integration subprogram, which solves the differential equations representing the scheme. Only this subprogram needs to be rewritten to change the reaction scheme. Special features of the program and length of calculations are discussed. A copper-chromite hydrogenation of a mixture of linolenate and conjugated linoleate demonstrates what the program does and what is a typical output.     

Phase portrait of the dynamic system of consecutive chemical reactions: An analysis of the effect of the rate constants

The rate constant effect on the reaction path pattern, conversion, and selectivity is analyzed using the dynamic system for consecutive reversible chemical reactions. In some cases, it is impossible to simultaneously attain large values of conversion and selectivity by using a catalyst or varying the temperature.     

Phase portrait of the dynamic system of parallel chemical reactions: An analysis of the effect of the rate constants

The dynamic system describing reversible parallel chemical reactions and its phase portrait are considered. It is demonstrated how variation of the rate constants of the reactions by using a catalyst and variation of the process temperature affect the conversion and selectivity values.