建立反应速率方程的新方法

对于有一定级数的反应,不论反应级数是几,建立反应速率方程时都可以用非线性拟合法来完成。该方法分为两步。第一步,初次对实验数据进行非线性拟合,从而得到反应级数;第二步,借助已得到的反应级数再次对实验数据进行非线性拟合,从而得到反应速率常数。与传统建立反应速率方程的方法相比较,非线性拟合法不仅简单易操作,而且处理结果准确、图线美观大方。     

关于反应级数的确定方法

研究化学反应动力学 ,一般首先从实验数据确定其反应级数 ,这不仅是因为反应级数体现浓度对反应速率的影响程度 ,而且是推测反应机理的最重要依据。大多物理化学教材中 ,详细讨论了形式为 - ｄｃｄｔ=ｋｃｎ 类型速率方程的反应级数的确定方法 ,主要有 3种 :积分法 ,微分法和半衰期法。本文将从实用性和准确性的角度予以讨论 ,并提出一个合适的和方便的方法。　　 (1 )关于微分法。将速率方程取对数 :ｌｎ - ｄｃｄｔ =ｎｌｎｃ +ｌｎｋ ,则ｌｎ - ｄｃｄｔ ～ｌｎｃ为线性关系 ,其斜率为ｎ。求ｎ的具体步骤为 :作ｃ～ｔ曲线 ;在曲线上取若…     

一种确定反应级数的简便方法

一种确定反应级数的简便方法陈平初（武汉华中师范大学化学系４３００７０）对于速率方程为的化学反应，为确定反应级数ｎ，可按等时间间隔读取一组浓度数据假定反应进程中某一时刻（ｔ１）为反应起点，则该时刻的反应物浓度（ｃ１）为起始浓度，以表示反应物浓度由ｃ１变...     

用非线性的最小二乘法确定化学反应动力学参数的程序

在化学反应动力学的实验数据处理中常常遇到在已知反应速率的微分方程组(简称速率方程,REQ),或其解所示各组元浓度对时间依赖的函数关系(简称动力学方程,KEQ)的形式时,如何由实验数据确定这些方程中的化学反应动力学参数(主要是一些反应速率常数)。关于这一问题的数学原理,过去文献上已有报     

n级反应的热动力学对比进度法

在化学反应的热动力学研究中,根据一次实验的热谱曲线来确定一个未知反应的级数,是一项很有理论和实际意义的工作.本文建立了n级反应的热动力学对比进度法.应用此法可判定反应级数和计算速率常数,并用实验及文献数据验证了本文方法的正确性.     

Excel在基础无机化学实验数据处理中的应用

介绍了一种处理基础无机化学实验数据的方法,即用Microsoft Office系列中的Excel软件自动完成数据的分析和图表的处理.以"化学反应速率"及"碘化铅溶度积常数的测定"的实验内容为例,通过实验测得的反应速率和c(I-) 标准曲线吸光度及PbI2饱和溶液的制备.用Excel进行数据分析、公式计算和图表处理,找出了线形拟合关系,确定了反应级数,计算出了速率方程、速率常数、活化能和溶度积常数,以完整详实地实验记录将处理的结果完整地展示出来.方法具有方便快捷、精确度高、操作简便等优点.减少人工处理数据带来的误差.是本科生学习处理专业实验数据的基本方法之一.     

特征参量法1: 简单级数反应的热动力学研究法

建立了测定热动力学体系冷却常数的线性拟合法和简单级数反应通用的热动力学研究法---特征参量法。导出了简单级数反应的动力学参数Kn和速率常数kn的通用计算式。应用冷却常数的线性拟合法在不同温度下测定了两个反应体系的冷却常数, 探讨了温度、浓度、介质及装样方式对冷却常数的影响。应用简单级数反应的特征参量法研究了一级、二级、三级和分数级反应的热动力学, 结果文献值吻合。讨论了热动力学体系的冷却常数对速率常数计算结果的影响。     

特征参量法1: 简单级数反应的热动力学研究法

建立了测定热动力学体系冷却常数的线性拟合法和简单级数反应通用的热动力学研究法---特征参量法。导出了简单级数反应的动力学参数Kn和速率常数kn的通用计算式。应用冷却常数的线性拟合法在不同温度下测定了两个反应体系的冷却常数, 探讨了温度、浓度、介质及装样方式对冷却常数的影响。应用简单级数反应的特征参量法研究了一级、二级、三级和分数级反应的热动力学, 结果文献值吻合。讨论了热动力学体系的冷却常数对速率常数计算结果的影响。     

简单级数反应的特征时间法

在化学反应的热动力学研究中,建立适宜的研究方法从热谱曲线上获得动力学参数是其中心内容．目前,已先后建立了无量纳参数法［‘j,对比进度法［‘］,模拟热谱曲线法［’］等并已得到广泛应用［‘j．这些方法均未直接利用到时间参量,热谱解析过程都较为复杂．我们在前文［到将时间作为已知参数,建立一种不需要反应进行到底就可获得化学反应速率常数的简单级数反应的时间变量法．但是,该法数据处理时需要取三个时间点以及相应的热谱数据,而时间滞后效应对于取多个时间点所带来的动力学计算误差有时是不能忽略的．因此,本文基于热动力…     

时间参量法Ⅱ.简单级数反应的热谱面积差法

从简单级数反应的热动力学方程出发,将时间作为已知参量,提出了一种新的热动力学研究法——简单级数反应的热谱面积差法.该法不需反应进行到底便可求解化学反应的速率常数.实验结果验证了方法的正确性.     

I. Numerical nonlinear analysis: differential methods and optimization applied to chemical reaction rate determination

The primary emphasis of this work on kinetics is to illustrate the a posteriori approach to applied nonlinear analysis, where focus on data may also lead to novel outcomes, as may also be the case with the current a priori tendencies of applied analysis, which relies on axioms or constructs concerning the nature of the observable. Here, methods for the determination of chemical rate constants are developed and discussed utilizing nonlinear analysis which does not require exact knowledge of initial reactant concentrations. These methods are compared with those derived from standard methodology for known chemical reactions studied by eminent kineticists and in one case with a reaction whose initial reactant concentration was in doubt. These gradient methods are shown to be consistent with the standard methods on average, and could readily serve as alternatives for standard conditions and can be used for studies where there are limits or unknowns in the initial conditions, such as in the burgeoning fields of astrophysics and astrochemistry, forensics, archeology and biology where the standard methods are not applicable. All four reactions studied exhibited semi-sinusoidal-like change with reactant concentration change which standard integral methods have not highlighted, and which seems to constitute the observation of a new effect. Reasons based on two mechanisms are given for this observation, and experiments are suggested that can discriminate between these two factors. Although first and second order reactions were investigated here, the method applies to arbitrary fractional orders by polynomial expansion of the rate decay curves where closed form integrated expressions do not exist at present. Integral methods for the above will be investigated next.     

Application of different polarimetric methods for the analysis of enzyme-catalyzed enantioselective reactions

Identification of model parameters in kinetic equations requires the determination of reactant concentrations in the course of time. In the case of enzyme catalyzed enantioselective reactions, three different polarimetric methods were used for concentration measurements obtained in both initial rate experiments and under dynamically changing conditions. Two on-line methods for the determination of different numbers of chiral species and a more universal off-line method were applied. For the investigated substrate 5-benzylhydantoin and the enzyme hydantoinase it is shown, that the obtained polarimetric data are most suitable for identification of kinetic parameters. Furthermore, it is demonstrated that on-line data of only one conversion allow for an assessment of an enzyme with regard to its enantioselectivity.     

Reversed-phase ion-pair liquid chromatographic method for determination of reaction equilibria involving ionic species: exemplification of the method using ligand substitution reactions of ethylenediaminetetraacetatochromium(III) ion with acetate and phosphate ions

A reversed-phase ion-pair liquid chromatographic method is presented for the determination of reaction equilibria involving ionic species of the same charge sign as reactant and product compounds. It has been demonstrated that ion-exchange chromatography or reversed-phase ion-pair chromatography is a useful tool for the determination of equilibrium constants of chemical reactions involving ionic species such as metal complexation reactions. Previous work with these methods has been based on the assumption that the limiting retention factors of the reactant and product species are constant independent of concentration of the chemical species (X) in the mobile phase, which reacts with the analyte compound. However, when all the reactant and product species are ions of the same charge sign as that of the species X, it is virtually impossible to apply these methods to the equilibrium constant determination because the retention factors of both the reactant and product species may depend on the concentration of X. In this study, an alternative approach was developed that estimates the limiting retention factors of ionic species from the dependence of the retention factor on the ionic strength of the mobile phase. Ligand substitution reactions of ethylenediaminetetraacetatochromium(III) ion with acetate and phosphate ions were used as model reactions to test this method. The equilibrium constants determined by this method are in good agreement with those obtained by a UV-visible spectrophotometric method.     

Application of different polarimetric methods for the analysis of enzyme-catalyzed enantioselective reactions

Identification of model parameters in kinetic equations requires the determination of reactant concentrations in the course of time. In the case of enzyme catalyzed enantioselective reactions, three different polarimetric methods were used for concentration measurements obtained in both initial rate experiments and under dynamically changing conditions. Two on-line methods for the determination of different numbers of chiral species and a more universal off-line method were applied. For the investigated substrate 5-benzylhydantoin and the enzyme hydantoinase it is shown, that the obtained polarimetric data are most suitable for identification of kinetic parameters. Furthermore, it is demonstrated that on-line data of only one conversion allow for an assessment of an enzyme with regard to its enantioselectivity. Received: 20 October 1998 / Revised: 28 December 1998 / Accepted: 4 January 1999     

甲基丙烯酸甲酯聚合动力学和分子量模型及仿真

考虑甲基丙烯酸甲酯聚合过程中体积收缩，反应物和生成物的浓度变化，以及由于凝胶、玻璃化和笼闭等效应对各速率常数和物性参数的影响，从基元反应和物料平衡出发，推导了半间歇，有链转移剂参与情况下的聚合动力学和分子量模型。用模型仿真计算了聚合温度、引发剂、溶剂和链转移剂的种类和浓度等对甲基丙烯酸甲酯聚合动力学和聚合过程中分子量变化的影响规律，并与实验和文献数据进行比较。     

D2EHDTPA-TOA反协同萃取镉的速率方程

以恒界面池法研究了D2EHDTPA（二（2-乙基己基）二硫代磷酸）-TOA（三辛胺）反协同萃取镉的界面反应速率方程.萃取历程由若干个相转移（在本体相与界面相之间的物质转移）过程和若干个反应组成.萃取的速率方程为 r=1.42*10^-7[Cd²⁺]^0.42[BHA]^0.47/[B]^0.85[H⁺]^0.21 （mol•m^-2•s^-1） 探讨了萃取速率方程中非整数反应物级数的物理意义.Freundlich因子n越大,物质在界面层所受排斥力越大.萃取过程的表观活化能E=44.2 kJ•mol－1,萃取反应的焓变ΔH=72.9 kJ•mol－1.讨论了由不同的界面模型而导致不能通融的萃取动力学机理的问题.     

What can we learn about the mechanisms of thermal decompositions of solids from kinetic measurements?

Aspects of the theories that are conventionally and widely used for the kinetic analyses of thermal decompositions of solids, crystolysis reactions, are discussed critically. Particular emphasis is placed on shortcomings which arise because reaction models, originally developed for simple homogeneous reactions, have been extended, without adequate justification, to represent heterogeneous breakdowns of crystalline reactants. A further difficulty in the mechanistic interpretation of kinetic data obtained for solid-state reactions is that these rate measurements are often influenced by secondary controls. These include: (i) variations of reactant properties (particle sizes, reactant imperfections, nucleation and growth steps, etc.), (ii) the effects of reaction reversibility, of self-cooling, etc. and (iii) complex reaction mechanisms (concurrent and/or consecutive reactions, melting, etc.). A consequence of the contributions from these secondary rate controls is that the magnitudes of many reported kinetic parameters are empirical and results of chemical significance are not necessarily obtained by the most frequently used methods of rate data interpretation. Insights into the chemistry, controls and mechanisms of solid-state decompositions, in general, require more detailed and more extensive kinetic observations than are usually made. The value of complementary investigations, including microscopy, diffraction, etc., in interpreting measured rate data is also emphasized. Three different approaches to the formulation of theory generally applicable to crystolysis reactions are distinguished in the literature. These are: (i) acceptance that the concepts of homogeneous reaction kinetics are (approximately) applicable (assumed by many researchers), (ii) detailed examination of all experimentally accessible aspects of reaction chemistry, but with reduced emphasis on reaction kinetics (Boldyrev) and (iii) identification of rate control with a reactant vaporization step (L’vov). From the literature it appears that, while the foundations of the widely used model (i) remain unsatisfactory, the alternatives, (ii) and (iii), have not yet found favour. Currently, there appears to be no interest in, or discernible effort being directed towards, resolving this unsustainable situation in which three alternative theories remain available to account for the same phenomena. Surely, this is an unacceptable and unsustainable situation in a scientific discipline and requires urgent resolution?     

A comparison of isoconversional and model-fitting approaches to kinetic parameter estimation and application predictions

A variety of isoconversional and model fitting approaches, all of which use multiple heating schedules, are used to analyze selected data from the ICTAC kinetics and lifetime projects as well as additional simulated data sets created for this work. The objective is to compare the accuracy and suitability of various approaches for various types of chemical reactions. The various simulated data sets show that model fitting and isoconversional methods have comparable reliability for extrapolation outside the range of calibration. First, there is as much variability in prediction for various isoconversional methods as there is between isoconversional methods as a group and different plausible explicit models. Of the three isoconversional models investigated, the Friedman method is usually the most accurate. This is particularly true for energetic materials that have a drop in apparent activation energy in the latter stages of reaction, which leads to a delayed onset of rapid autocatalysis at lower temperatures. It is difficult to determine a priori whether isoconversional or model fitting approaches will give more accurate predictions. The greatest reliability is attained by using both the isoconversional and model fitting approaches on a combination of isothermal and constant heating rate data.     

Stopped-flow electrospray ionization mass spectrometry: a new method for studying chemical reaction kinetics in solution

In this work a new mass spectrometry based method for monitoring the kinetics of chemical reactions in solution is described. A stopped-flow mixing instrument is coupled to an electrospray ionization (ESI) mass spectrometer via a novel type of interface. Chemical reactions are initiated by rapid mixing of two reactant solutions. The mixture is instantaneously transferred to a reaction tube where the kinetics can be monitored in real-time by ESI mass spectrometry. With the current setup, a time window from 2.5 to 36 seconds after mixing of the reactants can be monitored. The experimental setup is used to study the kinetics of acetylcholine hydrolysis under alkaline conditions as a function of pH. The intensities of reactant (acetylcholine) and product (choline) ions are monitored simultaneously as a function of time. The reaction is carried out under pseudo-first-order conditions and the intensity-time curves are well described by single exponentials. The rate constants determined from these fits compare favorably with previous data from the literature.