直接曲线拟合法确定反应速率方程

从实验数据确定反应速率方程是化学动力学的重要内容之一。物理化学教材与文献中多依据反应物浓度或者分压进行直线拟合,这些方法的数据处理工作量大。很多化学反应是通过测量系统的物理性质来研究化学反应动力学过程,在教材和文献中缺少从物理性质直接拟合得到速率方程的普遍适用的方法。本文提出了一种由浓度-时间数据或物理性质-时间数据直接曲线拟合得到简单级数反应速率方程的新方法,通过曲线拟合同时求出反应级数与速率常数,利用实例对简单级数反应进行了验证。本文提出的方法是化学动力学"速率方程的确定"内容的创新,对确定简单级数反应速率方程具有重要意义。     

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…     

以环己烷为溶剂菲的催化加氢裂解动力学研究

在微型反应器中,以氧化铝-分子筛为担体的Ni-Mo催化剂对环己烷中的菲的加氢裂解动力学进行了研究。考察了温度、压力和气液比对反应的影响。利用非线性Marquart方法对实验数据进行了回归,得到幂指数随温度倒数线性变化的幂速率方程,经动力学模型识别与检验,建立了菲加氢裂解反应的动力学速率方程。     

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.     

Tl^3^+─H2O2─Fe^2^+体系的反应动力学研究

本文用Tl(I)离子选择性电极测定了Tl^3^+-H2O2-Fe^2^+体系的反应参数, 据此计算了该体系的反应级数, 得到了反应速率方程式, 对该反应体系的反应机理进行了探讨, 并用稳态处理法对所提出机理进行验证, 其结论与实验所得速率方程完全符合。     

Tl^3^+─H2O2─Fe^2^+体系的反应动力学研究

本文用Tl(I)离子选择性电极测定了Tl^3^+-H2O2-Fe^2^+体系的反应参数, 据此计算了该体系的反应级数, 得到了反应速率方程式, 对该反应体系的反应机理进行了探讨, 并用稳态处理法对所提出机理进行验证, 其结论与实验所得速率方程完全符合。     

由DTG曲线确定反应级数的新方法

利用动态热重曲线求固相反应动力学参数的方法很多,如微分差分法,微分法和积分法等,有关数据处理方法中,反应级数n的获得尤为重要,因为有的需要预先知道反应级数或通过尝试才能求得反应级数;如Coats-redfern法,最大速率法等。有的方法虽可由实验直接确定反应级数,但精度低。前文曾采用逐步逼进法对Coats-redfern法中最佳n值的获得进行了讨论。本文根据DTG-TG曲线的特点,探求一种简便获得反应级数n的方法,通过研究CaC_2O_4·H_2O的分解反应,对该方法的可靠性进行论证。     

MATLAB在动力学实验数据处理中的应用

将MATLAB 数学软件编写程序用于物理化学实验“丙酮碘化反应速率方程”的数据处理与绘图,根据孤立法设计实验步骤以此推得反应级数,所得结果准确度高,避免了传统数据处理方法所带来的人为误差,具有方便、快速与直观等优点,可以补充和改进物理化学实验的教学。     

脂肪酶催化乳酸与乙醇合成乳酸乙酯的反应动力学

对脂肪酶催化乳酸与乙醇合成乳酸乙酯反应的动力学进行了研究,根据乒乓机制和双底物抑制的特性建立了反应速率方程.反应时间常数(tR)和扩散时间常数(tD)的计算结果表明,酯化反应速率未受到明显的限制.反应速率方程可以很好地预测实验结果,由非线性拟合得到的动力学参数中,乳酸(A)和乙醇(B)的抑制常数分别为KiA=10.7mmol/L和KiB=275.0mmol/L.这说明乳酸作为短链极性脂肪酸,对酶的失活作用远大于乙醇.乳酸在微液层中聚集并产生了使酶失活的低pH值环境,同时在酯化反应中存在竞争性抑制作用.     

铜(II)与四(间甲基)苯基卟啉镉(II)取代反应动力学

用分光光度法研究了二甲亚砜溶液中, 氯化铜与meso-四(间甲基)苯基卟啉镉(Ⅱ)(Cd(Ⅱ)P)亲电取代反应的动力学. 讨论了影响反应的因素, CuCl_2+Cd(Ⅱ)P→Cu(Ⅱ)P+CdCl_2提出了反应机理并进行了验证. 用AST286微机对实验数据进行非线性最小二乘法拟合, 得到拟合曲线及似平衡步的平衡常数K及其它基元步骤的速率常数k_1, k_(-1), k_2. 研究了温度对反应的影响, 求得似平衡步的△_rH_m~-θ-, △_rS_m~-θ-及其它基元步骤的活化参数△~≠H_m, △~≠S_m.     

速率常数-秩分析法在化学反应过程分析中的应用

针对化学反应动力学谱-吸收光谱组成的两维数据,提出了以优化速率常数而消去反应物波谱信息为减秩手段的速率常数-秩分析法(RCRA).结果表明,RCRA在一次优化过程中可同时获得两个最优解,分别对应于两步速率常数.在获得动力学参数的前提下,利用最小二乘回归可解出包括中间体在内的各组分的吸收光谱.该方法用于处理苯胺电解降解的两维数据,发现苯胺降解过程中有一种表观中间体存在,降解过程符合一级连串反应模型.     

Experimental and Theoretical Insight into the Kinetics and Mechanism of the Synthesis Reaction of 2,3‐Dihydro‐2‐phenylquinazolin‐4(1H)‐one Catalyzed in Formic Acid

An efficient and simple method has been developed for the synthesis of 2,3‐dihydro‐2‐phenylquinazolin‐4(1H )‐one catalyzed in formic acid. Also, the synthesis reaction between benzaldehyde and 2‐aminobenzamid was monitored spectrally. On the basis of the kinetic data obtained by the UV–vis spectrophotometry, both the first and second steps of the speculative five steps mechanism were enabled to be a rate‐determining step and also reaction showed second‐order kinetics. Considering information obtained by the stopped‐flow technique indicated that the first step is certainly a fast step. Moreover, the reaction was energetically and thermodynamically evaluated using theoretical methods and results were profoundly compared with the experimental approaches. Herein, theoretical rate constants were obtained using potential energy surfaces and the transition state theory at the B3LYP/6–311+G** level of theory. The Winger method was also applied to describe the tunneling effects. Calculations showed that the second step was the rate‐determining step in accordance with the experimental data. It is also found that the oxidation step was the fastest step in the proposed mechanism. For all five steps, two possibilities were considered for generating the probable product by using the thermodynamic parameters and kinetic data. Thermodynamic parameters also showed an exothermic reaction.     

Equivalency of Kinetic Schemes: Causes and an Analysis of Some Model Fitting Algorithms

The same experimental data can often be equally well described by multiple mathematically equivalent kinetic schemes. In the present work, we investigate several model‐fitting algorithms and their ability to distinguish between mechanisms and derive the correct kinetic parameters for several different reaction classes involving consecutive reactions. We have conducted numerical experiments using synthetic experimental data for six classes of consecutive reactions involving different combinations of first‐ and second‐order processes. The synthetic data mimic time‐dependent absorption data as would be obtained from spectroscopic investigations of chemical kinetic processes. The connections between mathematically equivalent solutions are investigated, and analytical expressions describing these connections are derived. Ten optimization algorithms based on nonlinear least squares methods are compared in terms of their computational cost and frequency of convergence to global solutions. Performance is discussed, and a preferred method is recommended. A response surface visualization technique of projecting five‐dimensional data onto the three‐dimensional search space of the minimal function values is developed.     

Mechanism of the Oxidation of 3,3′,5,5′-Tetramethylbenzidine Catalyzed by Peroxidase-Like Pt Nanoparticles Immobilized in Spherical Polyelectrolyte Brushes: A Kinetic Study

Experimental and kinetic modelling studies are presented to investigate the mechanism of 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation by hydrogen peroxide (H₂O₂) catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes (SPB−Pt). Due to the high stability of SPB−Pt colloidal, this reaction can be monitored precisely in situ by UV/VIS spectroscopy. The time-dependent concentration of the blue-colored oxidation product of TMB expressed by different kinetic models was used to simulate the experimental data by a genetic fitting algorithm. After falsifying the models with abundant experimental data, it is found that both H₂O₂ and TMB adsorb on the surface of Pt nanoparticles to react, indicating that the reaction follows the Langmuir–Hinshelwood mechanism. A true rate constant k, characterizing the rate-determining step of the reaction and which is independent on the amount of catalysts used, is obtained for the first time. Furthermore, it is found that the product adsorbes strongly on the surface of nanoparticles, thus inhibiting the reaction. The entire analysis provides a new perspective to study the catalytic mechanism and evaluate the catalytic activity of the peroxidase-like nanoparticles.     

Extraction of the contribution of kinetic profile for reaction of a chemical species in unknown matrices by standard addition method

A new and simple strategy is applied to resolve kinetic profile for the reaction of an analyte in unknown matrices, using standard addition method (SAM). The proposed method uses kinetic spectrophotometric data obtained by standard addition of analyte into unknown mixtures followed by the reaction of analyte with a proper reagent. The proposed method extracts kinetic profile for the reaction of an analyte by averaging the kinetic profiles obtained by subtraction of kinetic profiles after and before standard addition. The rate constant can be obtained using computational curve fitting. The performance of method was evaluated by using synthetic data as well as several experimental data sets. The proposed method can be applied to obtain kinetic profiles of the reactions in the presence of additive interference as well as multiplicative interferences. Hydroxylation reaction of diphenylcarbazide (DPCI) in the presence of diphenylcarbazone (DPCO) as a real system at various pHs was also studied by the present method. The rate constant and the order of the hydroxylation reaction were determined from extracted kinetic profiles.     

A multidimensional approach to the analysis of chemical shift titration experiments in the frame of a multiple reaction scheme

We present a method for fitting curves acquired by chemical shift titration experiments, in the frame of a three‐step complexation mechanism. To that end, we have implemented a fitting procedure, based on a nonlinear least squares fitting method, that determines the best fitting curve using a “coarse grid search” approach and provides distributions for the different parameters of the complexation model that are compatible with the experimental precision. The resulting analysis protocol is first described and validated on a theoretical data set. We show its ability to converge to the true parameter values of the simulated reaction scheme and to evaluate complexation constants together with multidimensional uncertainties. Then, we apply this protocol to the study of the supramolecular interactions, in aqueous solution, between a lanthanide complex and three different model molecules, using NMR titration experiments. We show that within the uncertainty that can be evaluated from the parameter distributions generated during our analysis, the affinities between the lanthanide derivative and each model molecule can be discriminated, and we propose values for the corresponding thermodynamic constants. Copyright © 2013 John Wiley & Sons, Ltd.     

利用减秩因子分析法同时优化确定化学反应级数和速率常数

通过对反应过程中在线测得的动力学谱-光谱二维数据矩阵进行主成分分析，可确定化学反应过程存在的组分数。提出用优化动力学参数-减秩因子分析法解析二维数据矩阵，对未知动力学模型的复杂反应可同时优化求解第一步反应的级数和速率常数。模拟二维数据验证了该方法的可行性。该方法用于高锰酸钾氧化溴化钠的反应过程中测得的二维数据的解析，结果表明：高锰酸钾的还原过程符合0级反应模型。     

液相法苯选择加氢制环己烯催化反应动力学方程

 测定了Ru－M－B／ZrO2催化剂上选择加氢制环己烯反应过程中苯、环己烯及环己烷浓度随时间变化的c～t曲线，获得了苯选择加氢制环己烯反应中各步反应的级数和速率常数等动力学参数．结果给出，苯转化的反应级数对苯为1，对氢低压下为2，高压下为0；环己烯继续加氢生成环己烷的反应级数对环己烯为0，对氢低压下为2，高压下为0．在此基础上建立了苯选择加氢制环己烯各步反应的动力学方程，并对动力学方程进行了验证．