化学反应平衡常数

化学反应平衡常数是化学中一个重要的物理量,在过去的教学中曾有不同的认识,许多文章对此进行了讨论.1982年我国颁布了一系列国家标准(以下简称GB标准),其中GB3102.8-82《物理化学和分子物理学的量和单位》对化学反应平衡常数作了明确的定义和规定,可以统一目前对平衡常数的不同认识,如:有哪些平衡常数?它们的表达式怎样?平衡常数有无量纲?平衡常数只是温度的函数,还是同时是温度、压力、浓度的函数?     

勒夏特列原理和化学平衡常数学习现状的调查分析和教学反思

1问题的提出化学平衡是化学反应原理的一个重要课题,新课程更不例外,但新教材引入了平衡常数,课程标准要求学生知道平衡常数的含义。那么现在学生在解决化学平衡问题时是更习惯用传统的勒夏特列原理还是新引入的平衡常数呢?平衡常数的引入能否     

基础化学教学中科学理解“化学平衡常数”的几点看法

在高中化学和大学普通化学等基础化学教学中,常常基于化学反应速率引入经验平衡常数,也有基于热力学理论引入标准平衡常数。经验平衡常数比较具体、形象,标准平衡常数比较抽象,但2者本质是一致的。经验平衡常数因存在多种形式及量纲等问题,相对复杂;标准平衡常数严格、规整,数值唯一,具有“大道至简”的特征。建议在教学中更多地从热力学角度来理解、概括化学平衡和平衡常数,在定量计算中尽可能统一使用标准平衡常数。     

表面络合模型的应用方法

本文介绍了根据表面络合机理，模拟金属和配体吸附的一般方法，讨论了某些表面络合模型的基本概念，本文的重点是本征平衡常数的测定方法，并强调了本征平衡常数与条件或热力学平衡常数的区别。     

基于氧化还原反应的配位平衡移动总反应平衡常数的推导

配位平衡的移动,可以遵从相同的“推导总反应的平衡常数”模式来做定性和定量的探讨。但在“氧化还原反应对配位平衡的影响”中,只是对化学反应做定性描述,总反应的平衡常数并没有推导,缺乏定量的探讨。原因在于氧化还原平衡常数与其他3大平衡常数不同,无法直接查得,需借助公式算出,具有隐蔽性,给总反应的推导造成了障碍。本文通过总反应平衡常数的推导解决了这个问题。     

离子强度对弱酸(碱)浓度平衡常数的影响

本文讨论了离子强度对不同弱酸（碱）浓度平衡常数的影响，指出在一定温度下，离子强度增大，将使中性分子形式的一元弱酸ＨＢ的浓度平衡常数Ｋｃａ增大；使中性分子形式的一元弱碱的浓度平衡常数Ｋｃｂ增大；使中性分子形式的二元弱酸Ｈ２Ｂ的浓度平衡常数Ｋｃａ１与Ｋｃａ２之间的比值减小。     

合成氨反应动力学平衡常数与热力学平衡常数的关系

根据当前普遍被接受的氨合成和氨分解机理,明确了氨合成及分解反应的速度控制步骤,确定了氨合成和氨分解反应的动力学方程,进而导出合成氨反应的动力学平衡常数表达式,与热力学平衡常数进行了比较,明确了2者之间的关系。有助于理解合成氨热力学平衡常数与反应速率的关系。     

《化学反应原理》中与化学平衡常数有关的几个问题

论证了中学教材为什么要引入化学平衡常数,讨论了中学教材中的化学平衡常数是经验平衡常数还是标准平衡常数,指出了应用平衡常数表达式进行计算时须遵循的规则。重现了人教版、鲁科版和苏教版《化学反应原理》教材中与化学平衡常数有关的几道例题及其解题过程,分析了解题过程中存在的问题,并提出了解决问题的策略。     

热力学标准状态与平衡常数

平衡常数是化学反应的重要热力学量,它在处理化学平衡问题时起关键作用。在目前的化学教科书中,对平衡常数的处理比较混乱,标准平衡常数Ｋ（热力学平衡常数）和经验平衡常数同时共存。其中后者是以质量作用定律为基础导出的,由于质量作用定律的局限性,这种导出是不严格的。另外在用于定量计算时在压力和浓度的单位上容易使人产生误解。为此,国际ＧＢ３１０２．８－８６不再采用经验平衡常数,只在备注栏中列出了它们的定义及性质。因此为了热力学学科的严谨性,同时有利于不同学科的交叉,在化学热力学和物理化学教学中不宜介绍经验…     

平衡常数与正逆反应速率常数之间关系的探讨

从动力学与热力学的一致性原理出发,在知道可逆化学反应机理与不知道可逆化学反应机理的两种情况下,探讨了平衡常数与正逆反应速率常数之间的关系,确定了可逆反应平衡常数在不同情况下与正逆反应速率常数之间的关系式。     

硅氮烷添加剂的水解稳定性对硅橡胶热稳定性的影响

采用一种新的方法研究了硅氮烷水解反应的动力学规律 ,根据实验数据测出硅氮烷水解速率对硅氮烷的浓度符合一级动力学关系 .计算出了几种硅氮化合物与水蒸气反应的表观活化能 ,结果表明硅氮烷的结构与其水解反应的表观活化能有密切的关系 .硅原子或氮原子上带有较大空间位阻的基团后 ,其水解稳定性提高 .其中六苯基环三硅氮烷 4的水解表观活化能为 2 14kJ mol,而苯基硅氮聚合物 5的水解表观活化能更达到 2 91 3kJ mol.添加到硅橡胶中的硅氮化合物水解表观活化能越大 ,即水解稳定性越高 ,其改进硅橡胶热稳定性的效果越好 .将 4和 5添加到硅橡胶生胶中 ,35 0℃下老化 2 4h的热失重分别为 0 96 %和 0 6 % .     

近临界水中聚丙烯腈无催化水解反应动力学

系统研究了近临界水中聚丙烯腈无催化水解反应动力学.在实验数据重现性和物料配比对PAN水解反应影响的考察基础上,系统测定了210～250℃下聚丙烯腈的水解反应动力学数据,采用元素分析仪、傅立叶变换红外光谱仪、热分析仪、凝胶色谱仪对水解产物进行了表征.结果表明,近临界水中聚丙烯腈无催化水解是可行的,其中温度与物料配比是影响水解速率的主要因素;通过控制不同水解条件,可得到不同含量的腈基(—CN)、酰胺基(—CONH2)和羧基(—COOH)二元或三元共聚物,产物侧基含量的不同有可能在不同的领域得到应用;以一级连串反应动力学模型对实验数据进行了拟合,得到了聚丙烯腈和聚丙烯酰胺水解反应活化能分别为53.37 kJ.mol-1和120.55 kJ.mol-1.     

同位素稀释质谱法测定多肽含量

利用Leu-Phe作为模型肽,建立了水解后同位素稀释质谱测定多肽含量的方法。在实验中优化了酸水解的时间,采用高效液相色谱法和质谱法证明模型肽已完全水解。水解后的氨基酸经过HPLC分离,质谱检测采用选择离子监测模式,分别检测苯丙氨酸(m/z=166)和标记苯丙氨酸(m/z=174)的离子。根据苯丙氨酸的含量计算模型肽的含量,并评定了测定结果的不确定度。     

Simultaneous determination of three flavonoid aglycones in Elsholtzia blanda by adopting orthogonal test and high-performance liquid chromatography

A new HCl hydrolysis/HPLC method, by adopting L9(34) orthogonal test to optimize hydrolysis condition, has been developed for simultaneous determination of three flavonoid aglycones in Elsholtzia blanda benth. The HCl concentration, methanol concentration, hydrolysis temperature, hydrolysis time are taking as four inspecting foctors, and the contents of luteolin, apigenin, and 5-hydroxy-6,7-dimethoxyflavone in hydrolytic solution are used as the evaluation indexes. Agilent Zorbax SB-C18 is used as analytical column. The mobile phase is a mixture of methanol-0.2% phosphoric acid (70:30, v/v), and UV detector is set at 350 nm. The flow rate is 1.0 mL/min, the temperature of column is maintained at 30 degrees C. The optimal hydrolysis conditions are 3.0M HCl, 70% methanol, 85 degrees C hydrolytic temperature and 3 h hydrolytic time. Standard curves are linear over the concentration range 8.54-85.4 microg/mL, 1.2-12 microg/mL, 9.2-92 microg/mL, and their average recoveries are 96.8%, 98.0%, and 100.5% for luteolin, apigenin, 5-hydroxy-6, 7-dimethoxyflavone, respectively. Thus, the optimum hydrolysis condition is relatively gentle, and the HPLC method is proved to be simple, accurate, and sensitive, so it will be able be applied to quality control of medicinal plant of Elsholtzia blanda.     

Systems based on the hydrophobically modified poly(ethylene imines) and surfactants: Aggregation and catalysis

The aggregation in aqueous systems of hydrophobically modified poly(ethylene imines) and their mixtures with cationic surfactants, as well as the catalytic activity of these compositions in the hydrolysis of O-4-nitrophenyl-O-ethylchloromethylphosphonate, are studied by conductometry, tensiometry, light-scattering, and viscometry methods. Critical association concentration, hydrodynamic radii of polymer and polymer-colloid aggregates formed in such systems, as well as kinetic parameters of hydrolysis are determined.     

Aqueous solutions that model the cytosol: studies on polarity, chemical reactivity and enzyme kinetics

Concentrated solutions of a series of organic compounds have been prepared and the effects of these solutes on the properties of the solvent system assessed as a function of their concentration and nature. Polarity, as measured by Reichardt's E(T)(30) probe, exhibits a linear variation with both solute and water concentration for simple solutes. Non-linear behaviour was also observed and is associated with preferential solvation or binding of the E(T)(30) probe molecule by the added solute. The observed trends in polarity are mirrored in the effects of these solutes on chemical reactivity and enzyme kinetics. Environmental effects on the kinetics of hydrolysis of 4-nitrophenyl dichloroacetate, the hydronium-ion catalysed hydrolysis of 2-(4-nitrophenoxy)-tetrahydropyran, the acyl transfer reaction between 4-nitrophenyl acetate and TRIS, the Diels-Alder reaction between 1,4-naphthoquinone and cyclopentadiene and the trypsin-catalysed hydrolysis of 4-nitrophenyl acetate are reported and discussed in terms of the properties of the solutes and the mechanistic requirements of these reactions. Linear correlations were observed between the logarithms of the rate constants for the acetal hydrolysis, acyl transfer and Diels-Alder reactions with water concentration. Since the latter varies linearly with E(T)(30), this indicates a linear free energy relationship between solution polarity and chemical reactivity.     

含杂环聚芳醚腈酮的亲水改性

为得到适合于耐高温水性涂料用的亲水性树脂,在碱性条件下对含有二氮杂萘酮结构的耐高温聚合物聚芳醚腈酮(PPENK)进行了亲水改性,选定不同反应时间的改性树脂HPPENKa(0.5 h)、HPPENKb(1.5 h)和HPPENKc(3.5 h),测定其玻璃化转变温度(Tg)、热失重温度、水接触角和溶解性,研究改性聚合物的性能变化.结果表明,随着反应时间的延长,氰基转化率提高,水解产物Tg增加,热失重温度有所降低,水解前后的溶解性能有很大变化,亲水性能明显增强,例如,当氰基转化率为93.82%时,HPPENK膜的水接触角达到54.4°,比PPENK膜的水接触角(75.3°)减小了20.9°.同时,甄选不同的反应共溶剂、反应温度以及碱浓度,考察其对反应的影响,结果表明,当反应温度为120℃6、mol/L NaOH溶液、以DMAc作为反应的共溶剂时对反应较为有利.制备了基于3种改性树脂的水分散体,其静置稳定性依次为HPPENKc>HPPENKb>HPPENKa,其中HPPENKc水分散体较稳定,30天内未出现沉淀.改性聚合物的结构经FT IR和1H-NMR表征.     

Cellulose and hemicellulose hydrolysis models for application to current and novel pretreatment processes

Acids catalyze the hydrolysis of cellulose and hemicellulose to produce sugars that organisms can ferment to ethanol and other products. However, advanced low- and no-acid technologies are critical if we are to reduce bioethanol costs to be competitive as a pure fuel. We believe carbohy drate oligomers play a key role in explaining the performance of such hydrolysis processes and that kinetic models would help us understand their role. Various investigations have developed reaction rate expressions based on an Arrhenius temperature dependence that is first order in substrate concentration and close to first order in acid concentration. In this article, we evaluate these existing hydrolysis models with the goal of providing a foundation for a unified model that can predict performance of both current and novel pretreatment process configurations.     

水解制备球形TiO2及其水解过程动力学

以硫酸钛(Ti(SO4)2)为前驱物水解得到超细球形TiO2. 研究了水解过程中前驱物浓度和体系温度对水解速率的影响, 并对实验值进行了拟合, 得到水解TiO2的质量分数与水解时间呈良好的指数关系, 根据Avrami方程进一步验证了拟合的可靠性. 分析了水解介质的影响作用, 确定介电常数和zeta电位也是影响水解速率的重要因素, 因此可通过改变溶剂成分来调节介电常数和zeta电位, 从而达到控制Ti(SO4)2水解速率的目的. 实验结果表明, Ti(SO4)2水解制备TiO2的过程中, 较低的前驱物浓度, 较高的水解温度和合适的溶剂体系有利于得到粒径分布窄、分散性好的TiO2.     

MICELLAR CATALYSIS OF COMPOSITE REACTIONS I MICELLAR EFFECT ON THE CONSECUTIVE FIRST ORDER REACTION

The micellar catalytic model (or the consecutive first order reaction has been proposed in this paper. It was applied to the alkaline hydrolysis of dimethyl phthalate in micellar solutions of surfactants (CTAB, SDS and Triton X-100), and the alkaline hydrolysis of bis (2,4-dinitrophenyl) posphate in CTAB micellar solution. Rate constants obtained in micellar phase indicate that the two steps of alkaline hydrolysis of dimethyl phthalate are both inhibited by all of the surfactants investigated. CTAB micelle exhibits a greater catalytic effect on the alkaline hydrolysis of bis (2, 4-dinitrophenyl) phosphate. this may be arised from the local concentration effect of hydroxide ion in CTAB micellar phase. Nevertheless. the second order rate constant of bis-(2, 4-dinitrophenyl) phosphate in the micellar phase is smaller than that in the bulk phase.