由弱酸的酸常数求相关半反应标准电极电势的方法

从弱酸的酸常数出发,分别利用体系的电极电势、原电池原理和金属配离子模式三种方法对相关半反应的标准电极电势进行了求解。对三种方法的思路和本质进行了阐述,加深了弱酸的酸常数与相关半反应标准电极电势关系的理解。     

探究用热力学方法计算电极电势的公式

针对教材上利用热力学方法计算电极电势的两个公式φθ=[∑νBΔfGmθ（B）]/（nF）和E3θ=n1E1θn＋3 n2E2θ的谬误,通过举例对两个公式进行了详细的推导。说明了φθ=[∑νBΔfGmθ（B）]/（nF）和只能用于失电子半反应计算标准电极电势,补充了对于得电子的半反应计算标准电极电势的公式φθ=ΔrGmθ...     

粒径对纳米氧化锌颗粒电极电势和热力学性质的影响

为探究纳米颗粒粒径对电极电化学热力学的影响规律,从理论上分析了纳米电极电化学热力学函数对粒径的依赖关系。以纳米氧化锌为例,通过测定不同温度下、不同粒径纳米氧化锌的电极电势,得到标准电极电势、温度系数和电极反应热力学函数随粒径的变化规律。理论和实验结果都表明,当纳米氧化锌粒径减小时,标准电极电势和相应电极反应的平衡常数增大,而温度系数、摩尔吉布斯能变、焓变和熵变减小。同时,在实验范围内,这些量都与粒径的倒数存在线性关系。     

图示法推导标准电极电势与平衡常数关系初探

大一新生在进行弱电解质、难溶电解质及配离子所形成的电对的标准电极电势计算时存在畏难心理,且学习效果不理想。针对这些问题,本文探索了使用图示的方法推导这三种电对的标准电极电势与其平衡常数的关系。这一推导方法简单、直观、学生一目了然,容易掌握,并且突出了浓度对电极电势的影响,即能斯特方程的应用氧化还原平衡这一教学重点。实践证明,使用这种方法教学,学生能更好的掌握这些电对标准电极电势的计算,教学效果也有明显提高。     

醋酸-醋酐溶液中石墨电极上Mn(Ⅲ)/Mn(Ⅱ)电对研究

平衡电极电势实验确定了25℃时石墨电极在1.5 mol/L醋酸钾 (醋酸-醋酐)(3:1体积比)溶液中Mn(Ⅲ)/Mn(Ⅱ)的条件电极电势为0.720 V(vs SCE);采用电势扫描和旋转圆盘电极技术研究了醋酸-醋酐溶液中石墨电极上Mn(Ⅲ)/Mn(Ⅱ)电对的阳极氧化动力学,结果表明:Mn(Ⅱ)阳极氧化成Mn(Ⅲ)的电极反应控制步骤属扩散-电荷传递混合控制过程,阳极传递系数β=0.183,交换电流密度i0=5.80×10-5 A/cm2,阳极标准反应速度常数ka=9.16×10-8 m/s,Mn(Ⅱ)和OAc-的反应级数均为一级.     

以电极电势书写能斯特方程

能斯特方程是联系电化学与热力学的桥梁,表达了在某温度下电池的电动势与标准电动势及参与反应体系中各物质的浓度或活度之间的关系,在电化学基础中占据重要的地位。鉴于在学习能斯特方程过程中,对于复杂的化学反应直接根据电池的总反应书写能斯特方程时,对数项中各物质的浓度书写容易出错,通过探索发现先写出每一电极电势的能斯特方程,然后用正极的电极电势减去负极电极电势就可得到电池电动势的能斯特方程,可以避免这些问题,使能斯特方程的书写变得准确无误、方便简单。     

电解池中电极产物的判断

电极产物的判断主要依据电极电势的大小。解析标准电极电势、析出电极电势、超电势、极化现象等相关的概念,分析判断电极产物的规则,结合实例分析判断电极产物的具体方法和依据,并归纳电极产物的一般规律。     

二氧化氯消毒处理含溴离子水防止溴酸盐产生的研究

该文从消毒过程中涉及到的氧化还原反应的电极电势出发,借助元素电势图以及半反应的pH-电势图,发现当处理水pH为7时,二氧化氯还原为亚氯酸根的电极电势为0.95 V,低于溴离子被氧化成溴酸盐的电极电势(1.03 V),从而在理论上解释了用二氧化氯消毒处理饮用水时,即使在处理水中含有溴离子的情况下,也不会形成溴酸盐,该结论也得到了实验数据的支持。     

三大平衡对电极电势的影响

从电极电势的Nernst方程出发，利用化学平衡的有关知识，通过分析三大平衡(沉淀平衡、配位平衡和酸碱平衡)的平衡常数K值(K_sp、K_s、K_a)对电极电势的影响，以期认识三大平衡与氧化还原平衡的内在联系，加深对知识点之间的普通联系和理解，便于学生形成知识网络。在讨论三大平衡参与涉及的氧化-还原有关问题时，不论是定性还是定量，只需明确电极电势的实质内涵，然后求得其代数值大小，许多看似较难的问题均能迎刃而解。     

氧化还原平衡在无机杂质分离中的应用

在无机试剂的生产中,常见的杂质如Fe、Cu、Co、Ni、Cr、Mn、Sn、Pb……等,它们都有多种氧化态。分离这些杂质时,广泛地应用其氧化态和还原态之间的变化规律,并且还经常考虑和酸碱平衡、沉淀平衡和络合平衡的联系。已知的用标准氢电极作标准电极所测得的许多氧化还原电对的标准电极电势E~0值,可以用来表示氧化型得电子或还原型失电子的能     

Thermodynamics of reactions during the electrosynthesis of peroxodisulphates

On the basis of recent more exact values of chemical thermodynamic properties of individual substances the standard electrode potentials and equilibrium constants of various electrode and chemical reactions carried out during the electrosynthesis of peroxodisulphates were recalculated. In some cases, quite remarkable differences in comparison to the values according to Latimer's data have been obtained. For the first time the standard potential of the anodic discharge of Caro's acid as well as the equilibrium constant of the hydrolysis of peroxodisulphate to peroxomonosulphate ions have been evaluated.     

Free energy coupling of electron transfer and ion transfer in two-immiscible fluid systems

Free energy coupling of electron and ion transfers across a liquid-liquid interface is treated theoretically assuming electroneutrality of each phase and complete dissociation of electrolytes. A general method is presented for calculating the equilibrium inner potential difference between the two phases and equilibrium concentrations of redox species, as well as other ionic components from given initial concentrations, values of standard electrode potential of redox couples, and of standard ion transfer potential of other ionic components. The ion-electron exchange across the interface is exemplified for several simpler cases. The volume ratio has a dramatic effect on the equilibrium. The partition of indifferent-electrolyte ions can drive the redox reactions before the onset of electrolysis and can significantly alter the initial conditions for electron transfer studies at the liquid-liquid interface.     

应用标准电极电势求标准平衡常数的几个注意点

针对现行教材中由电极电势求化学反应平衡常数的计算公式缺少详细说明而易引起学生误会乱用的问题,本文分别从应用公式的前提条件、须与化学反应计量式相对应和应用公式的适当拓展等三个方面,以例题的形式逐一展开讨论,旨在帮助学生加深理解公式的内涵,提高准确应用知识解决实际问题的能力。     

硫化汞溶解机理的研究

根据热力学平衡原理和设计的可逆电池反应,由 E~0(Hg~(2+)+S/HgS)数据,计算了 E~0(HgCl_4~(2+)+S/HgS+4Cl~-)数值,将其与 HNO_3的标准电极电位比较,定量地揭示了 HgS 溶于王水的原因在于该溶液中高浓度 Cl~-离子降低了 HgS 中硫的还原电位,从而提高了 HgS 的还原性所致,并非王水的氧化性比 HNO_3的更强。根据这个机理,作者进一步对有关电极反应的电极电位进行了计算和分析,预测并经实验验证了多种可以溶解 HgS 的普通化学试剂。     

Electrochemical formation of Au2Na alloy and the characteristics of (Au2Na+Au) reference electrode in a LiF–NaF–KF eutectic melt

A cyclic voltammogram at a Au electrode in a LiF–NaF–KF eutectic melt at 773 K showed a cathodic peak at 0.45 V (vs. K⁺/K). XRD analysis of the electrode confirmed that the cathodic peak corresponded to the formation of Au₂Na alloy phase. The equilibrium potential of the reaction: 2Au+Na⁺+e⁻Au₂Na was determined to be 0.535 V at 773 K by open-circuit potentiometry at the Au–Na alloy electrode. The thermodynamic properties including the standard Gibbs free energy of formation were estimated for Au₂Na alloy at 773–860 K. The (Au₂Na+Au) electrode was proved to have excellent characteristics as a reference electrode in terms of reproducibility, stability and reversibility.     

Manganese dioxide-electrode at potentials at and close to the open circuit potential of the electrode

A thermodynamic treatment of the proton equilibrium shows that the electrode potential of the manganese dioxide-electrode referred to the hydrogen electrode in the same solution should be pH-independent. As this is not confirmed by the literature values of the electrode potential, a study of the electrode near the open circuit potential has been performed. The results have been treated by using a spherical model for diffusion in the electrode.     

Standard electrode potentials of the elements as a fundamental periodic property of atomic number

It is shown that the standard electrode potentials of the elements are a periodic property of the atomic number. The experimentally measured standard electrode potential of an element is related to fundamental elemental properties through a thermodynamic cycle. Metal atoms are first atomized to the vapor phase, are then ionized to form gaseous ions, and are then hydrated to form an ion-water cluster, which is next introduced into the aqueous solution. The standard electrode potential calculated from such a cycle is in good agreement with standard values for univalent, divalent and trivalent metal ions. It is shown that the periodicity in the standard electrode potential as a function of atomic number arises from the periodicity in the enthalpy term which is used to calculate standard electrode potentials from the equivalent thermodynamic cycle.     

Electrocatalytic dechlorination of a PCB congener at a palladized granular-graphite-packed electrode: Reaction equilibrium and mechanism

Our previous study on the electrocatalytic dechlorination of 2-chlorobiphenyl at a Pd-loaded granular graphite-packed electrode demonstrated that the process did not follow the first-order kinetics. The rate constant varied with the applied potential at the beginning, but later became irrelevant to the potential. The electrocatalytic kinetic was investigated in this study, in which several experiments were conducted to dechlorinate 2-chlorobiphenyl using a Pd-loaded granular graphite-packed electrode at different potentials and in methanol–water solutions. Analysis of the experimental results reveals that the electrocatalytic process had reached equilibrium in these experiments. The apparent equilibrium constants, as well as the rate constants for the overall forward and backward reactions, were related to the applied potential. These relationships follow the Tafel equation, but the apparent charge transfer coefficients are very small values. The potential dependence of the overall rate constants suggests a reaction mechanism in which the electrocatalytic reaction is the rate-determining step. The influence of methanol on (together with the potential dependence of) the overall rate constants and the apparent equilibrium constant suggests a Langmuir–Hinshelwood mechanism.     

Numerical computation of the Faradaic impedance of inlaid microdisk electrodes using a finite element method with anisotropic mesh adaptation

The Faradaic impedance of a microdisk electrode inlaid in an insulating surface is revisited by numerical computation using a finite element method (FEM) with anisotropic mesh adaptation. New features of the numerical results, as compared to previous works, are analyzed. A first attractive feature is that the diffusion impedance relative to a microdisk electrode, evaluated at the equilibrium potential of the electrode, depends both on electron-transfer and mass-transport kinetics, in contrast with the usual behaviour of uniformly accessible electrodes. Next, the domain of validity of the Fleishmann and Pons semi-analytical formulation of diffusion impedance is determined. Finally, the characteristic of impedance graphs, which are the diffusion resistance, the characteristic frequency at the apex of the Nyquist diagram and the imaginary part of the diffusion impedance at this apex, are studied as functions of a dimensionless parameter that compares the standard rate constant of electron transfer to the microelectrode diffusion constant. Closed form approximations are proposed for all quantities in order to help the analysis of experimental data.