2012年暑期西部高等学校物理化学课程及主管教学院长系主任培训班 以系统化知识为载体推进思路与方法教育 山东大学 张树永 2012年8月13日

在教学中要讲方法论，在准确讲解基本原理的同时，必须提炼出主要方法加以讲解，指导学生举一反三。 高盘良，科学方法教育与创新能力培养，中国大学教学，2010（3）：7-8

物理化学的教学目的： 让学生牢固掌握基本概念、基本原理、计算方法、实验方法、思维方法等物理化学基本内容和科学方法。 将化学的哲学和方法论基础、思维方法率先介绍给学生（授之以渔），启发学生在学习物理化学过程中学会质疑与思考、探索和创新，并为未来学习其他专业课程时提高思考水平和学习层次（识记、理解、应用、分析、综合、评价）奠定基础。 改革方法： 将知识点系统化,附之以素质和能力培养内容 知识不再是终极目标，而是素质和能力的载体。

《物理化学》中蕴含的科学方法 （1）线性化方法 （2）模型化方法 （3）相对基准方法 （4）因素综合法 （5）简化处理 （6）概念的演进 （7）科学语言与符号 （8）科研的基本思路

Kohlrausch empirical formula （1）线性化方法 Kohlrausch empirical formula Lewis empirical formula

Tafel empirical formula log j / A m-2 E / V 0.0 Tafel empirical formula Arrhenius empirical formula

(2) 模型化方法 在物理化学中模型化方法非常常见，如离子氛模型、分子碰撞模型、双电层结构模型、单分子层吸附模型、多分子层吸附模型、胶体粒子结构模型等。 模型化方法的主要目的一是提供一个比较清晰的物理图像，便于理解；一是通过简化便于进行数学物理处理。 以离子氛模型为例进行说明

Theoretical evaluation of Wr’ For ideal solution: For nonideal solution: Theoretical evaluation of Wr’ Before 1894: solution is taken as ideal gas 1918-1920: Ghosh – crystal structure 1923: Debye-Hückel: ionic atmosphere

+ Basic assumptions 1) Point charge 2) Only coulombic attraction 3) Dielectric constant keep unchanged 4) Boltzmann distribution, Poisson equation +  Shielded Coulombic potential + Debye length

Group exercise: Deduce Lewis’s empirical equation from

Model modification Valid for c < 0.1 mol·kg-1

Models of electric double layer 3) Stern double layer (1924) Holmholtz double layer (1853) 2) Gouy-Chappman layer (1910, 1913) +  d E +  d E +  d E Compact double layer Diffuse double layer

Cu(s)Zn(s)ZnSO4(m1)CuSO4(m2)Cu (s) （3）相对基准方法 相对性的方法和相对基准方法帮助他们打开了非常多的死结（deadlock），解决了非常多的问题。 Cu(s)Zn(s)ZnSO4(m1)CuSO4(m2)Cu (s) anode cathode E = c +  + j + + E = c + (l,1- ) + ( +- l,2) =  +-  + (c+  l,1-  l,2)

- NHE || unknown electrode + Normal/Standard Hydrogen Electrode (NHE/SHE) In 1953, IUPAC defined normal hydrogen electrode as the reference for measurement of electrode potential. IUPAC conventions pure hydrogen gas at standard pressure platinized platinum foil electrode acidic solution with activity of H+ equals to 1 definition  H+/H2 = 0.000000 V. - NHE || unknown electrode +

Thermodynamic quantities of ions How to solve this deadlock? The customary convention is to take the standard free energy of formation of H+(aq) at any temperatures to be zero.

Valence types and concentration （4）因素综合法 Valence types and concentration type electrolyte 0.1 m 0.2 m 1.0 m 1:1 RbNO3 0.734 0.658 0.430 NH4ClO4 0.730 0.660 0.482 1:2 BaCl2 0.508 0.450 0.401 CaCl2 0.510 0.457 0.419 1:3 LaCl3 0.314 0.274 0.342 FeCl3 0.325 0.280 0.270 平均活度系数受浓度和价型的影响，而且价型的影响更加显著。为了综合表示这两个因素的影响，Lewis提出离子强度（ionic strength, I）的概念。

Lewis, who noted that nonideality observed in electrolytic solutions primarily stems from the total concentration of charges present rather than from the chemical nature of the individual ionic species, introduced ionic strength in 1921. Valid when c < 0.01 m

(1) Steady-state approximation （5）简化处理 化学的研究对象通常比较复杂，特别对于描述大量物质宏观统计行为的物理化学，要通过简单方式描述体系的性质或者变化规律往往存在困难。 1）反应机理的简化处理 (1) Steady-state approximation (2) Rate-determining step (r. d. s.) approximation (3) Pre-equilibrium approximation

(1) Steady-state approximation k2/k1 1/5 5 10 100 103 108 tmax 2.01 0.40 0.25 0.047 710-3 10-7 ymax/a 0.67 0.13 0.08 7 10-3 10-3 Ea,1Ea,2 -0.4 4.0 5.7 11.5 17.2 46.1 t y k1/k2 When k2 >> k1, ymax would be very small, and the tmax would be very short.

Steady-state approximation Physical meaning of k2 >> k1 B is a active intermediate, it is difficult to form but easy to decompose to product. For consecutive reaction with large k2/k1 ratio, once the reaction take place, the active intermediate (B) rapidly attains its maximum concentration and its concentration keeps nearly unchanged during the whole reaction. Steady-state approximation

(2) Rate-determining step (r. d. s.) approximation When k2 >> k1 The total rate is determined mainly by k1 When k2 << k1 The total rate is determined mainly by k2 The rate of the overall consecutive reaction depends only on the smaller rate constant (rate-determining step).

rate-determining step (r. d. s.): the step with the slowest rate. ?? !!  It’s a r.d.s   patient !

（6）概念的演进 G   U U t t 宏观 微观 动态

（7）科学语言与符号 每个学科都有自己的语言系统。这些语言系统是由概念、定义和符号组成的。作为化学学科世界观和方法论集成的物理化学，其语言和符号也相对更复杂。 现通过几个实例来说明：     1）标准氢电极：Pt(s)H2(g, p)  H+ (a=1)     2) 铅酸蓄电池：Pb(s)  PbSO4(s)  H2SO4(aq)  PbSO4(s)  PbO2(s)  Pb(s)     3) Fe(OH)3溶胶：[(Fe(OH)3)m·nFeO+·(n-x)Cl-]x+ ·xCl-

（8）科研的基本思路 T k T k T k T k T k

Van’t Hoff’s Law The Arrhenius equation is a simple, but remarkably accurate, formula for the temperature dependence of the reaction rate constant, and therefore, rate of a chemical reaction. The equation was first proposed by the Dutch chemist J. H. van 't Hoff in 1884; five years later in 1889, the Swedish chemist Svante Arrhenius provided a physical justification and interpretation for it. Currently, it is best seen as an empirical relationship.[2]

Arrhenius extended the ideas of Vant’ Hoff and suggested a similar empirical equation. Defined the activation energy (Ea) The first definition of activation energy: experimental activation energy

ClCOOCH3 + H2O  CO2 + CH3OH + H+ + Cl T / K 273.72 278.18 283.18 288.14 104 k / s-1 0.4209 0.7016 1.229 2.087 298.18 308.16 318.29 5.642 14.05 32.65 R = 0.99992 Ea = 70.80 kJ mol-1, A =1.32  109