第6章 化学动力学 (Chapter VI Chemical Kinetics),速度篇,引言,化学反应 (Chemical reaction),化学计量学 (stoichiometry),能量学 (energetics),速度学 (rate),对化学反应规律的认识？,The wide range of reaction rates.,引言,自发性速度快,化学反应的一个重要特征：自发性。,C (diamond) C (graphite),2H2 (g)+O2(g) 2H2O(l),3H2 (g)+N2(g) 2NH3 (g),有必要研究化学反应的速度!,化学动力学,例如：,Reaction rate: the central focus of chemical kinetics,Factors That Influence Reaction Rate,Under a specific set of conditions, every reaction has its own characteristic rate, which depends upon the chemical nature of the reactants.,Four factors can be controlled during the reaction: Concentration - molecules must collide to react; Physical state - molecules must mix to collide; Temperature - molecules must collide with enough energy to react; The use of a catalyst.,Collision energy and reaction rate.,(i) 研究各种因素，包括浓度、温度、催化剂、光照等对化学反应速率(reaction rate)影响的规律；,(ii) 研究一个化学反应过程经历哪些具体步骤，即所谓反应机理(或叫反应历程)(reaction mechanism)。,化学动力学的主要研究内容,例如,A+BAB,固相粉末反应,化学动力学的主要研究内容,催化反应(catalytic reactions),(a).Adsorption and activation of the reactants,(b).Migration of the absorbed reactants on the metal surface,(c).Reaction of the absorbed substances,(d).Escape, or desorption, of the products,例如,1850: Wilhelmy (Germany) studied the rate of inversion of sucrose (hydrolysis into D-(+)-glucose and D-(-)-fructose in the presence of an acid) and found it to be proportional to the concentrations of both the sugar and the acid. 1864: Guldberg and Waage (Norway) formulated their “law of mass action,“ according to which the reaction “forces“ are proportional to the product of the concentrations of the reactants: K=Rr Ss/(Aa Bb) where a, b, r and s are the stoichiometric coefficients in the chemical equation A+B=R+S. So the rate of the forward reaction is proportional to Aa Bb and that of the reverse reaction is proportional to Rr Ss.,The world of Physical Chemistry，by K. J. Laidler, Oxford Univ. Press, 1993,1884: vant Hoff (The Netherlands) published his “Studies of Chemical Dynamics“ (tudes de dynamique chimique) 1887: Ostwald (Germany) introduces the terms “reaction order“ and “half-life“. 1889: Arrhenius (Sweden) further analyzed the temperature dependence of reaction rate, k = A exp(-B/T), and gave it an “energy barrier“ interpretation; this is now called the “Arrhenius equation.“,The world of Physical Chemistry，by K. J. Laidler, Oxford Univ. Press, 1993,1913: Chapman (UK) introduced and Bodenstein (Germany) developed the steady-state approximation in chain reactions, according to which the rate of change of intermediate products is negligible. 1917: Trautz (Germany) and Lewis (UK) independently proposed that the rate of reaction is determined by the frequency of molecular collisions. This is now known as the “collision theory“ of chemical reaction kinetics. 1935: Eyring (USA) developed a statistical treatment called the “theory of absolute reaction rates“ or “transition state theory”.,The world of Physical Chemistry，by K. J. Laidler, Oxford Univ. Press, 1993,“for their contributions concerning the dynamics of chemical elementary processes“,The Nobel Prize in Chemistry 1986,Dudley R. Herschbach 1932 ,Yuan T. Lee 1936 ,John C. Polanyi 1929 ,准直孔,A分子束源,B分子束源,速度选择器,速度选择器,C,散射分子,分子束 作用区,移动检测器,交叉分子束实验装置示意图 （整个装置处于真空室内）,“for his contributions to the theory of electron transfer reactions in chemical systems“,The Nobel Prize in Chemistry 1992,R. A. Marcus,Electron Transfer Reactions in Chemistry: Theory and Experiment (Nobel Lecture) Angewandte Chemie 105, 1161 (1993） Summarizing Lecture: Quantum catalysis in enzymes - beyond the transition state theory paradigm， Philosophical Transactions Royal Society B, 361, 1445 (2006),The Nobel Prize in Chemistry 1999,Prof. Alhem Zewail,For his pioneering developments in,the field of femtoscience, making it,possible to observe the movement of,the individual atoms in a femtosecond。,基本概念,基元反应 (elementary reactions): 一步完成的反应。,单分子反应 双分子反应 三分子反应,I2 2I,Br + H2 HBr + H,2I + H2 2HI,基本概念,简单反应 (simple reactions) 复合反应 (complex reactions),总反应 (overall reactions),H2 + I2 2 HI,(1) I2 2I,(2) 2I + H2 2HI,引言小结,影响因素：浓度、温度、压力、外场等 反应机理 实验手段与理论的不断发展,反应速率规律的认识,6.1 反应速率方程(reaction rate equation),6.1.1 反应速率的表示方法,6.1.2 反应速率的测量方法,6.1.3 质量作用定律和速率方程 (Law of mass action and rate equation),化学反应: aA + bB gG + hH,6.1.1 反应速率的表示方法,反应的快慢：所需时间的长短,反应的规模：所占空间的大小,单位体积中反应进度随时间的变化率,定义反应速率：,国际单位: mol m-3 s-1,表示方法的优点：,6.1.1 反应速率的表示方法,强度性质 与反应物质选择无关,有时对于恒温气相反应，,6.1.1 反应速率的表示方法,对于体积不变的反应体系，,c t 曲线上的切线斜率,c t 曲线: 动力学曲线 (kinetic curve),6.1.2 反应速率的测量方法,例如：化学方法测定浓度变化,CH3COOC2H5 + NaOH CH3COONa + C2H5OH,化学滴定测定NaOH的消耗量。,6.1.2 反应速率的测量方法,用物理性质的变化通常来表征反应的进程：,例如：1) Wilhelmy 在1850年的实验,体积、压力、电导率、 pH、折射率、导热系数、极化率、光谱测定、旋光度等,C12H22O11 + H2O C12H22O11 + C12H22O11,蔗糖,葡萄糖,果糖,2) N2O5 = N2O4 + 0.5 O2,测定压力变化（等容下）.,6.1.2 反应速率的测量方法,反应速率与浓度有关。通常，反应速率与反应物浓度的适当方次成正比 :,k：反应速率系数 (rate coefficient). , 等:分级数 (partial order).,n = + + +:反应的总级数(overall order