PROFESSORDRWALTHERNERNST356.1054tnnaEMMANERNSTBEBLOHMEYERHILDECAHN GEB NERNSTNEOITHVONZANTHEERGEBNERNST52020OBELPRIS1920NERNSTSVERIGEGDR,1950Sweden,1980PostalstampsmemorizingNernst'sscientificachievements
1 GDR, 1950 Sweden, 1980 Postal stamps memorizing Nernst's scientific achievements
In1887NernstjoinedWilhelmOstwald at LeipzigUniversity,wherevan't Hoff and Arrhenius werealreadyestablished,and it wasinthisdistinguishedcompanyofphysical chemiststhatNernstbeganhis important researches.Nernst'searlystudiesinelectrochemistrywereinspiredbyArrhenius'dissociationtheorywhichfirstrecognized theimportance of ions in solution.In1889,heshowedhowthecharacteristics ofthecurrentproducedcouldbe usedtocalculatethe free energy change in the chemical reactionproducing the current.Nernst first explained theionizationofcertainsubstanceswhendissolvedinwater.Heconstructedaneguation,knownasthe Nernst Equation,whichrelated the voltageofacelltoitsproperties.IndependentlyofThomson,heexplainedwhycompoundsionizeeasily in water.The explanation,called theNernst-Thomsonrule,holdsthatitisdifficultforcharged ionsto attract each other throughinsulating water molecules,so they dissociate
2 In 1887 Nernst joined Wilhelm Ostwald at Leipzig University, where van't Hoff and Arrhenius were already established, and it was in this distinguished company of physical chemists that Nernst began his important researches. Nernst's early studies in electrochemistry were inspired by Arrhenius' dissociation theory which first recognized the importance of ions in solution. In 1889, he showed how the characteristics of the current produced could be used to calculate the free energy change in the chemical reaction producing the current. Nernst first explained the ionization of certain substances when dissolved in water. He constructed an equation, known as the Nernst Equation, which related the voltage of a cell to its properties. Independently of Thomson, he explained why compounds ionize easily in water. The explanation, called the Nernst-Thomson rule, holds that it is difficult for charged ions to attract each other through insulating water molecules, so they dissociate
GrazUniversity,1887(Standing,fromtheleft)WaltherNernst,FranzStreintz,SvanteArrhenius,Hiecke(sitting,fromthe left)Aulinger, Albert von Ettingshausen, LudwigBoltzmann,IgnazKlemencic,V.Hausmanninger
3 Graz University, 1887 (Standing, from the left) Walther Nernst, Franz Streintz, Svante Arrhenius, Hiecke, (sitting, from the left) Aulinger, Albert von Ettingshausen, Ludwig Boltzmann, Ignaz Klemencic, V. Hausmanninger
Chemical KineticsChapter 7Rate of Reaction化学动力学发展的三个阶段：1.十九世纪后半叶：宏观化学动力学阶段1863年，挪威化学家古德贝格和瓦格，质量作用定律；1889年，阿累尼乌斯定律；2.1900~1950，一碰撞理论、过渡态理论；链反应（自由基，用NMR法）3.1950年以后，微观化学动力学(microscopicchemicalkinetics)/分子反应动态学（molecularreactiondynamics）：在分子水平基元反应的微观历程来研究分子的一次碰撞行为中的变化
4 Chapter 7 Chemical Kinetics —— Rate of Reaction 化学动力学发展的三个阶段： 1. 十九世纪后半叶：宏观化学动力学阶段 1863年，挪威化学家古德贝格和瓦格，质量作用定律； 1889年, 阿累尼乌斯定律； 2. 1900~1950，——碰撞理论、过渡态理论；链反应 （自由基，用NMR法） 3.1950年以后，微观化学动力学(microscopic chemical kinetics) /分子反应动态学(molecular reaction dynamics)：在分子水平 来研究分子的一次碰撞行为中的变化，基元反应的微观历程
Aims to discuss three issues:1Definitions of reaction rate2 Factors affectingthe rate of areaction2-1 Concentration2-2Temperatures2-3Reactantstate（反应物之间接触情况）2-4Catalysts3Theory ofReactionRates3-1 Collision Theory3-2Activated ComplexTheory
5 Aims to discuss three issues: 1 Definitions of reaction rate 2 Factors affecting the rate of a reaction 2-1 Concentration 2-2 Temperatures 2-3 Reactant state(反应物之间接触情况) 2-4 Catalysts 3 Theory of Reaction Rates 3-1 Collision Theory 3-2 Activated Complex Theory
1. Definitions of reaction rate(1) Average ratesDefinition 1: r = △C/△t > 0, unit: molL-l.s-lFor example:N2 + 3 H, = 2NH03.01.0t = 0 (mol·L-l)0.40.82.4t =2s (molL-1)rn2 = - (0.8-1.0)/2 = 0.1(mol·L-1.s-1)rr2 = - (2.4-3.0)/2 = 0.3 (mol·L-1.s-l)rnH3 = 0.4/2 =0.2 (mol·L-1.s-l)That is, rn2 : IH2 : InH3=1: 3: 2rn2/1 = rg2/3 = rnH3/2
6 1. Definitions of reaction rate （1）Average rates Definition 1: r = ∆C/∆t > 0, unit：mol·L-1·s-1 For example: N2 + 3 H2 = 2NH3 t = 0 (mol·L-1 ) 1.0 3.0 0 t =2s (mol·L-1 ) 0.8 2.4 0.4 rN2 = - (0.8-1.0)/2 = 0.1(mol·L-1·s-1 ) rH2 = - (2.4-3.0)/2 = 0.3 (mol·L-1·s-1 ) rNH3 = 0.4/2 =0.2 (mol·L-1·s-1 ) That is , rN2 ： rH2 ：rNH3 = 1：3：2 rN2 /1 = rH2 /3 = rNH3 /2
Def.2r = △C/(V;△t)For a reactionaA+bB→gG+hH[A]1 △[B]1△[G]1 A[H]1 ratebh△t△t△t△tagVVGVVBHAbhag
7 For a reaction a A + b B → g G + h H a b g h t H t h G t g B t b A a rate A B G H = = = = = = = − = − 1 [ ] 1 [ ] 1 [ ] 1 [ ] Def.2 r = ∆C/(Vi ∆t)
(2)Instantaneousrates（瞬时速率）r = lim △C/ △tr = lim △C/ (v;△t)△t>0△t->02N,0,= 2N,04 +0c(N205)/(mol-L-10.20022.40.20Eoaooanon0.15016.80.10A0.100I1.20,120024003600480060000(t/s)0.0505.6c(N2O5)-t关系图N,O,0.000010002000300040005000600070008000)9000瞬时速率是浓度随时间的变化率Time (s)
8 (2) Instantaneous rates (瞬时速率) r = lim ∆C/ ∆t r = lim ∆C/ (Vi ∆t) ∆t→0 ∆t→0 2N2O5 = 2N2O4 +O2 瞬时速率是浓度随时间的变化率
Example7-1 At 40.00 C in carbon tetrachloride, dinitrogenpentoxide is decomposed to oxygen according to the followingequation: 2N,O,= 2N,O +O,. According to the data used to plotFigure 7-1A, 1.15mL of STP oxygen gas were formed in the first300s 7.42 m L of STP oxygen gas were formed in the first 3000s.(1) What is the average rate of formation of STP oxygen gasduring the first 3oos? What is the average rate of formation ofSTP oxygen gas during the first 3000s? (2)What is the initial rateofformationofSTPoxygen?(2200s.9.4mL)10.00(5.000.00Figure7-1A10000200030004000Time (s)
9 Example7-1 At 40.00 C in carbon tetrachloride, dinitrogen pentoxide is decomposed to oxygen according to the following equation: 2N2O5 = 2N2O4 +O2 . According to the data used to plot Figure 7-1A, 1.15mL of STP oxygen gas were formed in the first 300s, 7.42 m L of STP oxygen gas were formed in the first 3000s. (1) What is the average rate of formation of STP oxygen gas during the first 300s? What is the average rate of formation of STP oxygen gas during the first 3000s? (2)What is the initial rate of formation of STP oxygen? Figure 7-1A
Example7-1 At 40.00 C in carbon tetrachloride, dinitrogenpentoxide is decomposed to oxygen according to the followingequation: 2N,O,= 2N,O +O,. According to the data used to plotFigure 7-1A, 1.15mL of STP oxygen gas were formed in the first300s, 7.42 mL of STP oxygen gas were formed in the first 3000s.(1) What is the average rate of formation of STP oxygen gasduring the first 3oos? What is the average rate of formation ofSTP oxygen gas during the first 3000s? (2)What is the initial rateofformationof STPoxygen?SOLUTION(1)Average rate of formation of oxygen = 1.15mL/300s= 0.00383mL/s =3.83x10-3 mL/sAverage rate of formation of oxygen =7.42/3000 =2.47 ×10-3 (mL/s)(2) slope of the tangent = (9.4-0.0) /(2200-0)= 4.3 ×10-3 (mL/s)
10 Example7-1 At 40.00 C in carbon tetrachloride, dinitrogen pentoxide is decomposed to oxygen according to the following equation: 2N2O5 = 2N2O4 +O2 . According to the data used to plot Figure 7-1A, 1.15mL of STP oxygen gas were formed in the first 300s, 7.42 mL of STP oxygen gas were formed in the first 3000s. (1) What is the average rate of formation of STP oxygen gas during the first 300s? What is the average rate of formation of STP oxygen gas during the first 3000s? (2)What is the initial rate of formation of STP oxygen? SOLUTION (1)Average rate of formation of oxygen = 1.15mL/300s = 0.00383mL/s =3.8310-3 mL/s Average rate of formation of oxygen =7.42/3000 =2.47 10-3 (mL/s) (2) slope of the tangent = (9.4-0.0) /(2200-0) = 4.3 10-3 (mL/s)