化学专业英语ReactionRate.pptx

《化学专业英语ReactionRate.pptx》由会员分享，可在线阅读，更多相关《化学专业英语ReactionRate.pptx（44页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、(1)The entropy of phase transition at Ttrs , ReversibleAt the normal transition temperature, Ttrs, any transfer of heat between the system and its surroundings is reversible because the two phases in the system are in equilibrium. HqtrsSince at constant p, the change in molar entropy of the system i

2、s trstrstrsTHSH2O(s) 1 mol273K1 atmH2O(l) 1 mol273K1 atmreversibleStrstrstrsTHSAt Ttrs =273K(2) The entropy of transition at T , IrreversibleIf a process changes at which the temperature deviates the normal transition temperature, Ttrs, the process is not a reversible and the above equation can not

3、be directly used to calculate the change in entropy.In this caseAt T=263K(TTtrs)H2O(l) 1 mol263K1 atmirreversibleH2O(l) 1 mol273K1 atmH2O(s) 1 mol273K1 atmreversibleSS1S3S2H2O(s) 1 mol263K1 atmS=S1 +S2 +S3At T=263K(TTtrs)H2O(l) 1 mol263K1 atmirreversibleH2O(l) 1 mol273K1 atmH2O(s) 1 mol273K1 atmreve

4、rsibleSS1S3S2H2O(s) 1 mol263K1 atmH2O(s) 1 mol273K1 atmH2O(l) 1 mol273K1 atmreversibleStrstrstrsTHSS=S1 +S2 +S3The entropy of phase transitionsThe measurement of entropy form heat capacityThe entropy of a system at a temperature T based on its entropy at T = 0ffus0f(s)d(0)(THTTCSTSTpTpTpTTCTHTTCbbfT

5、bvapTd)g(d) l (The entropy is equal to the area beneath the upper curve up to the corresponding temperature, plus the entropy of each phase transition passed. Debye extrapolation Theoretically, the heat capacity is proportional to T 3 when T is low: Cp = aT 3The variation of Cp/T with the temperatur

6、e The measurement of entropy form heat capacityThe Third Law of thermodynamicsThe entropy change accompanying any physical or chemical transformation approaches zero as the temperature approaches zero:The Nernst heat theoremS T 0 K = 0The Third Law thermodynamicsIf the entropy of every element in it

7、s most stable state at T=0 is taken as zero, then every substance has a positive entropy which at T=0 may become zero, and which does become zero for all perfect crystalline substances, including compounds.S(0K) = 0, for all perfect crystalline substancesThe Third Law does not state that entropies a

8、re zero at T = 0; it merely implies that all perfect materials have the same entropy at that temperature. Choosing this common value as zero is then a matter of convenience. Third-Law entropies The Third-Law entropy, standard entropy, :)( TSOn the basis of S(0K) = 0 for all perfect crystals, the ent

9、ropy of the substance in its standard state at the Temperature T is denoted )( TSThe standard reaction entropy, : the difference between the molar entropies of the pure, separated products and the pure, separated reactants, all substances being in their standard states at the specified temperature.S

10、rmReactantsmProductsr SSS (J) mJJrSS v-stoichiometric coefficient The Third-Law entropy, standard entropy, :)( TSTTCKSTSTSTpd)B()298,B(),B()(298m,BmBmBmr ),B()(mfBmrTSTS notice：),B(),B(mmfTSTS Stable elements： ，but0),B(mfTS0),B(m TSTo calculate standard reaction entropy from standard entropy The Thi

11、rd-Law entropy, standard entropy, :)( TSTi-Al 二元系相图二元系相图H2O的平衡相图的平衡相图的平衡相图的平衡相图过冷现象过冷现象S.Liquid Liquid & solidCrystallization begins 0o 1876 phase rule (Gibbs) 1900 construction of Fe-C phase diagram (H.W.Bakhius.Roozeboom) 1901-1925 heterogeneous equilibria (G. Tammann) 1930- X-ray diffraction meth

12、od introduced in crystal structure analysis 1970- Calculation of Phase DiagramHistoryPhase Equilibrium相平衡是热力学在化学领域中的重要应用之一相平衡是热力学在化学领域中的重要应用之一. .相图（相图（phase diagram） 表达多相系统的状态如何随温度、压力、组成等强表达多相系统的状态如何随温度、压力、组成等强度性质变化而变化的图形，称为相图。度性质变化而变化的图形，称为相图。材料工作者的地图材料工作者的地图 Thomas H. Adair, Professor, University

13、of MississippiPublish or Perish? “There are three necessary steps in useful research: the first to begin it, the second to end it and the third to publish it.” M. Faraday nSimple straightforward titleProtein association studied by NMR diffusometry Current Opinion in Colloid & Interface Science Volum

14、e 11, Issue 1 , April 2006, Pages 19-23 nTwo-part titleBiosynthesis of the Terpene Phenalinolactone in Streptomyces sp. T6071: Analysis of the Gene Cluster and Generation of erivatives Chemistry and Biology Volume 13, Issue 4 April 2006, Pages 343-460 Your paper is worthless if no one reads, uses, o

15、r cites it “A research study is meaningful only if someone else uses it in his/her studies. For this to happen a paper has to be written in a way that arouses other scientists interest and allows others to reproduce the results. Only an understandable study can be reproduced. Only a reproducible wor

16、k enables others to follow the lead. The number of scientists following the lead is a measure of the impact of a research study. Thus, in a way, a research study has to make a sale to other scientists.” ZHOU Yaoqi, Professor. Indiana University School of Informatics, IUPUI Even high impact factor jo

17、urnals have articles that get no citation or very low downloadsArticles with low downloadsSelection from the Full-text usage report: Cell, articles published in 2005 (2007.6)ExampleNon-cited papers in high IF journalsCitations of the Articles published in Cell at the year of 2005. (2007.6)ExampleEdi

18、tors now regularly analyze citations per article. “The statistic that 27% of our papers were not cited in 5 years was disconcerting. It certainly indicates that it is important to maintain high standards when accepting papers. nothing would have been lost except the CVs of those authors would have b

19、een shorter” Marv Bauer, Editor, Remote Sensing of EnvironmentArticles will increasingly be checked on originality and relevance. Acceptance will get even harder. Journal publishers do not want zero-cited articlesA journal is the gateway to a COMMUNITY of researchers with a common interest.nJournals

20、 are the prime carrier of scholarly communication. nNew research relies on relevant informationnJournal Editors + Reviewers + Authors + Readers A community of scientistsYou paper is your passport to your community The Rates of Chemical Reactions IntroductionIn this chapter we look into chemical reac

21、tion occur. The principal aspect we examine is the rate of a reaction, and we shall see how it depends on the temperature and the concentrations of the species that are present. There are two main reasons for studying the rates of reactions. The first is the practical importance of being able to pre

22、dict how quickly a reaction mixture will move its equilibrium state: the rate might depend on a number of factors under our control, such as temperature, the pressure and the presence of a catalyst, and, depending on our aims, we may be able to make the reaction proceed at an optimum rate.The second

23、 reason for studying reaction rates is that the study of rates can reveal the mechanism of reactions. The term mechanism has two connotations in this context. The term mechanism has two connotations in this context.The first is the analysis of a chemical reaction into a sequenceOf elementary steps.

24、The statement of all the elementary stepsConstitutes the statement of the mechanism of the reaction.The other meaning of mechanism relates to the individual steps themselves, and concerns their detailed nature. In this sense mechanism concerns what happens as a bromine atom approaches and attacks a

25、rotating, vibrating, hydrogen molecule. The first type of analysis of mechanism is the central feature of classical chemical kinetics and we concentrate on it in this chapter. The second type of analysis, called chemical dynamics, had to wait the technological advances that made available molecular

26、beams for the study of individual molecular collision, and is discussed in the next chapter.The dividing line between chemical kinetics and chemical dynamics is not clear cut: crude models of individual reaction steps were built on the basis of kinetic analyses, and we see something of this in the p

27、resent chapter. Empirical chemical kineticsThe basic data of chemical kinetics are the concentrations of the reactants and products as functions of time. The method selected for monitoring the concentrations depends on the nature of the species involved in the reaction, and on its rapidity.Many reac

28、tions go to completion (that is, attain thermodynamic equilibrium) over a period of minutes of hours, and may be monitored by classical techniques. One of the following methods of often chosen.1. Pressure changes 2. Spectroscopy 光谱学3. Polarimetry 旋光分析4. Electrochemical methods 电化学分析法5. Miscellaneous

29、 methods其他的分析法 Pressure changesA reaction in the gas phase might result in a change of pressure, and so its progress may be monitored by recording the pressure as a function of time. An instance of this is the decomposition of nitrogen oxide, according toFor every mole of N2O5 destroyed, 5/2 moles o

30、f gaseous products are formed, and so the pressure of the system increases during the course of the reaction. This method is inappropriate for reactions that leave the overall pressure unchanged, and for reactions in solution2N2O5(g) 4NO2(g) + O2(g) What is Spectroscopy?Spectroscopy pertains to the

31、dispersion of an objects light into its component colors (i.e. energies). By performing this dissection and analysis of an objects light, astronomers can infer the physical properties of that object (such as temperature, mass, luminosity and composition). The Electromagnetic SpectrumPhysicists class

32、ify light waves by their energies (wavelengths). Labeled in increasing energy, we might draw the entire electromagnetic spectrum as shown in the figure below: The Electromagnetic Spectrum. Notice how small the visible region of the spectrum is, compared to the entire range of wavelengths. What is Sp

33、ectroscopy?Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiat

34、ive energy as a function of its wavelength or frequency. Spectroscopic data is often represented by a spectrum, a plot of the response of interest as a function of wavelength or frequency. The Electrochemical methods When a reaction changes the number or nature of ions present in a solution, its cou

35、rse may be followed by monitoring the conductivity of the solution.One very important class of reactions consists of those occurring at electrodes, and we examine them in Chapter 30 The Electrochemical reaction If a chemical reaction is driven by an external applied voltage, as in electrolysis, or i

36、f a voltage is created by a chemical reaction as in a battery, it is an electrochemical reaction. In contrast, chemical reactions where electrons are transferred between molecules are called oxidation/reduction (redox) reactions. In general, electrochemistry deals with situations where oxidation and

37、 reduction reactions are separated in space or time, connected by an external electric circuit. Miscellaneous methodsOther methods of determining composition include mass spectrometry and chromatography. In order to employ these techniques, a small amount of the reaction mixture is bled from the reacting system at a series of times after the initiation of the reaction, and then analysed.