物理化学电子教案—第二章(下)课件

上一内容下一内容回主目录物理化学电子教案第二章（下）2024/7/6上一内容下一内容回主目录Adiabatic process In Fig.PV:Slope in AB：Slope in AC：In reversible process the work done （below the line AB）is big than the work done(below the line AC)in adiabatic reversible process.T2024/7/6上一内容下一内容回主目录Fig.adiabatic and isothermal rev.processIn an isothermal expansion heat continuously flows into the system,and so the pressure does not fall as much as in a thermally isolated,adiabatic expansion.2024/7/6上一内容下一内容回主目录 Work in adiabatic process（1）work in pg.a.r.process.thereforebecause2024/7/6上一内容下一内容回主目录A better calculation method（2）another way to calculate This equation is true for all adiabatic expansions or contractions involving a perfect gas or not,reversible or not.2024/7/6上一内容下一内容回主目录2.7 real gasJoule-Thomson experiment Joule在1843年所做的气体自由膨胀实验是不够精确的，1852年Joule和Thomson 设计了新的实验，称为throttling process。在这个实验中，使人们对实际气体的U和H的性质有所了解，并且在获得低温和气体液化工业中有重要应用。2024/7/6上一内容下一内容回主目录throttling processThe Joule-Thomson expansion consists of allowing a gas to expand through a porous plug from a region of higher pressure to a region of lower pressure as depicted in Fig.The process is carried out steadily and adiabatically.2024/7/6上一内容下一内容回主目录throttling processWhen the flow is sufficiently slow,the gas has well defined pressure and temperature on both sides of the restriction.2024/7/6上一内容下一内容回主目录U and H in the throttling processLeft,Surroundings compresses gaseous system:work,system got：Adiabatic Q=0，then：Right,gaseous system expansion：work,surr.got:2024/7/6上一内容下一内容回主目录U and H in the throttling processthe sum of work:thenThrottling process is const.-enthalpy process!It is isenthalpic.2024/7/6上一内容下一内容回主目录Joule-Thomson coefficient：0 经节流膨胀后，气体温度降低。-The isenthalpic J-T coefficient 是系统的强度性质。因为节流过程的 ,所以当：0 经节流膨胀后，气体温度升高。=0 经节流膨胀后，气体温度不变。2024/7/6上一内容下一内容回主目录Extent of reaction 20世纪初比利时的Dekonder引进反应进度 的定义为：单位：mol is the stoichiometric coefficient of component B,negative-reactants and positive-products.2024/7/6上一内容下一内容回主目录extent of reaction 引入反应进度的优点：在反应进行到任意时刻，可以用任一反应物或生成物来表示反应进行的程度，所得的值都是相同的，即：d=2024/7/6上一内容下一内容回主目录If the transfer of heat occurs at constant volume,and if no other forms of work are permitted,(U)v=Qv.For a specified change of state U is independent of how the change is brought about,therefore the subscript v can be dropped from U:U=Qv.The significance of this equation is that if we measure the heat transferred at constant volume we can identify it with the change in a thermodynamic state function.The reaction enthalpy2024/7/6上一内容下一内容回主目录The analogous result for changes occurring at constant pressure.H=Qp.When there is no work other than PV-work.The relation between H and U.The enthalpy of a substance differs from its thermodynamic energy by an amount pV.It follows that H=U+pV(products)-pV(reactants)For reactions involving only solids and liquids:H U 2024/7/6上一内容下一内容回主目录The relation between Qp and Qv When the extent of reaction is unity:or 2024/7/6上一内容下一内容回主目录Const.-p and const.-V heat of reactionreactantsproducts（3）（2)cons.V and products Deduce the relation between2024/7/6上一内容下一内容回主目录The heat at cons.volume and cons.pressure反应物生成物（3）（2）等容 生成物 For pg，P2V1-P1V1=P1V2-P1V1 2024/7/6上一内容下一内容回主目录The equation of thermochemistry U ,H are state functions，所以方程式中应该注明物态、温度、压力、组成等。对于固态还应注明结晶状态。例如：298.15 K时 式中：表示反应物和生成物都处于标准态时，在298.15 K，反应进度为1 mol 时的焓变。p代表气体的压力处于标准态。2024/7/6上一内容下一内容回主目录The standard molar enthalpy of reactionEnthalpy changeAll products and reactants being in their standard states at the TExtent of reaction is 1 molreactionReaction temperature2024/7/6上一内容下一内容回主目录压力的标准态 随着学科的发展，压力的标准态有不同的规定：标准态用符号“”表示，表示压力标准态。最老的标准态为 1 atm1985年GB规定为 101.325 kPa1993年GB规定为 1105 Pa。标准态的变更对凝聚态影响不大，但对气体的热力学数据有影响，要使用相应的热力学数据表。2024/7/6上一内容下一内容回主目录压力的标准态气体的标准态：压力为 的理想气体，是假想态。固体、液体的标准态：压力为 的纯固体或纯液体。标准态不规定温度，每个温度都有一个标准态。一般298.15 K时的标准态数据有表可查。为方便起见，298.15 K用符号 表示。2024/7/6上一内容下一内容回主目录2.9 Hesss law of constant heat summation1840年，根据大量的实验事实赫斯提出了一个定律：反应热只与起始和终了状态有关，与变化途径无关。不管反应是一步完成的，还是分几步完成的，其热相同，当然要保持反应条件（如温度、压力等）不变。It states that the standard enthalpy change in any reaction can be expressed as the sum of the standard enthalpy changes,at the same temperature,of a series of reactions into which the overall reaction may formally be divided.2024/7/6上一内容下一内容回主目录赫斯定律例如：求C(s)和 生成CO(g)的反应热。已知：（1）（2）则（1）-（2）得（3）（3）2024/7/6上一内容下一内容回主目录Enthalpy of formation of a compound没有规定温度，一般298.15 K时的数据有表可查。生成焓仅是个相对值，相对于稳定单质的焓值等于零。standard molar enthalpy of formationThe enthalpy changes that occur when unit amount of the compound in its standard state is formed from its elements in their standard states：（物质，相态，温度）2024/7/6上一内容下一内容回主目录Enthalpies of formation of compoundsFor example：at 298.15 KThis is the standard molar enthalpy of formation of HCl(g)：Reaction enthalpy：2024/7/6上一内容下一内容回主目录Define the reaction enthalpy is the stoichiometric coefficient,the negative sign going with the reactant and the positive with the product.The standard enthalpy of reactionis the difference H(products)-H(reactants),all substances being in their standard states at the temperature T.2024/7/6上一内容下一内容回主目录Enthalpy of combustionThe subscript“c”denotes combustion。The superscript“”denotes all substances being at standard pressure.The subscript“m”denotes the being 1 mol.At standard pressure and reaction temperature，the change of enthalpy accompanying total oxidation of a material is called Standard molar enthalpy of combustion.It is denoted(substance,phase,temperature)2024/7/6上一内容下一内容回主目录燃烧焓指定产物通常规定为：金属 游离态显然，规定的指定产物不同，焓变值也不同，查表时应注意。298.15 K时的燃烧焓值有表可查。2024/7/6上一内容下一内容回主目录燃烧焓例如：在298.15 K及标准压力下：则 显然，根据标准摩尔燃烧焓的定义，所指定产物如等的标准摩尔燃烧焓，在任何温度T时，其值均为零。2024/7/6上一内容下一内容回主目录Use of the enthalpy of combustion例如：在298.15 K和标准压力下，有反应：（A）（B）（C）(D)则The reaction enthalpy is given by：in calculating the enthalpy of a reaction.2024/7/6上一内容下一内容回主目录Calculate the enthalpy of formation该反应的反应焓变就是 的生成焓，则：例如：在298.15 K和标准压力下：using enthalpies of combustion.2024/7/6上一内容下一内容回主目录Kirchhoffs law1858年Kirchhoff提出了 The temperature dependence of reaction enthalpies 也是温度的函数，只要将Cp-T的关系式代入，就可从一个温度时的焓变求另一个温度下的焓变。如有物质发生相变，就要进行分段积分。2024/7/6上一内容下一内容回主目录Adiabatic reaction求终态温度的示意图 设反应物起始温度均为T1，产物温度为T2，整个过程保持压力不变：2024/7/6上一内容下一内容回主目录2.12 绝热反应根据状态函数的性质可由 表值计算可求出从而可求出T2值2024/7/6上一内容下一内容回主目录Phase transitionsDuring a change of phase of a pure substance,such as vaporization,melting,and sublimation,its temperature and pressure remain constant while its entropy and volume undergo changes.The temperature and pressure of a pure substance consisting of two phases in equilibrium are not independent variables.2024/7/6上一内容下一内容回主目录Reversible phase transitionslgP*TH2O(l)H2O(g)T,P*enthalpy of phase transitionvap Hmenthalpy vaporizationQp=vap Hm=Qr2024/7/6上一内容下一内容回主目录The temperature dependence of enthalpy H2O(l)H2O(g)H2O(l)H2O(g)T2,P*2T1,P*1vap Hm,2=vap Hm,1+Take it as const.P The end2024/7/6上一内容下一内容回主目录JAMES PRESCOTT JOULEJAMES PRESCOTT JOULE(1818-1889)English physicist,had the strength of mind to put science ahead of beer.He owned a large brewery but neglected its management to devote himself to scientific research.His name is associated with Joules law,which states that the rate at which heat is dissipated by a resistor is given by I2R.He was the first to carry out precise measurements of the mechanical equivalent of heat;and the firmly established that work can be quantitatively converted heat.2024/7/6上一内容下一内容回主目录JOSEPH LOUIS GAY-LUSSACJOSEPH LOUIS GAY-LUSSAC(1778-1850)French chemist,was a pioneer in balloon ascensions.In 1804,Gay-Lussac made several balloon ascensions to altitudes as high as 7000 m,where he made observations on magnetism,temperature,humidity,and the composition of air.He could not find any variation of compositions with height.In 1809,he pointed out that gases combine in simple proportions by volume;and this is still called Gay-Lussacs work on chlorine brought the scientist into controversy with Sir Humphry Davy.2024/7/6上一内容下一内容回主目录JOSEPH LOUIS GAY-LUSSACGay-Lussac assumed chlorine to be an oxygen-containing compound,while Davy correctly considered it an element,a view that Gay-Lussac eventually accepted.He showed that prussic acid contained hydrogen but no oxygen.Lavoisier had insisted that oxygen was the critical constituent of acids,and Gay-Lussac.Gay-Lussac was one of the tubing,all of which had to be imported from German,and the French had an import duty on glass tubing.He instructed his German supplier to seal both ends of each piece of tubing and label the tubes“German air.”The French government had no duty listed for“German air”,and he was able to import his tubing duty free.2024/7/6上一内容下一内容回主目录WILLIAM THOMSON,Lord Kelvin WILLIAM THOMSON,Lord Kelvin(1824-1907)Irish-born British physicist,proposed his absolute scale of temperature,which is independent of the thermometric substance in 1848.In one of his earliest papers dealing with heat conduction of the earth,Thomson showed that about 100 million years ago,the physical condition of the earth must have been quite different from that of today.He did fundamental work in telegraphy,and navigation.For his services in trans-Atlantic telegraphy,Thomson was raised to the peerage,with the title Baron Kelvin of Larg.There was no heir to the title,and it is now extinct.2024/7/6上一内容下一内容回主目录HESS HESS(1802-1852)俄国化学家，1802年出生于德国。在1836年提出了著名的赫斯定律。赫斯定律是热化学的最基本规律。根据这个定律，热化学公式可以互相加减，从一些反应的反应热可求出另一些反应的反应热。这个定律的发现以及当时所采用的实验方法，为以后热力学第一定律的确立奠定了实验基础。2024/7/6上一内容下一内容回主目录LINUS CARL PAULINGLINUS CARL PAULING(born 1901)American chemist,did his earliest work in crystal structure determinations,using X-ray diffraction.The early years of his career coincided with the development of quantum mechanics,and his interest in structural chemistry led him to a variety of quantum mechanical investigations concerned with the solid and nonsolid states of matter.After the war,his interests turned partly to biochemistry,and Pauling discovered the cause of sickle-cell anemia.2024/7/6上一内容下一内容回主目录LINUS CARL PAULINGHe received the Nobel Prize in chemistry in 1954 for his research into the natrue of the chemical bond and the structure of complex molecules.In the late 1950s and early 1960s,he was one of the most vocal opponents of atomic bomb testing,and received the Nobel Peace Prize in 1963 for his efforts on behalf of the nuclear ban treaty,thereby becoming the only person to win two individual Nobel awards.2024/7/6上一内容下一内容回主目录KIRCHHOFF,GUSTER ROBERTKIRCHHOFF,GUSTER ROBERT(1824-1887)德国物理化学家。1858年发表了著名的基尔霍夫定律。该定律描述了反应的等压热效应和温度之间的关系。根据基尔霍夫公式，可以从一个温度时的反应热求得另一个温度时的反应热。2024/7/6