物理化學英文課件：chapter05 Standard Thermodynamic Functions of Reaction

1、Chapter 5Standard Thermodynamic Functions of ReactionChapter 5Physical ChemistryStandard States of Pure SubstancesStandard stateP 1 bar Gas: P = 1 bar, T, gas idealThe standard-state pressure is denoted by Po:Po 1 bar, T Solid or liquid：P 1 bar, TThe standard state of a substance at a specified temp

2、erature is its pure form at 1 bar.Standard Thermodynamic Functions of ReactionPhysical ChemistryChapter 5Standard Enthalpy of ReactionFor a chemical reactionThen aA + bB cC + dDMolar enthalpy of substance (C) in standard state at TStandard enthalpy (change) of reaction (Sometime, is used for ) For t

3、he general reaction (Eq. (4.94)(5.3)*Physical ChemistryChapter 5Standard Enthalpy of ReactionFor exampleThen Ho depends on how the reaction is written2 C6H6 (l) + 15 O2 (g) 12 CO2 (g) + 6 H2O (l)C6H6 (l) + 7.5 O2 (g) 6 CO2 (g) + 3 H2O (l)Physical ChemistryChapter 5Standard Enthalpy of FormationThe r

4、eference form (reference phase) of an element at T is usually taken as the form of the element that is most stable at T and 1-bar pressure.For example, for H2CO(g) at 307 KC (graphite, 307 K, Po )H2 (ideal gas, 307 K, Po)O2 (ideal gas, 307 K, Po ) H2CO (ideal gas, 307 K, Po)For an element in its ref

5、erence form, is zero.For example, 0。C (graphite, 307 K, Po ) C (diamond, 307 K, Po) C (graphite, 307 K, Po ) C (graphite, 307 K, Po)Nothing happens in this “process”however, ( )Physical ChemistryChapter 5Consider the reaction aAb B cCdDThe standard enthalpy change for a chemical reaction(5.6)*Reacta

6、nts aA + bBin their standard states at TProducts cC + dDin their standard states at TElementsin their standard states at T(1)(2)(3)Fig. 5.1Physical ChemistryChapter 5a Ab B c Cd D+)Reactants aA + bBin their standard states at TProducts cC + dDin their standard states at TElementsin their standard st

7、ates at T(1)(2)(3)Fig. 5.1Physical ChemistryChapter 5Determination of f Ho and r Ho Read page 144Use calorimetryWhen a reaction is carried out in a calorimeterThe heat lost/gainedby the reacting systemThe heat gained/lostby the calorimeter and its contents=Changes in heat content are calculated usin

8、gPhysical ChemistryChapter 5Enthalpies of combustion are measured in a bomb calorimeter.H2OO2 (g)Sample pelletStirrerElectrical heaterThermometer Ignition wiresFig. 5.4Adiabatic wallPhysical ChemistryChapter 5Thermochemistry The study of the heat produced or required by chemical reactionsCalorimetet

9、ry Heat produced /adsorbed by a reactionq = U (const. V)q = H (const. P)Physical ChemistryChapter 5Enthalpies of transitionTransitionProcess Symbol Transition FusionVaporizationSublimationMixing of fluidsSolutionHydrationAtomization Phase Phase sl lg sgPure mixtureSolutesolutionX(g)X(aq)Species(s,l,

10、g)atoms(g)trsHfusHvapHsubHmixHsolHhydHatHEnthalpies of physical changePhysical ChemistryChapter 5Enthalpies of transitionTransitionProcess Symbol Transition Ionization Electron gainReaction Combustion Formation Activation Phase Phase X (g)X+(g)+e-(g) X (g)+e-(g)X-(g) ReactantsproductsCompound(s,l,g)

11、+O2(g) CO2(g),H2O(l,g)ElementscompoundReactantsactivated complextrsHionHegHrHcHfHHPhysical ChemistryChapter 5Standard enthalpy of vaporizationThe enthalpy change per mole when a pure liquid at 1 bar vaporizes to a gas at 1 barH2O(l) H2O(g)Standard enthalpy of fusionThe enthalpy change accompanying t

12、he conversion of a solid to a liquidH2O(s) H2O(l)Enthalpies of physical changePhysical ChemistryChapter 5Standard enthalpy of sublimationThe standard enthalpy for a process in which a solid is converted directly into a vapor. C(s,graphite) C(g)Standard enthalpy of solutionThe standard enthalpy chang

13、e when it dissolves in a specified quantity of solvent.HCl(g) HCl(aq)Enthalpies of physical changePhysical ChemistryChapter 5Enthalpy of ionizationThe standard enthalpy change per mole for the removal of an electron from a species in the gas phase. Na(g) Na+(g) + e-(g)Electron gain enthalpyThe stand

14、ard enthalpy change accompanying electron attachment to an atom, ion, or molecule in the gas phase.Cl(g)+e-(g) Cl-(g)Enthalpies of physical changePhysical ChemistryChapter 5Bond dissociation enthalpyThe standard reaction enthalpy for the breaking of the A B bond.AB(g) A(g) + B(g)Enthalpy of atomizat

15、ionThe standard enthalpy change accompanying the separation of all the atoms in a substance (an element or a compound).Na(s) Na(g)Enthalpies of TransitionCH3OH(g) CH3(g) + OH(g)Physical ChemistryChapter 5Standard reaction enthalpyThe change in enthalpy when reactants in their standard states change

16、to products in their standard states.CH4(g) + 2O2(g) CO2(g) + 2H2O(l)Standard enthalpy of combustionThe standard reaction enthalpy for the complete oxidation of an organic compound to CO2 and H2O if the compound contains C, H, and O, and to N2 if N is also present.Enthalpies of chemical changeC6H12O

17、6(g) + 6O2(g) 6CO2(g) + 6H2O(l)Physical ChemistryChapter 5CH2=CH2(g) + H2(g) CH3 CH3(g)Standard enthalpy of hydrogenationThe standard reaction enthalpy for the hydrogenation of an unsaturated organic compound (with the compound ascribed the stoichiometric number 1 in the chemical equation).Enthalpie

18、s of chemical change + 3H2(g) Hydrogenation of etheneHydrogenation of benzenePhysical ChemistryChapter 5Relation between Ho and Uo(5.9)(constant P)(5.3)*Physical ChemistryChapter 5Relation between Ho and Uo(5.10)For example(5.9) C D BPhysical ChemistryChapter 5Relation between Ho and Uo(5.10)For rea

19、ctions not involving gases, ng=0, Ho = UoFor reactions involving gases, ng 0, Ho UoRT (kJ/mol) ngT=300K2.5small integerT=1000K8.3small integerVery smallHo UoPhysical ChemistryChapter 5Hesss LawThe overall enthalpy change for a reaction is equal to the sum of the enthalpy changes for the individual s

20、teps in the reaction measured at the same temperature.The enthalpy change in a chemical reaction depends only on the initial and final states and is independent of the reaction pathway.Standard enthalpies of individual reactions can be combined to obtain the enthalpy of another reaction. The applica

21、tion of the First Law is widely called Hesss law.Physical ChemistryChapter 5Temperature dependence of reaction heats(5.18)(4.30)The molar heat capacity of substance i in its standard state at the temperature of interest.Physical ChemistryChapter 5Temperature dependence of reaction heats(5.18)Integra

22、tion of (5.18) between T1 and T2 gives(5.19)Physical ChemistryChapter 5Temperature dependence of reaction heats(5.19)Kirchhoffs LawOver a short temperature range,(5.29)Temperature variation of standard-state molar heat capacityPhysical ChemistryChapter 5Example: Using Kirchhoffs lawThe standard enth

23、alpy of formation of gaseous H2O at 25 oC is 241.82 kJ/mol. Estimate its value at 100 oC given the following values of the molar heat capacities at constant pressure (assume that the heat capacities are independent of temperature):H2O(g)33.58 J/K molH2(g)28.84 J/K molO2(g)29.37 J/K molMethod. If CP

24、is independent of temperature in the range T1 to T2, thenWrite the chemical reaction, identify the stoichiometric numbers, and calculate Cp from the data.Physical ChemistryChapter 5Example: Using Kirchhoffs lawAnswer. The reaction isIt then follows thatPhysical ChemistryChapter 5Conventional Entropi

25、es and the Their LawThe second law:Method. Arbitrary set the molar entropy Sm for each element in this state is equal to zero.Measure the entropy changes (no absolute entropies)Assign an arbitrary entropy value to each element in a chosen reference stateFind S for the change from elements in their r

26、eference states to the desired substance in its standard state(5.22)*element in stable condensed formPhysical ChemistryChapter 5Conventional Entropies and the Their LawThe standard pressure of 1 bar and a temperature of absolute zeroConventional entropy of a compound. The use of limit indicates that

27、 absolute zero is unattainable.(5.22)*Table of Conventional enthalpies (enthalpies of formation)(3.30)Conventional entropy of an elementPhysical ChemistryChapter 5The Third Law of ThermodynamicsThe slope of the Go-versus-T curve for a reaction goes to zero as T goes to absolute zero.(5.23)(4.51)Conv

28、entional entropy of an elementS for a chemical reaction is not easily measured.(5.24)Physical ChemistryChapter 5The Third Law of ThermodynamicsFor any isothermal process that involves only substances in internal equilibrium, the entropy change goes to zero as T goes to zero.Nernst-Simon Statement(5.

29、25)*(5.24)The entropy change accompanying any physical or chemical transformation approaches zero as the temperature approaches zero.Hold only for changes involving substances in internal equilibrium. (Simon and others)The Nernst heat theorem(valid for any process)Physical ChemistryChapter 5Determin

30、ation of Conventional Entropies(5.25)*(5.27)H2 (s)O2(s)H2O(s)(5.26)(5.22)*Physical ChemistryChapter 5Determination of Conventional Entropies(3.30)(5.28)*(5.29)For example,0, 1bar, sTfus, 1bar, sTfus, 1bar, lT2, 1bar, lfusHmCP,m(s)CP,m(l)phase changePhysical ChemistryChapter 5Calculation of Hid Hre(5

31、.14)Real gas, PoReal gas, 0 barIdeal gas, 0 bar(b)(a)(c)isothermallyIdeal gas, PochangeisothermallyPhysical ChemistryChapter 5Calculation of Hid Hre(5.14)Real gas, PoReal gas, 0 barIdeal gas, 0 bar(b)(a)(c)isothermallyIdeal gas, Pochangeisothermally(5.15)(5.16)Physical ChemistryChapter 5Calculation

32、of Sid -SreReal gas, PoReal gas, 0 barIdeal gas, 0 bar(b)(a)(c)isothermallyIdeal gas, Pochangeisothermally(5.30)(Prob. 22.92)Physical ChemistryChapter 5Determination of Conventional Entropies(5.29)(5.32)metal at very low Tnonmetal very low T(5.31)(5.33)(5.34)(5.35)For example, let to be (measurable)(5.29)Physical ChemistryChapte