大连理工大学：《工程热力学》课程教学资源（PPT课件）8 热化学与化学平衡 Thermo-Chemistry & Chemical Equilibrium

8 Thermo-Chemistry& Chemical EquilibriumObjective. Thermo-effect in chemical reaction and evaluation ofreaction heat Theoretical adiabatic combustion temperature. Chemical equilibrium and equilibrium constant Judgment on direction and limitation of chemical reaction Evaluation on equilibrium constant and dissociation

8 Thermo-Chemistry & Chemical Equilibrium Objective • Thermo-effect in chemical reaction and evaluation of reaction heat • Theoretical adiabatic combustion temperature • Chemical equilibrium and equilibrium constant • Judgment on direction and limitation of chemical reaction • Evaluation on equilibrium constant and dissociation

8.1 1st Law Analysis of Chemical Reaction8.1.1 Internal Energy and EnthalpyPotentialUPhysicalphKineticInternalEnergyDependsoncomponentsUChemicalchIrreverent totemperatureUUU=chphH=H+Hchph

8.1 1st Law Analysis of Chemical Reaction 8.1.1 Internal Energy and Enthalpy Internal Energy Physical Chemical Potential Kinetic U ph Depends on components Irreverent to temperature Uch U U U = + ph ch H H H = + ph ch

8.1 1st Law Analysis of Chemical Reaction8.1.2 Work of Chemical ReactionWVolumetricWorkWork-wNon-volumetric WorkExample:ElectricitybyFuelCellWor =W+Wfo1

8.1 1st Law Analysis of Chemical Reaction 8.1.2 Work of Chemical Reaction Work Volumetric Work Non-volumetric Work W We Example: Electricity by Fuel Cell W W W tot e = +

8.1 1st Law Analysis of Chemical Reaction8.1.3 Heat of Chemical ReactionDefinition:The heat transferred between system and surroundingsduring chemical reaction.Q > 0: heat transfer to the systemQ < O: heat transfer from the systemQ = O: adiabatic

8.1 1st Law Analysis of Chemical Reaction 8.1.3 Heat of Chemical Reaction Definition: The heat transferred between system and surroundings during chemical reaction. Q > 0: heat transfer to the system Q < 0: heat transfer from the system Q = 0: adiabatic

8.1 1st Law Analysis of Chemical Reaction8.1.4 1st Law of Chemical ReactionQ=△U+Wot =U,-Ur+W+WSQ=dU +W=dU,-dU,+$W+SW01ProductReact

8.1 1st Law Analysis of Chemical Reaction 8.1.4 1st Law of Chemical Reaction Q U W U U W W =  + = − + + tot P R e δ d δ d d δ δ Q U W U U W W = + = − + + tot P R e Product React

8.2 Thermo-effect of Chemical Reaction8.2.1 Thermo-effect of chemical reactionW.=0T,= TRReaction Heat underandQvConstant Volume: dV =0..W =0,Wor = 0定容热效应等于:.Qv =U,-UR系统内能的变化QpConstantPressure: W = p(Vp -Vr) .:.Wtot = W定压热效应等于系统恰的变化:Qp=Up-Ur+W=Hp-H

8.2 Thermo-effect of Chemical Reaction 8.2.1 Thermo-effect of chemical reaction Constant Volume QV d 0 0, 0 tot V P R V W W Q U U =  = =  = − Constant Pressure QP = −  = ( )  = − + = − P R tot P P R P R W p V V W W Q U U W H H 定容热效应等于 系统内能的变化 定压热效应等于 系统焓的变化 0 Reaction Heat under T T P R = and We =

8.2.1Thermo-effect at Constant Volume and PressureConst. P& TSame reactSame ProductConst.V&TQp = Qv +W = Qv + p(Vp-VR)For Ideal GasQp = Qy +(np -nr)RmTn-gas moles

8.2.1 Thermo-effect at Constant Volume and Pressure Same react Const. P & T Const. V & T Same Product = + = + − ( ) Q Q W Q p V V P V V P R For Ideal Gas ( ) Q Q n n R T P V P R m = + − n－gas moles

8.2.2 Hess LawHess(Russian 1802-1852) Law福The thermo-effect of chemical reaction only dependson the initial and ending state of reaction and is unrelatedwith reaction path.It is important that different reactions can be relatedthrough Hess Law

8.2.2 Hess Law Hess (Russian 1802-1852) Law The thermo-effect of chemical reaction only depends on the initial and ending state of reaction and is unrelated with reaction path. It is important that different reactions can be related through Hess Law

8.2.2 Hess LawExample:C+O,=CO,Op1 = -393520 kJ/kmol(1)CO2(2)CO+=O,=CO,Qp2 = -282990 kJ/kmol2(1)-(2) → Qp3 =Qp1 -Qp2 =-110530 kJ/kmolNOTICE:Hess Law must be applied to the same reaction

8.2.2 Hess Law Example: 2 1 C+ O =CO 2 2 2 1 2 2 2 C+O =CO 393520 kJ/kmol 1 CO+ O =CO 282990 kJ/kmol 2 p p Q Q = − = − (1) (2) (1)－(2) 3 1 2 110530 kJ/kmol Q Q Q p p p = − = − NOTICE: Hess Law must be applied to the same reaction

8.2.3 Temperature Effect00Standard Thermo-effectThe thermo-effect at 101325Pa and 25CaA+bB 台dD+eETwo ways:Qp21. React - Product at T,dD+eEaA+bB2. React T2—T,T,React-Product at TAHRAH,Product T,—T2QplaA+bBdD+eET

8.2.3 Temperature Effect Standard Thermo-effect 0 Qp The thermo-effect at 101325Pa and 25℃. aA bB dD eE +  + aA bB + aA bB + dD eE + dD eE + Qp 2 T2 Qp1 T1 HR HP Two ways: 1. React － Product at T2 2. React T2—T1 React－Product at T1 Product T1—T2