物理化學(xué)英文課件：chapter02 The First Law of Thermodynamics

1、1Key NotesIdeal Gases/Perfect GasesSummaryPhysical ChemistryGases: a fluid which has no intrinsic shape, and which expands indefinitely to fill any container in which it is held.The ideal gas equations: the relations among the amount of gas substance, temperature, pressure and volume. PV = nRTPVm =

2、RTVm: molar gas volume2Key NotesIdeal Gases/Perfect GasesSummaryPhysical ChemistryDaltons law: the total pressure exerted by a mixture of ideal gases in a volume is equal to the arithmetric sum of the partial pressures.Ptotal = ntotalRT/VPartial pressure: the pressure exerted by each component in a

3、gaseous mixture.Px = nxRT/VPi = xiPtotalnx: molexi: mole fraction3Isothermal: A system which is held at constant temperatureAdiabatic: A system in which energy may be transferred as work, but not as heat.CHAPTER 2 The First Law of Thermodynamics Basic ConceptsDiathermic: A system which allows energy

4、 to escape as heat through its boundary if there is a difference in temperature between the system and its surroundings.Physical ChemistryChapter 24Internal energy: Total amount of energy in a system. The sum total of all kinetic and potential energy within the system. Internal energy changes: The s

5、ign of UNegative values: a system loses energy to the surroundingsPositive values: a system gains energy from the surroundings Physical ChemistryChapter 2Internal Energy5Extensive property： The value of the property changes according to the amount of material which is present (e.g., mass, volume, in

6、ternal energy)Intensive property：independent of the amount of material which is present (e.g., temperature, density)Thermodynamic Properties of systemState functions: the value of a particular property for a system depends solely on the state of the system at time (e.g., pressure, volume, internal e

7、nergy, entropy)Path functions: A property depends upon the path by which a system in one state is changed into another state (e.g., work, heat)Physical ChemistryChapter 26Work: the transfer of energy as orderly motiondue to energy being expanded against an opposing force (in mechanical terms)Physica

8、l ChemistryChapter 2Workdw Fx dx(2.10)*Reversible P-V Work(2.31)closed system, reversible process(2.30)*dwrev = -PdVclosed system, reversible process7Reversible P-V Work(a) Expansion (dV 0)(b) Compression (dV T1)Tf(2.34)Specific heat capacityHeatPhysical ChemistryChapter 2T1TfT211(2.35)Heatclosed sy

9、st., P const.(2.36)(2.37)(2.38)(2.34)Physical ChemistryChapter 212The total energy of an isolated thermodynamic system is constantthe conservation of energyThe First Law of Thermodynamics Energy cannot be created or destroyedClosed system at rest in the absence of external fieldsU = q + w(2.41)*q is

10、 the heat supplied to the systemw is the work done on the systemU is the internal energy of the systemPhysical ChemistryChapter 213Heat and Work(2.44)*The calorie defined by (2.44) is called thermodynamical calorie, calthBoth are measures of energy transfer, and both have the same units as energy.Th

11、e unit of heat can be defined in terms of joule.Physical ChemistryChapter 214Enthalpy(2.45)*Let qP be the heat adsorbed in a constant-pressure process in a closed system, from the first lawat cons P,closed syst. P-V work only(2.46)Since U, P, V are state functions, H is a state function.P1=P2=PPhysi

12、cal ChemistryChapter 215For any change of state, the enthalpy change HU and V are extensive, H is extensive.(2.45)*(2.47)at constant P(2.48)The molar enthalpy of a pure substance EnthalpyPhysical ChemistryChapter 216(closed syst., P-V work only, V const.)Let qV be the heat adsorbed in a constant-vol

13、ume process in a closed system, if it can do only P-V work, thendw = - PdV = 0Since dV = 0Then dw = 0So w = 0From the first law(2.49)EnthalpyPhysical ChemistryChapter 217For a reaction involving a perfect gas(1 mole of gaseous CO2 is created)Exampleat 298 K at constant P(2.48)EnthalpyPhysical Chemis

14、tryChapter 218Exothermic and EndothermicHeat change in systemProcessValue of HHeat loss(heat lost to the surroundings)Heat gain(heat gained from the surroundings)ExothermicEndothermicNegative (H 0)The sign of enthalpy change indicates the direction of heat flowPhysical ChemistryChapter 219Heat Capac

15、itiesheat capacity at constant volume CV (isochoric heat capacity)heat capacity at constant pressure CP (isobaric heat capacity)(2.50)*(2.52)*(2.51)*Physical ChemistryChapter 220Heat Capacities CP and CV give the rates of change of H and U with temperature T.(2.53)*(2.50)*(2.52)*(2.51)*Physical Chem

16、istryChapter 221Heat CapacitiesThe slope of the curve at any temperature ABUTconstant volume heat capacity (isochoric heat capacity) CV(2.49)Physical ChemistryChapter 222Heat CapacitiesThe slope of the H-T curve at any temperature ABHTconstant pressure heat capacity (isobaric heat capacity) Cp(2.46)

17、Physical ChemistryChapter 223(2.57)The relation between CP and CVPhysical ChemistryChapter 224At constant PSubstitution of (2.59) into (2.57)(2.60)(2.58)(2.59)(2.57)Physical ChemistryChapter 225(2.60)(2.61)Why?(first law)Physical ChemistryChapter 226(2.61)(1) In a constant pressure process, part of

18、the added heat goes into the work of expansion (2) (2.60)internal pressureintermolecular potential energyPhysical ChemistryChapter 227Homework (2.1-2.6)Physical Chemistry2.62.122.262.29Chapter 2Due next Monday before the class28Joule experimentChamber A: filled with a gasChamber B: is evacuatedValve

19、: is closedValve: is openedChamber A: releases a gasChamber B: filled with a gasAfter equilibrium is reachedThe temperature change in the system is measured by the thermometer. ABAdiabatic wallFig. 2.6valvethermometerPhysical ChemistryChapter 229Joule experimentq = 0 (the system is surrounded by adi

20、abatic walls)ABAdiabatic wallFig. 2.6valvethermometerw = 0 (gas expansion into a vacuum)U = q + w = 0 + 0 = 0 (a constant-energy process)The experiment measures T with V at constant internal energy, (2.62)Joule coefficientPhysical ChemistryChapter 230Joule experimenttotal differential of z(x,y) (2.6

21、2)When y is kept constant(1.30)*total differential of z(r,s,t)When x is kept constant(1.31)Physical ChemistryChapter 231Joule experimentDivision by dzy gives (2.62)When z stays constantFrom the definition of the partial derivative(1.32)*(1.33)(1.30)*Physical ChemistryChapter 232Joule experimentDivis

22、ion by dyz gives (2.62)Using (1.32) with x and y interchanged and multiplied by(1.34)*Physical ChemistryChapter 233Joule experimentReplaced x, y, z with T, U, and V, gives (2.62)When (1.32), (2.53) and (2.62) were used (2.63)Physical ChemistryChapter 234Joule-Thomson experimentP1P1, V1, T1Porous Plu

23、gP2(a)(b)(c)P1P2P2, V2, T2P1P1P2P2Adiabatic WallFig. 2.7 The Joule-Thomson experiment.P2 P1BPhysical ChemistryChapter 235The slow throttling of a gas through a rigid, porous plug. The system is enclosed in adiabatic walls. The left piston is held at a fixed pressure P1, the right piston is held at a

24、 fixed pressure P2 (P1).The partition B is porous but not greatly so. This allows the gas to be slowly forced from one chamber to the other. Because the throttling process is slow, pressure equilibrium is maintained in each chamber. Essentially all the pressure drop from P1 to P2 occurs in the porou

25、s plug.P1P1, V1, T1P2(a)(b)P1P2P2, V2, T2P1P1P2P2P2 P1B(c)Physical ChemistryChapter 236The work done on the gas in throttling it through the plug w P1V1 P2 V2q 0 (adiabatic process)U2 - U1 q + w w P1V1 P2 V2 U2P2 V2U1P1V1 H2H1orH 0 (2.64)*Joule-Thomson coefficientJoule-Thomson experimentPhysical Che

26、mistryChapter 237Calculate the work done when 50 g of iron reacts with hydrochloric acid in (a) a closed vessel of fixed volume (b) an open beaker at 25 oC.Example:In (a) the volume cannot change, so no work is doneIn (b) the gas gives back the atmosphere and thereforeThe amount of H2 producedPhysic

27、al ChemistryChapter 238Calculate the work done when 50 g of iron reacts with hydrochloric acid in (a) a closed vessel of fixed volume (b) an open beaker at 25 oC.Example:The reaction is1 mole H2 is generated when 1 mole Fe is consumed Molar mass of FeThe system does 2.2 kJ of work driving back the a

28、tmospherePhysical ChemistryChapter 239Reversible isothermal process in a perfect gas(2.74)(2.75)Reversible adiabatic process in a perfect gasA perfect gasPhysical ChemistryChapter 240Reversible adiabatic process, CV is constant(2.75)If CV,m is constant (independent of T over a wide temperature range

29、)A perfect gas(2.76)Physical ChemistryChapter 241An alternative equation can be obtained by usingA perfect gas(2.76)Physical ChemistryChapter 242A perfect gas(2.76)CP,m - CV,m = R (2.72)*Heat capacity ratio(2.77)(2.78)Physical ChemistryChapter 243Thermodynamic Processes Key NotesCyclic process: the

30、systems final state is the same as the initial state.initialfinal cyclicPhysical ChemistryChapter 2Reversible process: the system is always infinitesimally close to equilibrium, and an infinitesimal change in conditions can restore both system and surroundings to their initial state.Isothermal proce

31、ss: temperature is held constant throughout the process.Adiabatic process: dq=0 and q=0Isochoric (isobaric) process: volume (pressure) is held constant throughout the process.44Reversible phase change at constant T and P: Constant-pressure heating with no phase change: Constant-volume heating with n

32、o phase change:Perfect-gas change of state:Reversible isothermal process in a perfect gas Reversible adiabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Reversible phase change at constant T and P:Calculation of First-Law QuantitiesPhysical ChemistryChapter 245Reversi

33、ble phase change at constant T and P:Calculation of First-Law QuantitiesPhysical ChemistryChapter 246Reversible phase change at constant T and P: Constant-pressure heating with no phase change: Constant-volume heating with no phase change:Perfect-gas change of state:Reversible isothermal process in

34、a perfect gas Reversible adiabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Calculation of First-Law QuantitiesPhysical ChemistryChapter 247Reversible phase change at constant

35、T and P:Constant-pressure heating with no phase change:Calculation of First-Law Quantities(2.79)Physical ChemistryChapter 248Reversible phase change at constant T and P: Constant-pressure heating with no phase change: Constant-volume heating with no phase change:Perfect-gas change of state:Reversibl

36、e isothermal process in a perfect gas Reversible adiabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no phase change:Calculation of First-Law Quanti

37、tiesPhysical ChemistryChapter 249Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no phase change:Calculation of First-Law Quantities(2.80)Physical ChemistryChapter 250Reversible phase change at constant T and P: Constant-pressur

38、e heating with no phase change: Constant-volume heating with no phase change:Perfect-gas change of state:Reversible isothermal process in a perfect gas Reversible adiabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Reversible phase change at constant T and P:Constant-

39、pressure heating with no phase change:Constant-volume heating with no phase change:Perfect-gas change of state:Calculation of First-Law QuantitiesPhysical ChemistryChapter 251Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no ph

40、ase change:Perfect-gas change of state:Calculation of First-Law Quantities(2.81)Physical ChemistryChapter 252Reversible phase change at constant T and P: Constant-pressure heating with no phase change: Constant-volume heating with no phase change:Perfect-gas change of state:Reversible isothermal pro

41、cess in a perfect gas Reversible adiabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no phase change:Perfect-gas change of state: Reversible isother

42、mal process in a perfect gas Calculation of First-Law QuantitiesPhysical ChemistryChapter 253Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no phase change:Perfect-gas change of state: Reversible isothermal process in a perfect

43、 gas Calculation of First-Law Quantities(2.74)Physical ChemistryChapter 254Reversible phase change at constant T and P: Constant-pressure heating with no phase change: Constant-volume heating with no phase change:Perfect-gas change of state:Reversible isothermal process in a perfect gas Reversible a

44、diabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no phase change:Perfect-gas change of state: Reversible isothermal process in a perfect gasRevers

45、ible adiabatic process in a perfect gas:Calculation of First-Law QuantitiesPhysical ChemistryChapter 255Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no phase change:Perfect-gas change of state: Reversible isothermal process i

46、n a perfect gasReversible adiabatic process in a perfect gas:Calculation of First-Law Quantities(2.81)Physical ChemistryChapter 256Reversible phase change at constant T and P: Constant-pressure heating with no phase change: Constant-volume heating with no phase change:Perfect-gas change of state:Rev

47、ersible isothermal process in a perfect gas Reversible adiabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no phase change:Perfect-gas change of sta

48、te: Reversible isothermal process in a perfect gasReversible adiabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Calculation of First-Law QuantitiesPhysical ChemistryChapter 257Reversible phase change at constant T and P:Constant-pressure heating with no phase change:Constant-volume heating with no phase change:Perfect-gas change of state: Reversible isothermal process in a perfect gasReversible adiabatic process in a perfect gas:Adiabatic expansion of a perfect gas into vacuum.Calculation of First-Law QuantitiesPhysical ChemistryChapter 258Molecular interpret