物理化學英文課件：chapter12-1 Multicomponent Phase Equilibrium

1、Chapter 12Multicomponent Phase EquilibriumPhysical ChemistryMulticomponent Phase1Question and Answering Physical ChemistryA Students Question我昨天晚上看了第9章的38題，想到了一個問題，在2種組分的理想混合溶液中，一種組分所占整個體系的摩爾分數(shù)與它的蒸汽所占整個體系氣體的摩爾分數(shù)和它的液態(tài)部分所占整個體系液態(tài)部分的摩爾分數(shù)之間有什么關系？也就是 與 和 三者有什么關系？是不是 ？但仔細想又不對！ Question:2Question and Answer

2、ing Physical ChemistryA Students QuestionRaoults Law:Answers.Daltons Law:ABCase (1)Case (2)Case (3)3Colligative Properties Colligative properties stem from the reduction of the chemical potential of the liquid solvent as a result of the presence of solute.Colligative PropertiesVapor-pressure lowerin

3、gFreezing-point depressionBoiling-point elevationOsmotic pressureThe solute is not volatileThe solute does not dissolve in the solid solventPhysical ChemistryMulticomponent Phase4Colligative Properties Vapor-pressure loweringPA/torrx (sucrose)0-400.1Fig. 12.1nonvolatile solute (12.1)nonvolatile solu

4、te (12.2)(No contribution to the vapor)If the solution is very dilute, ideally dilute solution, nonvolatile solute (12.3)ideally dilute solutionPhysical ChemistryMulticomponent Phase5Colligative Properties Freezing-point depression(12.13)ideally dil. soln., pure A freezes outmolar freezing-point-dep

5、ression constantATFig. 12.2A(s)A(l)A(sln)Freezing-point depression(12.15)*(12.16)Physical ChemistryMulticomponent Phase6Colligative Properties Boiling-point elevationideally dil. soln., nonvol. solutemolar boiling-point-elevation constant(12.18)*(12.19)ATA(l)A(s)A(v)Boiling-point elevationPhysical C

6、hemistryMulticomponent Phase7Colligative Properties The vapor pressure of a pure liquid represents a balance between the increased disorder arising from vaporization and the decreased disorder of the surroundings. When solute is present, the disorder of the condensed phase is relatively higher than

7、that of the pure liquid, and there is a decreased tendency to acquire the disorder characteristic of the vapor.Physical ChemistryMulticomponent Phase8Colligative Properties Equilib. at T for vapor and liquid phases of the solventrearranges to(Assuming T independent)When xB=0, the boiling point is an

8、dPhysical ChemistryMulticomponent Phase9Colligative Properties Suppose that the amount of solute present is so small that thenPhysical ChemistryMulticomponent Phase10Colligative Properties sinceit also follows that(P344)For very dilute solutionPhysical ChemistryMulticomponent Phase11Colligative Prop

9、erties Osmotic pressure(12.20)(12.26)Equal at equilibriumPure ASolution of B+ASemipermeable membrane (A)ideally dil. soln.(12.27)*vant Hoffs law, valid in the limit of infinite dilutionPhysical ChemistryMulticomponent Phase12Colligative Properties Osmotic pressureThe osmotic pressure in a nonideally

10、 dilute nonelectrolyte two-component solution(12.28)(8.4)In the limit of infinite solutionvant Hoff lawPhysical ChemistryMulticomponent Phase13f = 224，1，f32，f23，f14，f0 Two-component phase diagrams If one phase, then three freedoms:TPxInstead of plotting complete phase diagrams (three dimensional), u

11、sually consider only portion of the phase diagram at a time.Physical ChemistryMulticomponent Phase14Two-component phase diagrams Keep one constant, get relations for two variablesKeep T constant, get P-x (very commonly used)Keep P constant, get T-x (commonly used)Keep x constant, get T-P (not very c

12、ommonly used)Physical ChemistryMulticomponent Phase15l(A+B)C6H5CH3(A)C6H6 (B)yB0.00.20.40.60.81.00.80.60.20.40.00.00.20.40.60.81.0v(A+B)T=79.7 yG,B=0.60HF xBl(A+B)Il(A+B)v(A+B)P / 102 kPatie lineADEisopleth lineH,I endpointIdeal solution at fixed TPhysical ChemistryMulticomponent Phase16l(A+B)010.80

13、.60.20.40.00.00.20.40.60.81.0v(A+B)T=79.7 HF xBl(A+B)Il(A+B)v(A+B)P / 102 kPaADETwo-component phase diagrams (12.40)(12.39)Lever rulePhysical ChemistryMulticomponent Phase170.01.0l(A+B)C6H5CH3(A)C6H6 (B)xByB12010060800.00.00.20.40.60.81.0t/v(A+B)P=101 325PaliquidSQRLNTemperature vs composition liqui

14、d-vapor phase diagram (C6H5CH3(A) - C6H6 (B) )l+vIdeal solution at fixed PvaporBoiling-point curvePSuccessive boilings and condensations of a liquid originally of composition a1 lead to a condensate that is pure Ba1Fractional distillationPhysical ChemistryMulticomponent Phase18Two-component phase di

15、agrams Nonideal SolutionA low-boiling azeotropeA high-boiling azeotropeminimum-boiling azeotropemaximum-boiling azeotropelVapor l + vVapor Liquid l + vl + vl + vAzeotropes Physical ChemistryMulticomponent Phase19Two-component phase diagrams A maximum in the phase diagram may occur when the favorable

16、 interactions between A and B molecules reduce the vapor pressure of the mixture below the ideal value Phase diagram showing a minimumPhase diagram showing a maximumThe mixture: form an azeotropeWhen the azeotropic composition has been reached, distillation cannot separate the two liquids because th

17、e condensate has the same composition as the azeotropic liquid.Physical ChemistryMulticomponent Phase20Two-component phase diagrams Examples of azeotrope formation:Hydrochloric acid/water at 80% by mass of water and boils unchanged at 108.6 oC.Ethanol/water at 4% by mass of water and boils unchanged

18、 at 78.0 oC.A high-boiling azeotrope.A low-boiling azeotrope.Physical ChemistryMulticomponent Phase21Two-component phase diagrams Liquid-liquid equilibriumTwo partially miscible liquids0.00.20.40.60.81.0l(A+B)H2O(A)C6H5NH2(B)xBt/1601204080P=const.TCH2O (A) -C6H5NH2(B)Two phasesone phaseTC: critical solution TBelow TC, two-phase region (miscibility gaps)Above TC, the liquids are completely miscible, one phase regionPhysical ChemistryMulticomponent Phase22Two-component phase diagrams W(C6H15N)water-triethylamineTwo phasesOne phaseFig. 12.17 (a)Physical ChemistryMulticompon