相数组分数自由度数

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1、6.1相数，组分数，自由度数6.1.1概念第六章相平衡(1)相数P(3)独立组分数C(2)物种数SCS-R-R′R:独立化学平衡数R′:浓度限制条件chemicalstoichiometricnumberelectroneutralityconditionsCaCO3(s)=CaO(s)+CO2(g)平衡0＝ΣBμB，2NH3(g)＝N2(g)＋3H2(g)nH2(g)＝3nN2(g)xH2(g)＝3xN2(g)NaCl水溶液，Na+,Cl-,H+,OH-c(Na+)+c(H+)=c(Cl-)+c(OH

2、-)6.1.2相律f=C-P+2(4)自由度数f为确定系统的状态，我们定义平衡系统的独立可变的变量的数目6.2单组分相图f＝C－P＋2=1－P＋2＝3－Pf≥0，P≥1，3≥P≥1P＝1，f＝2，P＝2，f＝1，P＝3，f＝0，6.2.1H2O的相图6.2.2CO2的相图t/℃P/MPaOBAC0.518-56.5SolidGasLiquidCO26.3气液相图f＝C－P＋2=2－P＋2＝4－Pf≥0，P≥1，4≥P≥1P＝1，f＝3，P＝2，f＝2，P＝3，f＝1，P＝4，f＝0，T固定，p-x相图p固

3、定,T（沸点）-x相图6.3.1p-x相图理想溶液(a)蒸气组成pA＝yAppB＝yBpBenzene(A)-toluene(B)system(79.7℃)xByBp/102kPa000.38460.11610.25300.45530.22710.42950.52250.33830.56670.52250.45320.66560.664990.54510.75740.71660.63440.81790.77220.73270.87820.83310.82430.92400.89070.91890.9672

4、0.91790.95650.98270.98451.0001.0000.9982(b)相图说明(c)杠杆规则Theleverruleissocalledbecauseasimilarrulerelatesthemassesattwoendsofalevertotheirdistancesfromapivot.nl=nl6.4T-x相图Benzene(A)-toluene(B)system(p=101.325Pa)t/°CxByB110.6200108.750.0420.089104.870.132

5、0.257103.000.1830.384101.520.2190.39597.760.3250.53095.010.4670.61992.790.4830.68890.760.5510.74288.630.6280.80086.410.7120.85384.100.8100.91181.990.9000.95880.101.0001.000理想溶液的T-x相图是以A的挥发度较大(a)混合物的分馏Thenumberoftheoreticalplatesisthenumberofstepsneededtob

6、ringaboutaspecifieddegreeofseparationoftwocomponentsinamixture.Thetwosystemsshowncorrespondto(a)3,(b)5theoreticalplates.(b)AzeotropesAhigh-boilingazeotrope.Whentheliquidofcompositionaisdistilled,thecompositionoftheremainingliquidchangestowardsbbutnofurthe

7、r.Alow-boilingazeotrope.Whenthemixtureataisfractionallydistilled,thevapourinequilibriuminthefractionatingcolumnmovestowardsbandthenremainsunchanged.Thetemperature-compositiondiagramofH2O(A)-C2H5OH(B)0.00.20.40.60.81.0H2O(A)C2H5OH(B)xByBt/℃12010060800.00.2

8、0.40.60.81.0p=101325PaxB=0.897yB=0.89778.15℃Theisopleththroughecorrespondstotheeutecticcomposition,themixturewithlowestmeltingpoint.6.6液固相图6.6.1Eutectics热分析法，步冷曲线CED:s(A)+s(B)+lE(A+B)t*AEt*BE液相线t*ACt*BD固相线E:共熔点(b)反应