相数组分数自由度数.ppt

6.1 相数，组分数，自由度数相数，组分数，自由度数 6.1.1 概念概念第六章第六章 相平衡相平衡 (1) 相数 P (3) 独立组分数 C(2) 物种数 SC S - R - R′R: 独立化学平衡数 R′: 浓度限制条件 chemical stoichiometric number electroneutrality conditionsCaCO3 (s) = CaO(s)+CO2(g)平衡 0 ＝ ΣBμB ，2NH3(g) ＝ N2 (g) ＋3H2 (g) n H2(g) ＝ 3n N2 (g) x H2(g) ＝ 3x N2 (g) NaCl 水溶液，Na+, Cl-, H+, OH-c(Na+) + c(H+) = c(Cl-) + c(OH-)6.1.2 相律相律 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，6.2.1 H2O的相图的相图 6.2.2 CO2 的相图的相图 t/℃P/MPaOBAC0.518-56.5SolidGasLiquidCO26.3 气液相图气液相图 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 固定, T（沸点）-x相图 6.3.1 p-x相图相图 理想溶液(a) 蒸气组成pA＝yAp pB＝yBpBenzene(A)- toluene(B)system (79.7 ℃)x xB By yB Bp p/ 102kPa/ 102kPa0 00 00.38460.38460.11610.11610.25300.25300.45530.45530.22710.22710.42950.42950.52250.52250.33830.33830.56670.56670.52250.52250.45320.45320.66560.66560.664990.664990.54510.54510.75740.75740.71660.71660.63440.63440.81790.81790.77220.77220.73270.73270.87820.87820.83310.83310.82430.82430.92400.92400.89070.89070.91890.91890.96720.96720.91790.91790.95650.95650.98270.98270.98450.98451.0001.0001.0001.0000.99820.9982(b) 相图说明(c) 杠杆规则 The lever rule is so called because a similar rule relates the masses at two ends of a lever to their distances from a pivot. nl = n l6.4 T-x相图相图 Benzene(A)- toluene(B)system (p=101.325Pa)t t/°C/°Cx xB By yB B110.62110.620 00 0108.75108.750.0420.0420.0890.089104.87104.870.1320.1320.2570.257103.00103.000.1830.1830.3840.384101.52101.520.2190.2190.3950.39597.7697.760.3250.3250.5300.53095.0195.010.4670.4670.6190.61992.7992.790.4830.4830.6880.68890.7690.760.5510.5510.7420.74288.6388.630.6280.6280.8000.80086.4186.410.7120.7120.8530.85384.1084.100.8100.8100.9110.91181.9981.990.9000.9000.9580.95880.1080.101.0001.0001.0001.000 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 The number of theoretical plates is the number of steps needed to bring about a specified degree of separation of two components in a mixture. The two systems shown correspond to (a) 3, (b) 5 theoretical plates. (b) Azeotropes A high-boiling azeotrope. When the liquid of composition a is distilled, the composition of the remaining liquid changes towards b but no further.  A low-boiling azeotrope. When the mixture at a is fractionally distilled, the vapour in equilibrium in the fractionating column moves towards b and then remains unchanged.The temperature-composition diagram of H2O(A) - C2H5OH(B)0.00.20.40.60.81.0H2O(A)C2H5OH(B)xByBt/℃12010060800.00.20.40.60.81.0p=101325PaxB=0.897yB=0.89778.15℃ The isopleth through e corresponds to the eutectic composition, the mixture with lowest melting point. 6.6 液固相图液固相图6.6.1 Eutectics 热分析法，步冷曲线CED: s(A)+ s(B)+lE(A+B)t*A Et*B E液相线t*A Ct*B D固相线E: 共熔点(b)反应体系Øcongruent meltingØincongruent melting6.6.2 Ultrapurity and controlled impurityØZone refiningØPartially miscibleCED — s(A+B)+ s(A+B)+lE(A+B)。