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1、Ideal Gases/Perfect Gases,Gases: A gas is a fluid which has no intrinsic shape, and which expands indefinitely to fill any container in which it is held.,Ideal Gases: The amount of substance of which it is comprised, n (mole) The temperature of the gas, T (Kelvin) The pressure of the gas, P (Pascal)
2、 The volume occupied by the gas, V (m3),Thermodynamics,Ideal Gases/Perfect Gases,Gas Laws: Boyles law: PV=constant at constant T and n Charles law: VT at constant P and n Avogadros Principle: Vn at constant P and T,Chapter 1,The four parameters are not independent.,The relations among them are expre
3、ssed in the gas laws.,Ideal Gas Law/Perfect Gas Equation: PV = nRT R is gas constant (1.18)*,Chapter 8,Real Gases,Compression Factors,Real gases do not obey the perfect gas equation exactly. The measure of the deviation from ideality of the behavior of a real gas is expressed as the compression fact
4、or Z:,(8.1),Real Gases,Physical Chemistry,Real Gas Equations of State,(8.2),van der Waals equation,Ideal Gas Law/Perfect Gas Equation: PV = nRT (1.18)*,Real Gases,Physical Chemistry,范德华（Van der Waals）方程,式中 是压力校正项，即称为内压力； 是体积校正项，是气体分子占有的体积。,Real Gases,Physical Chemistry,实际气体的状态方程,: to correct the eff
5、ect of intermolecular attractive forces on the gas pressure,b: the volume excluded by intermolecular repulsive forces,Virial Equation of State,(8.4),Redlich-Kwong Equation,(8.3),Real Gases,Physical Chemistry,Real Gas Equations of State,The limited accuracy of the data allows evaluation of only B(T)
6、and sometimes C(T).,Virial Equation of State,(8.5),(8.6),(8.7),low P,vdW gas,(8.2),Real Gases,Physical Chemistry,(8.4),Power series in 1/Vm,Power series in P,Gas Mixtures,(8.10),For a mixture of two gases, 1 and 2, use a two-parameter equation,Real Gases,Physical Chemistry,x1 and x2: the mole fracti
7、ons of the components,b: a weighted average of b1 and b2,a: related to intermolecular attractions,(a1a2)1/2: intermolecular interaction between gases 1 and 2,Isotherms of H2O,P,Vm,400 oC,U,R,J,N,Y,374 oC,300 oC,200 oC,H2O,L + V,L,V,L,G,H,T,S,K,M,W,Condensation,T 374 oC,gas condenses to liquid when P
8、,T = 300 oC,R(vapor)S(saturated vapor), P, V,S(saturated vapor)W(saturated liquid), P, V ,W(saturated liquid)Y(liquid), P , V,Real Gases,Physical Chemistry,t/,A,D,C,0.00611,0.01,solid,gas,liquid,O,P / 10 5 Pa,374.2,218 atm,H2O phase diagram: P T,99.974,1 atm,0.0024,I,R,S,Y,Tf,Tb,T3,Real Gases,Physic
9、al Chemistry,400 oC,Condensation,T 374 oC,No amount of compression will cause the separation out of a liquid phase in equil. with the gas.,T = 374 oC,Critical temperature Tc,Critical pressure Pc,Critical volume Vm,c,Critical constants,Real Gases,Physical Chemistry,Fig. 8.3,Critical constants,Critica
10、l T (Tc), Tc(CO2)=304.2 K,Critical P (Pc), Pc(CO2)=7.38 MPa,Critical molar V (Vm,c), Vm,c(CO2)=9410-6 m3mol-1,Real Gases,Physical Chemistry,Table 8.1 Critical Constants,Real Gases,Physical Chemistry,Fluid,There is a continuity between the gaseous and the liquid states. In recognition of this continu
11、ity, the term fluid is used to mean either a liquid or a gas.,An ordinary liquid can be viewed as a very dense gas. Only when both phases are present in the system is there a clear-cut distinction between liquid and gaseous states.,For a single-phase liquid system it is customary to define as a liqu
12、id a fluid whose temperature is below Tc and whose molar volume is less than Vm,c.,If these two conditions are not met, the liquid is called a gas. So a further distinction between gas and vapor can be made, but these two words are used interchangeably in this book.,Real Gases,Physical Chemistry,Sup
13、ercritical fluid,A supercritical fluid is one whose T and P satisfy,A supercritical fiquid usually has liquidlike density but its viscosity is much lower than typical for a liquid and diffusion coefficients in it are much higher than in liquids.,T Tc and P Pc,Real Gases,Physical Chemistry,Supercriti
14、cal fluid,Supercritical CO2 is used commercially as a solvent to decaffeinate coffee.,Real Gases,Physical Chemistry,CO2,在Tc以上，无论加多大压力均不会使气体液化。所以Tc是在加压下使气体液化的最高温度。在Tc以下，对气体加压力均可使气体液化。,Tc以上，压力接近或超过的流体叫超临界流体。,Real Gases,Physical Chemistry,超临界流体,Critical data and equations of state,Differentiating the v
15、an der Waals equation (8.2),and,At the critical point:,(8.12),Application of the conditions (8.12) gives,and,(8.13),Real Gases,Physical Chemistry,Critical data and equations of state,Division of the first equation in (8.13) by the second yields,From van der Waals equation:,(8.14),Use of (8.15) in th
16、e first equation in (8.13) gives,and,(8.16),(8.15),Real Gases,Physical Chemistry,Critical data and equations of state,Substitution of (8.15) and (8.16) into (8.14),(8.14),gives,(8.16),(8.15),(8.17),Real Gases,Physical Chemistry,Critical data and equations of state,Substitution of (8.15) and (8.16) i
17、nto (8.14),Three equations for two parameters, a and b,(8.16),(8.15),(8.17),(8.18),vdW gas,Real Gases,Physical Chemistry,Critical data and equations of state,Combination of (8.15) to (8.17),(8.16),(8.15),(8.17),(8.19),Real Gases,Physical Chemistry,Predicts the compressibility factor at the critical
18、point,Van der waals equation,Critical data and equations of state,(8.19),ideal gas,(8.20),(8.21),(8.22),R-K equation,Real Gases,Physical Chemistry,Van der waals equation,Selected equations of state,Real Gases,Physical Chemistry,Selected equations of state,Real Gases,Physical Chemistry,The law of cor
19、responding states,The critical constants are characteristic properties of gases,The reduced variables of a gas by dividing the actual variable by the corresponding constant.,The observation that the real gases at the same reduced volume and reduced temperature exert the same reduced pressure is called the law (principle) of corresponding states.,(8.27),reduced pressure,reduced volume,reduced temperature,(8.28),Real Gases,Physical Chemistry,