Chapter 8 Real Gases (1).ppt

Chapter 8 Real Gases (1).ppt.pptIdeal 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: 1. The amount of substance of which it is comprised, n (mole) 2. The temperature of the gas, T (Kelvin) 3. The pressure of the gas, P (Pascal) 4. The volume occupied by the gas, V (m 3) Thermodynamics Ideal Gases/Perfect Gases Gas Laws: 1. Boyle ’ s law : PV =constant at constant T and n 2. Charles ’ law : V?T at constant P and n 3. Avogadro ’ s Principle : V?n at constant P and T Chapter 1 The four parameters are not independent. The relations among them are expressed in the gas laws. Ideal Gas Law/Perfect Gas Equation: PV = nRT R is gas constant () * Chapter 8 Real pression 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 factor Z: RT PV TPZ m?),( () Real Gases ZP 200 K 500 K 1000 K 200 K 1000 K 0 300 600 900 3210 CH 4 ZP H 20 100 200 300 0 0 oCN 2 CH 4 Physical Chemistry Real Gas Equations of State ?? RT bVV aP mm??????????? 22m mV abV RT P???() van der Waals equation Ideal Gas Law/Perfect Gas Equation: PV = nRT () * RT PV m? 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。 b 2m/ a V RT bVV aP mm???) )(( 2 RT PV m? Real Gases Physical Chemistry 实际气体的状态方程: to correct the effect of intermolecular attractive forces on the gas pressure 2m/ a V b : the volume excluded by intermolecular repulsive forces Virial Equation of State ???????????? 32)()()(1 m m m mV TDV TCV TB RT PV () Redlich-Kwong Equation 2/1)(TbVV abV RT P mm m????() Real Gases Physical Chemistry Real Gas Equations of State The limited accuracy of the data allows evaluation of only B(T) and sometimes C(T). Virial Equation of State ])(')(')('1[ 32??????PTDPTCPTB RT P