(11.5.1)--6.5RealGasIsotherm.pdf

Real Gas IsothermReal Gas Isotherm Real Gas Isotherm1 Andrews Experiment2 The Tephigram of Real Gas31.Measurement of real gas isotherm Changing the volume of the gas(that is changing the pressure)with constant T0 will cause:pVabcdabGasbcThe Gas-liquid CoexistencecdLiquidTwo phases coexist with constant pressure and saturated vapor pressurepnkTFirst-order phase transition:sharp change of the molar entropy and molar volume,the existence of latent heat,and the possible occurrence of the supercooled or superheated phase transition.2.Andrews Experiment The English physicist Andrew initially studied the real gas isotherms(1869)in a systematic manner,Each point on the left dotted line,which is regarded as the liquid evaporation curve,indicates the state of liquid under the condition of gas-liquid coexistence at different temperatures;The three areas:Gas(g)、Liquid(l)、Gas-liquid Coexistence(g-l)Each point on the right dotted line,which is defined as the vapor condensation curve,indicates the state of saturated vapor at different temperatures;pV The peak of the dotted line symbolizes the critical point.Carbon dioxide304KcT Continuous phase transition:without the absorption and discharge of latent heat,failing coexistence of two phases,and no occurrence of supercooling and overheating(second-order phase transition).3.T-S Figure of Real Gas The entropy Sg and Sl of point B and C respectively represent the entropy of the gas phase and the liquid phase,indicating Sg Sl as illustrated in the figure Liquid remains orderly within short distance,while gas is disordered even within short distance,which reveals that considering the certain temperature and pressure,the molar entropy Sg exceeds Sl.As for the reversible process,T dS meets dQ,which means that the area of range under the line BC can be calculated as follows:T(Sg Sl)=T(Sg,mSl,m)=LV,m What the heat of vaporization refers to is the heat absorbed during the liquid-gas phase transition with the same temperature and pressure,while what LV,m means is the molar heat of vaporization.TThanks！