5.1 THERMODYNAMIC ACTIVITY (1) S.J.T.U. Phase Transformation and Applications dG=VdP(dG=-SdT+Vdp,with dT=0) If the gas is ideal (RT/P) then dG=RT=RTd In P P For a real gas,we can define a function,fugacity (f),by analogy to pressure: dG=RTdInf Limf/P=1 P→0 AG=G2-G=RT"dinf=RTI f M-t RT'In SJTU Thermodynamics of Materials Spring2006©X.J.Jin Lecture 9 Chemical equilibrium IlPhase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Spring 2006 © X. J. Jin Lecture 9 Chemical equilibrium II 5.1 THERMODYNAMIC ACTIVITY (1) = ( = − + , dTwithVdPSdTdGVdPdG = )0 If the gas is ideal then : = PRTV )/( PRTd P dP RTGd == ln For a real gas , we can define a function , fugacity (f) ,by analogy to pressure : = ln fRTdGd PLimf = 1/ P → 0 1 2 12 ln ln 2 1 f f RTfdRTGGG ff =−=Δ = ∫ 1 2 12 ln ff μμ =− RT