2.1 Entropy as a State Function(1) S.J.T.0. Phase Transformation and Applications For a close system the reversible heat flow divided by the absolute temperature of the system is a state or point function. T 可逆过程的热温商！ Entropy S The unit of entropy:joules per kelvin in SI system. Relationship between entropy changes and transfers of heat and irrevisibilities in a macroscopic sense. SJTU Thermodynamics of Materials Fall 2012 ©X.J.Jin Lecture 3 Second law I
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Fall 2012 © X. J. Jin Lecture 3 Second law I 2.1 Entropy as a State Function(1) For a close system the reversible heat flow divided by the absolute temperature of the system is a state or point function. Entropy S The unit of entropy: joules per kelvin in SI system. Relationship between entropy changes and transfers of heat and irrevisibilities in a macroscopic sense. dS T Qrev = δ 可逆过程的热温商！
2.1 Entropy as a State Function(2) S.J.T.0. Phase Transformation and Applications First Law: dU=80+oW du=0o+Wron =80+8W For a reversible path: du=sre+oWrer 0re=80-Wey +oW Lost work -olw The difference between the work that could have been done had the process been reversible and the actual work that was done A measure of the irreversibilities involved in the transfers of energy between the system and surroundings. 0rer=80-8tw 8lw=8W,-8W SJTU Thermodynamics of Materials Fall 2012 ©X.J.Jin Lecture 3 Second law I
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Fall 2012 © X. J. Jin Lecture 3 Second law I 2.1 Entropy as a State Function(2) First Law: dU = δQ +δW dU = δQrev +δWrev For a reversible path: dU = δQrev +δWrev = δQ +δW δQrev = δQ −δWrev +δW Lost work −δlw The difference between the work that could have been done had the process been reversible and the actual work that was done. A measure of the irreversibilities involved in the transfers of energy between the system and surroundings. δQrev = δQ −δlw δlw = δWrev − δW
2.1 Entropy as a State Function(3) S.J.T.0. Phase Transformation and Applications A,reversible B,irreversible P w-fow P Lost work Reversible work Actual work V V Volume Volume SJTU Thermodynamics of Materials Fall 2012 ©X.J.Jin Lecture 3 Second law I
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Fall 2012 © X. J. Jin Lecture 3 Second law I 2.1 Entropy as a State Function(3) P1 P2 V1 V2 1 2 Pressure Volume Lost work Actual work P1 P2 V1 V2 1 2 Pressure Volume Reversible work ∫ = − 21VV W PdV A, reversible B, irreversible
2.1 Entropy as a State Function(4) ww S.J.T.0. Phase Transformation and Applications ds Or=80-8Wre +W =80-8lw T dS= Elw T T Isothermal V SJTU Thermodynamics of Materials Fall 2012 ©X.J.Jin Lecture 3 Second law I
Phase Transformation and Applications S. J. T. U. SJTU Thermodynamics of Materials Fall 2012 © X. J. Jin Lecture 3 Second law I 2.1 Entropy as a State Function(4) T Q dS δ rev = δQrev = δQ −δWrev +δW = δQ −δlw T lw T Q dS δ actual δ = − Isothermal