du s tds- pdv du+ d(Pvs- Pdv+Pdv +VdP d(U+PV)≤Tds+vdP dHs tds +VdP HEU+PV 在P固定时:dH≤0,或H=Hmin H(SP)热力学势函数dU  TdS - PdV 在S,P固定时： dH  0, 或 H = Hmin dU + d(PV) TdS – PdV +PdV +VdP d(U + PV) TdS +VdP dH TdS +VdP H = U +PV H(S,P) -热力学势函数 焓