绝热不可逆鼓胀 Q=0 ∆U=Q-W ∆U=-W
Cv(T2-T1)=-P外（V2-V1)
3/2R*3(T2-400)+5/2R*2(T2-400)=100000(5RT1/P1-5RT2/P2)
P1=200KPa P2=100KPa
解得T2=331K
W=P外（V2-V1)=100000（nRT2/P2-nRT1/P1)=100000(5*8.314*331/100000-5*8.314*400/200000)=5.45KJ
∆U=-5.45KJ
∆H=Cp(T2-T1)=5/2*8.314*3(331-400)+7/2*8.314*2(331-400)=-8.32KJ