中国石油大学物理化学历年考研计算题(3)

2020-05-23 14:24

答案;1

① p1V1?nRTT p2/p1?T2/T1 T2?p2T1/p1=250 K 1 p2V2?nR21??1??1??② T3p3??T2p2? T3?T2???p2???p?3???50??250???100??1?1.41.4?304.75K

③ Q?Q1?Q2?Q1?nCV,m(T2?T1)?4?2.5?8.314?(250?750)??41570J

?U?nCV,m(T3?T1)?4?2.5?8.314?(304.75?750)??37018J ?H?nCp,m(T3?T1)?4?3.5?8.314?(304.75?750)??51825J ?S??S1?nCV,mlnT2250?4?2.5?8.314?ln??91.34J·K?1 T1750④ ?G??H??(TS)??H?(T3S3?T1S1)

?S0?nCp,mlnpT1?nRln0?292.80?13.48?279.30J·K?1 T0p1?1 S1?S0??S0?4S???S?4?191.6?279.30?1045.12J·K0mS3?S1??S?954.38J·K?1

?G??H?(T3S3?T1S1)=-51825-(304.75×945.38-750×1045.12)=441168 J

2解:反应:C2H6(g)= C2H4(g)+ H2(g)

?mol (1) ?rHm=52.26+84.68=136.94kJ·?1?mol?1·K?1 =219.56+130.684-229.60=120.644J·?rSm???mol?1>0,=?rHm-T?rSm=136940-298×120.644=100988J·不能自发进行 ?rGm???rGm(2) ?rGm??RTlnK K?exp???RT??????18? ?1.985?10??11

(3) 425 K时,?G????1rm=?rHm-T?rSm=136940-425×120.644=85666J·mol K??exp??85666??11??8.314?425???2.957?10

3解:(a) ??-1vHm=33.273 kJ·mol

Q=△H=33.273 kJ

W=-p△V=-RT=-8.314×383.15=-3185.5 J △U= Q+W=30.087 kJ·mol-1

△S=△H/T=33273/383.15=86.84 J·K-1 △G=0

(b) △U, △H, △S,△G均同(a)

4

?Hm(268)=?H=?H1+?H2-?H3=?Hm(278.5)+ [C??p,m(l)-Cp,m(s)][278.5-268]

= 9956+(127.3-123.6)×10.5=9994.85 J/mol

?Sm(268)=?S=?S1+?S2-?S3=

9956278.5+ [C?p,m(l)-C?278.5p,m(s)]ln268 = 35.85 J·K-1·mol-1

5解: 惰性气体为单原子,

T不变,?U=?H=0

W=nRTln

p2p=-5743 J 1Q=-W=5743 ?S=

Q=19.14 J.K-1 T?G=?A=-T?S=-Q=5743 J

6解:(1)p=nRT5?8V=.314?37310=1551Pa

12

(2)

?H=?H1+?H2=?H1=5×40.64kJ=203.2 kJ W=0

?U=?U1+?U2=?U1=?H-?(pV)= ?H-nRT=203.2-5×8.314×373×10-3=187.7kJ Q=?U=187.7kJ

7解: He为理想气体 T不变,?U=?H=0

W=nRTln

p2=2305 J p1Q=-W=-2305 J ?S=

Q=-5.76 J.K-1 T?G=?A=-T?S=-Q=2305 J

8解:(1)比较式: ln p0=-

?H+C lnp0=19.434-1568/T RT ?vapHm=1568R=13036 J.mol-1

(2)同理升华焓 ?subHm=1975R=16420 J.mol-1 (3)熔化焓?fusHm=?subHm-?vapHm=3384 J.mol-1

(4)三相点的温度下:固态的蒸汽压=液态的蒸汽压

19.434-1568/T=23.136-1975/T 解得温度:T=110K

9解:绝热恒压

(A)1mol水由30℃→100℃需吸热:Q1=1×76×(100-30)=5320 J 3mol水蒸气由150℃→100℃放热:Q2=3×33×50=4950 J Q2

5320?4950=9.107×10-3mol

40630最终体系的平衡相态为100℃,有水1.0091mol,有水蒸气2.9909mol, (B)体系的终态温度为100℃ (C)绝热恒压,?H=0

?S= ?S1(1mol水30℃→100℃)+?S2(3mol水蒸气150℃→100℃)

+?S3(9.107×10-3mol水蒸气→水)

13

?H373373 =nC(水)ln303+ nC水气)lnvapmp,mp,m(423-?n373

=15.769-12.454-0.992=2.35 J.K

-1

10解:(A) 1摩尔理想气体300K由30 L恒温可逆膨胀至100 L

?U=0 W=-nRT ln

V2V=-3003 J 1 Q=-W =3003 J ?S= Q/T=10.01 J.K-1

(B) 问真空膨胀是不可逆过程;?U、?S同(A),Q=0 ,W=0 11解:在101.325kPa下

?S= ?S1+ ?S2+ ?S3

?S3731=Cp,m,Lln

298=75.291 ln 373298=16.902 J.K-1 ?S?H406902= T=373=109.088 J.K-1

?S4234233= Cp,m,gln 373=35.58 ln 373=4.476 J.K-1

?S=130.466 J.K-1

W=-p?V=-pVg=-nRT2=-1×8.314×423=-3516.8 J

?H= ? H 1+ ? H 2+ ? H 3=75.291×(100-25)+40690+35.58×(150-100)=48116 J

12解:(1) lnp2?p?H??1?1??1R??T1T2?? 对苯(A):lnp3135.06??H?1R??363?1?178.65?H?11?368??① ln135.06?R??363?373??②

式①/式②得:p?3?pA?155.6kPa 对氯苯(B):lnp327.73??H?11?39.06?H?11?R??363?368??③ ln27.73?R??363?373??④ 式③/式④得:p?3?pB?33.0kPa

14

?33.0xBpBpBxB(2) 此时 yB?0.3000?= ???pA?pBpA(1?xB)?pBxB155.6(1?xB)?33.0xB? 得: xB?0.67 p?p? (1?x)?pABBxB?73.8kPa?(3) 此时 xB?0.3000 p?p? 97kPaA(1?xB)?pBxB?10.yB?pB33.0?0.3??0.09

pA?pB109.713解:(a) 苯为溶剂A: pA=p?1?xB?=10.01×(1-0.0385)=9.6246 kPa A?pB=yB=1-0.095 pB=91.687 kPa

pA?pBp=pA+pB=9.6246+91.687 =101.31 kPa

(b) pB=kBxB kB=pB/xB=2381 kPa 14解:CS2(B)和CH3COCH3(A)体系,

aA=

aApApyA= =,对B的公式类推(B代替A即可) ?A**xApApAp2?VHm=

Rp1?11????TT??

2??1-1

纯组分的蒸气压用克-克方程计算:ln对CH3COCH3(A):T1=329.7K p1=101.325kPa T2=317.5K ?VHm=32370 J.mol 得 p2=pA=0.6352×101.325kPa

对CS2(B):T1=319.7K p1=101.325kPa T2=317.5K ?VHm=27780 J.mol 得 p2=pB=0.9301×101.325kPa

*-1

*aA=

pyA0.620.9761==0.9751 ==1.220 ?A0.63521?0.2p*ApyB0.380.4086?==0.4086 ==2.043 A*0.2pB0.930111 , nB=-1=0.111mol

0.91?nBaB=

15解:(A) 在1molA中加入nBB,xA(α相)=0.9=

(B) xA(β相)=0.1 ,xA(α相)=0.1=

1 ,nB=9mol

1?nB 15


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