南昌大学材料热力学答案

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1、Theproblemsofthefirstlaw1.1aleadbulletisfiredatafrigidsurface.Atwhatspeedmustittraveltomeltonimpact,ifitsinitialtemperatureis25℃andheatingoftherigidsurfaceoftherigidsurfaceisneglected?Themeltingpointofleadis327℃.Themolarheatoffusionoftheleadis4.8kJ/mol.Themolarhea

2、tcapacityCPofleadmaybetakenas29.3J/(molK)Solution:1.2whatistheaveragepowerproductioninwattsofapersonwhoburns2500kcaloffoodinaday?Estimatetheaverageadditionalpowderproductionof75Kgmanwhoisclimbingamountainattherateof20m/minSolution1.3Onecubicdecimeter(1dm3)ofwateri

3、sbrokenintodropletshavingadiameterofonemicrometer(1um)at20℃.(a)whatisthetotalareaofthedroplets?(b)Calculatetheminimumworkrequiredtoproducethedroplets.Assumethatthedropletsarerest(havezerovelocity)Waterhaveasurfacetensionof72.75dyn/cmat20℃(NOTES:thetermsurfaceenerg

4、y(ene/cm2)isalsousedforsurfacetensiondyn/cm)Solution1.4Gaseousheliumistobeusedtoquenchahotpieceofmetal.Theheliumisinstorageinaninsulatedtankwithavolumeof50Landatemperatureof25℃,thepressureis10atm.Assumethatheliumisanidealgas.(a)whenthevalveisopenedandthegasescapes

5、intothequenchchamber(pressure=1atm),whatwillbethetemperatureofthefirstgastohitthespecimen?(b)Astheheliumflows,thepressureinthetankdrops.Whatwillbethetemperatureoftheheliumenteringthequenchchamberwhenthepressureinthetankhasfallento1atm?Solution:1.5Anevacuated(P=0),

6、insultedtankissurroundedbyaverylargevolume(assumeinfinitevolume)ofanidealgasatatemperatureT0.Thevalveonthetankisoðenedandthesurroundinggasisallowedtoflowsuicklyintot(etankuntilthepressureinsi`ethetankisequalsthepressureoutside.Assumethatnoheatflowtakesplace.Whatis

7、the0finaltempeturekftèegaSinthetank?Theheatcap!citymfthegas,CpandCveachíaybe(assumedtobec/nsuantoverthåtemperaturerang!spanNedbythedøperiment.YouanswermaybemeftintermsofCpandSvMhint:onewaytoapproachthexroblemistodefinethesystemasthegasendsupinthetank.solution1.6

8、Calculatetheheatofreactionofmethanewithoxygenat298K,assumingthattheproductsofreactionareCO2andCH4(gas)[Thisheatofreactionisalsocalledthelowcalorificpowe