材料热力学 习题答案

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

2、tyCPofleadmaybetakenas29.3J/(molK)(1.1)Solution:2.whatistheaveragepowerproductioninwattsofapersonwhoburns2500kcaloffoodinaday?Estimatetheaverageadditionalpowderproductionof75Kgmanwhoisclimbingamountainatehrateof20m/min(1.2)Solution3Onecubicdecimeter(1dm3)ofwaterisbroken

3、intodropletshavingadiameterofonemicrometer(1um)at20℃.(1.3)(a)whatisthetotalareaofthedroplets?(b)Calculatetheminimumworkrequiredtoproducethedroplets.Assumethatthedropletsarerest(havezerovelocity)Waterhaveasurfacetensionof72.75dyn/cmat20℃(NOTES:thetermsurfaceenergy(ene/cm

4、2)isalsousedforsurfacetensiondyn/cm)Solution4.Gaseousheliumistobeusedtoquenchahotpieceofmetal.Theheliumisinstorageinaninsulatedtankwithavolumeof50Landatemperatureof25℃,thepressureis10atm.Assumethatheliumisanidealgas.(a)whenthevalveisopenedandthegasescapesintothequenchch

5、amber(pressure=1atm),whatwillbethetemperatureofthefirstgastohitthespecimen?(a)Astheheliumflows,thepressureinthetankdrops.Whatwillbethetemperatureoftheheliumenteringthequenchchamberwhenthepressureinthetankhasfallento1atm?(1.4)Solution:5Anevacuated(P=0),insultedtankissurr

6、oundedbyaverylargevolume(assumeinfinitevolume)ofanidealgasatatemperatureT0.Thevalveonthetankisopenedandthesurroundinggasisallowedtoflowquicklyintothetankuntilthepressureinsidethetankisequalsthepressureoutside.Assumethatnoheatflowtakesplace.Whatisthefinaltempetureofthega

7、sinthetank?Theheatcapacityofthegas,CpandCveachmaybeassumedtobeconstantoverthetemperaturerangspannedbytheexperiment.YouanswermaybeleftintermsofCpandCvhint:onewaytoapproachtheproblemistodefinethesystemasthegasendsupinthetank.(1.5)solution6.Calculatetheheatofreactionofmeth

8、anewithoxygenat298K,assumingthattheproductsofreactionareCO2andCH4(gas)[Thisheatofreactionisalsocalledthelowcal