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.Themolarheat

2、capacityCPofleadmaybetakenas29.3J/(molK)Solution:1.2whatistheaveragepowerproductioninwattsofapersonwhoburns2500kcaloffoodinaday?Estimatetheaverageadditionalpowderproductionof75Kgmanwhoisclimbingamountainattherateof20m/minSolution1.3Onecubicdecimeter(1dm3)ofwaterisb

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

4、ne/cm2)isalsousedforsurfacetensiondyn/cm)Solution1.4Gaseousheliumistobeusedtoquenchahotpieceofmetal.Theheliumisinstorageinaninsulatedtankwithavolumeof50Landatemperatureof25℃,thepressureis10atm.Assumethatheliumisanidealgas.(a)whenthevalveisopenedandthegasescapesinto

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

6、tedtankissurroundedbyaverylargevolume(assumeinfinitevolume)ofanidealgasatatemperatureT0.Thevalveonthetankisoðenedandthesurroundinggasisallowedtoflowsuicklyintot(etankuntilthepressureinsi`ethetankisequalsthepressureoutside.Assumethatnoheatflowtakesplace.Whatisthe0fi

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

8、tetheheatofreactionofmethanewithoxygenat298K,assumingthattheproductsofreactionareCO2andCH4(gas)[Thisheatofreactionisalsocalledthelowcalorificpowe