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.ThemolarheatcapacityCPofleadmaybetakenas29.

2、3J/(molK)Solution:1.2whatistheaveragepowerproductioninwattsofapersonwhoburns2500kcaloffoodinaday?Estimatetheaverageadditionalpowderproductionof75Kgmanwhoisclimbingamountainattherateof20m/minSolution1.3Onecubicdecimeter(1dm3)ofwaterisbrokenintodropletshavingadiameterofonemicrometer(1um)at20℃.(a)w

3、hatisthetotalareaofthedroplets?(b)Calculatetheminimumworkrequiredtoproducethedroplets.Assumethatthedropletsarerest(havezerovelocity)Waterhaveasurfacetensionof72.75dyn/cmat20℃(NOTES:thetermsurfaceenergy(ene/cm2)isalsousedforsurfacetensiondyn/cm)Solution1.4Gaseousheliumistobeusedtoquenchahotpieceo

4、fmetal.Theheliumisinstorageinaninsulatedtankwithavolumeof50Landatemperatureof25℃,thepressureis10atm.Assumethatheliumisanidealgas.(a)whenthevalveisopenedandthegasescapesintothequenchchamber(pressure=1atm),whatwillbethetemperatureofthefirstgastohitthespecimen?(b)Astheheliumflows,thepressureintheta

5、nkdrops.Whatwillbethetemperatureoftheheliumenteringthequenchchamberwhenthepressureinthetankhasfallento1atm?Solution:1.5Anevacuated(P=0),insultedtankissurroundedbyaverylargevolume(assumeinfinitevolume)ofanidealgasatatemperatureT0.Thevalveonthetankisoðenedandthesurroundinggasisallowedtoflowsuickly

6、intot(etankuntilthepressureinsi`ethetankisequalsthepressureoutside.Assumethatnoheatflowtakesplace.Whatisthe0finaltempeturekftèegaSinthetank?Theheatcap!citymfthegas,CpandCveachíaybe(assumedtobec/nsuantoverthåtemperaturerang!spanNedbythedøperiment.YouanswermaybemeftintermsofCpandSvMhint:onewayto

7、approachthexroblemistodefinethesystemasthegasendsupinthetank.solution1.6Calculatetheheatofreactionofmethanewithoxygenat298K,assumingthattheproductsofreactionareCO2andCH4(gas)[Thisheatofreactionisalsocalledthelowcalorificpowe