Test Bank for Elements of Physical Chemistry 7th Edition Atkins

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Testgbank:gFocusg02

Type:gmultiplegchoicegquestiongTit
le:gFocusg02g-gQuestiong01
01) Calculategthegexpansiongworkgdonegongthegsystemgwhengexactlyg1gmolgofgsolidgammoni
umgchloride,gNH4Cl,gdecomposesgcompletelygtogyieldggaseousgammonia,gNH3g andghydroge
ngchloride,gHClgatgagtemperaturegofg1250gK.g Treatgthegexpansiongasgirreversiblegandgthegg
asesgformedgasgperfect.
Feedback:gThegworkgdonegongagsystemgwhengitgexpandsgagainstgagconstantgpressuregisggi
vengbygeqng2A.1a
𝑤g =g −𝑝exΔ𝑉
Thegdecompositiongofgexactlyg1gmolgofgsolidgammoniumgchloride
NH4Cl(s)g→gNH3(g)g+gHCl(g)gyieldsg2gmolgofggas.g Wegmaygassumegthatgthegvolumegofgth
egsolidgammoniumgchloridegisgnegligiblegingcomparisongwithgthegvolumegofgtheggasgproduc
ed.gThegchangegingvolumegongdecompositiongisgtherefore
Δ𝑉g =g𝑉fg −g𝑉ig ≈g𝑉f
Treatinggtheggasgasgperfect,gsogtha
t 𝑛𝑅𝑇
𝑉fg
𝑝ex
=
then
𝑛𝑅𝑇
𝑤g =g −𝑝exg ×
𝑝ex
=g −𝑛𝑅𝑇
=g −(2.00gmol)g×g(8.3145gJgK−1mol−1)g×g(1250gK)
=g −20.8g ×g103J
=g −𝟐𝟎.g𝟖g𝐤𝐉
Pagegreference:g41
a. –15.4gkJ
b. –4.96gkJ
c. –16.6gkJ
*d.g–20.8gkJ

Type:gmultiplegchoicegquestiongTit
le:gFocusg02g-gQuestiong02
02) Calculategthegheatgtransferredgtogthegsystemgwheng1.00gmolgofgagperfectggasgexpa
ndsgreversiblygatgagconstantgtemperaturegofg25°Cgsogthatgitsgvolumegdoubles.
Feedback:gForgthegisothermalgexpansiongofgagperfectggas,geqng2B.4gshowsgthatgthegheatgtra
nsferredgandgworkgdonegaregrelatedgby
𝑞g =g −𝑤
andgso,gusinggeqng2A.2gforgagreversiblegexpansion,gwegobtaingeqng2B.5,
𝑞g =g −𝑛𝑅𝑇𝑙𝑛𝑉f/𝑉i
Forgthisgexpansion,
𝑉f/𝑉ig =g2
sogthat
𝑞g =g −(1.00gmol)g×g(8.3145gJgK−1mol−1)g×g(273g+g25)Kg×glng2
=g −1.72g×g103J
=g −𝟏.g𝟕𝟐g𝐤𝐉g𝐦𝐨𝐥−𝟏
Pagegreference:g43,g51
a. –144gJ
b. –746gJ
*c.g–1.72gkJgmol–1
d.g2.48gkJ

Type:gmultiplegchoicegquestiongTit
le:gFocusg02g-gQuestiong03
08)gThegconstantgpressuregmolargheatgcapacitygofgzincgisg25.40gJgK–1g mol–
1g atg298gK.gCalculategthegconstantgpressuregspecificgheatgcapacitygofgzincgatgthisgtempera




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Feedback:gSpecificgheatgcapacitygisgdefinedgasgthegheatgcapacitygpergunitgmassgofgsample
𝐶sg =g 𝐶/𝑚
andgso,
𝐶sg =g𝐶𝑝,m/𝑀
Forgzinc,gthegmolargmassgi
𝑀g =g 65.37gggmol−1
sgsogthat
𝐶sg =g𝐶𝑝,m/
𝑀
=g (25.40g JgK−1mol−1)g/g(65.37g ×g10−3kggmol−1)
=g 𝟑𝟖𝟖.g𝟔g𝐉g𝐊−𝟏𝐤𝐠−𝟏
Pagegreference:g48
a. 1.660gkJgK–1g kg–1
*b.g388.6gJgK–1g kg–1
c. 17.09gJgK–1g kg–1
d. 33.71gJgK–1g kg–1

Type:gmultiplegchoicegquestiongTit
le:gFocusg02g-gQuestiong04
03) Thegmolargheatgcapacitygofgsolidgaluminiumgisg24.4gJgK–1g mol–
1g atg25°C.g Calculategthegchangeginginternalgenergygwheng1.00gmolgofgsolidgaluminiumgisg

heatedgfromgagtemperaturegofg20°Cgtog30°C.
Feedback:gHeatgcapacitygisgdefinedgbygeqng2C.4agandgsogwegcangwrite
∆𝑈g =g 𝐶𝑉Δ𝑇
Forgagsolid,
𝐶𝑝g ≈g 𝐶𝑉
andgsogwegdognotgneedgtogworrygaboutgthegdistinctiongbetweengthegheatgcapacitygatgconstant
gvolumegandgpressure.g Wegmaygalsogreasonablygassumegthatgthegheatgcapacitygdoesgnotgva
rygovergthegrangegofgtemperature.g Agchangegingtemperaturegfromg20g°Cgtog30g°Cgmeans

Δ𝑇g =g +10gK
Thus
Δ𝑈g =g 𝑛𝐶mΔ𝑇
=g (1.00gmol)g ×g(24.4gJgK–1mol−1)g×g(10g K)
=g 𝟐𝟒𝟒g𝐉
Pagegreference:g54
*a.g244gJ
b. 24.4gJ
c. 171gJ
d. 327gJ

Type:gmultiplegchoicegquestiongTit
le:gFocusg02g-gQuestiong05
04) Thegconstantgpressuregmolargheatgcapacitygofgammonia,gNH3,ghasgbeengfoundgtogvaryg
withgtemperaturegaccordinggtogthegrelation
𝐶𝑝,mg /gJgK−1mol−1g =g 𝑎g +g𝑏𝑇g +g𝑐/𝑇2
withgag=g29.73,gbg=g25.1gg10–3g K–1g andgcg=g–
1.55gg105g K2.g Calculategthegvaluegofgthegconstantgpressuregmolargheatgcapacitygatg25.0g°C.
Feedback:gThegconstantgpressuregmolargheatgcapacitygmaygbegcalculatedgbygdirectgsubst
itution.g Wegmust,ghowever,gremembergtogconvertgthegtemperaturegtogunitsgofgkelvin.gThus
𝑇g =g (273.15g+g25.0)Kg =g 298.15gK
sogthat
𝑐
𝐶𝑝,m /(gJgK mol )g =g 𝑎g +g𝑏𝑇g +g2
−1 −1
𝑇
=g 29.73g+g{(25.1g×g10−3g K−1)g×g(298.15gK)}g−g{1.55g×g105g K2/(298.15gK)
2}

=g 35.47




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