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8/4/2019 ENCH427 L3-Heat Effects
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Thermodynamics
Dr.Maen Husein. . .L3:HeatEffects
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HeatEffects
Puresubsormixture Ch.4 HeatofMixing:Mixture{Ch12}
ea o :
Mixture{Ch.
4}
2
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. ens e ea ec s
3
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, ,formation/separationofsolutions(Ch12)
Forpuresubs(orhomogeneoussysof
,
4
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ForV=const rocess re ardlessofsubs ForUf(V)(regardlessofprocess):Truefor
incompressibleliq &solids
5
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Also,forsinglephasepuresubs(or
H=H(T,P)
=
ForHf(P)(regardlessofprocess):Trueforideal as real as low ressures & solids*
6
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C &CV=f(T)
for
a
given
subs*,
or
ideal
gas,
empirical:
A,B,C,etc=f(gas/subs)
7
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Cig
=f T as im ortant 1st
calcthermo ro foridealgas;2nd correctforrealgas
molecularstructure(statisticalmechanics)
{beyond
our
scope}
Parameters:TableC.1
8
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Cpig=f(T,gas):
Increase
smoothly
to
upper
limit(modesofmolecular
motion(?)fullyexcited)
CPig isgasdependent,since
even un er ea con t ons,
molecularstructurereflectsonproperties
9
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C idealgasmixture,liq &solids Const.compositiongasmixtures puresubs
Cpig
mixtureideal
gases:
n(4.4)(Tables C.2&C.3)ORcorrelation(Perrys
10
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Evaluationsensibleheatintegral
where
OR
whereCPH isanaverageCp calcfromtheintegral
IfTunknown iterationmakesusof:11
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e.g.useCPig
12Suggestedprob.:4.2;4.3;4.6;4.8
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4.2LatentHeatofPureSubsWARNING: P133,2ND PARA:ITISNOTTHEINTENSIVESTATE
p ys ca c angesOFTHESYSTEMWHICHISDETERMINED,BUTRATHERTHE
INTENSIVESTATEOFEACHPHASEINEQUILIBRIUM.
13
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=
T=const);ClausiusClapeyron Eqn (derivedCh6):satsat
(4.11))(TdVTHVTTd
sat
slopefromPT
dia ramsforthe ivenT
)(Td
Evaporation:
14fv
vap
HHH fv
vap
VVV
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H
phase
change
estimated
from:
1)
Clausius
Clapeyron Eqn;2)measuredcalorimeter;3)
correlation H=(T;material)
H@TofinterestmightnotbeavailableUNIVAP rovidesalternative notcovered
Ofinterest:1) Hvap @Tn (1atm)vapnH. oug es ma e: rou on s ru e :
1.2)Moreaccurate:Riedelseqn*:
~nRT
(4.12)930.0
)013.1(ln092.1 Cvap
n
T
P
RT
H
Pc criticalP[=]bar; reducedTatn.b.p.(?) 15
n
nrT
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e.g.Ridiel eqn
SuggestedProb:4.10;4.12;4.14 16
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contdofinterest:2)Estimate Hvap @T2*
when Hvap @T1*isknown(fairlyaccurate)
38.0
(4.13)112
1
2
r
r
vap
vap
TH
H
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e.g.Estimate Hvap @T2 when Hvap @T1 known
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4.3StandardHeatofRXNc em ca c anges
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Energycontentreactant>energycontentproduct Heatreleased Hrxn (viseversa)
Collection Hrxn ofallrxns impossible calc Hrxnfromrxn carriedinstandardwaymindata
orag venrxn, rxn= reac an s pro uc s
Standardize:sameTforreactants&products 20
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Standardheatofrxn Hrxn
oenthalpychangewhenamolesofAreactwithbmolesofBintheirSTDstateatagivenT toproducemolesofL
T
STDstateofspeciesatagivenT=f(P,composition,
PSTD 1atm;morerecent 1bar
State:1) gas idealgasgasesseldomdeviatefromidealit 1 bar 2 li &solid real
STD
state=f(T) 21
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. an ar ea o orma on
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Horxn =i(Hof)i
i stoichiometric coefficient(+ve product; vereactant){usebalancedeqn only}
Hof
formationrxn ofcompound:rxn forms1moleofcompoundstartingfromitscons uen e emen s
H
o
f298 tabulated(Table
C.4).
Ifrxn @
different
,sens e ea orreac an s pro uc s, sused
aw ac a ss a e unc on ess slawapplies:rxns &Horxn canbeadded
23
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Ho element 0 convenience*since:
1)ifreactants&productsarecompoundssamemolesofanelementwillappearonbothsideswhileusingHessslaw eliminate
2) ifareactantoraproductisanelementenergyrelativetotheelementisaccounted
for
in
of
the
H
o
f compound Stateofelement compoundindicatedinthe
rxn equation
DifferencebetweenisHof,H2O(l) & Hof,H2O(g) ~Hvap298K
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e.g.Horxn calc.
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4.5StandardHeatofom us on
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Combustionrxns easilycarriedincalorimeter
serve e erm n ng f compoun s
e.g.P139
27
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e.g.Horxn fromheatofcombustion
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Suggestedprob.:4.19;4.20;4.24;4.26
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4.6TemperatureDependenceofrxn
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Horxn=f(T)only dependenceofHo
rxn onTcan
.
oo
o H
T
PPTrxn
T,
oo
o
P
oo
Trxn dTCHH298
298,
iPiP ,
TheaboveanalysisimpliesthatanychangesofHorxn fromreferenceTarecapturedbysensible
.
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Integralevaluatedasbelow
ORusingmeanCP:
)298(298, TCHH
o
P
oo
Trxn
31
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4.7HeatEffectsofIndustrials
32
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e.g.IndustrialRXNs
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. . . . .
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