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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

17

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e.g.Estimate Hvap @T2 when Hvap @T1 known

18

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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

22

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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

24

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e.g.Horxn calc.

25

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4.5StandardHeatofom us on

26

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Combustionrxns easilycarriedincalorimeter

serve e erm n ng f compoun s

e.g.P139

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e.g.Horxn fromheatofcombustion

28

Suggestedprob.:4.19;4.20;4.24;4.26

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4.6TemperatureDependenceofrxn

29

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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

33

. . . . .