225_Module 03 - Chemical Thermodynamics_2015presented-4

8/9/2019 225_Module 03 - Chemical Thermodynamics_2015presented-4

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Module 3

Chemical Thermodynamics Thermodynamics Fundamentals (Ch. 1.4)

First Law of Thermodynamics

System Definition Energy alance

Enthal!y

S!ecific "eat

Second Law of Thermodynamics

Entro!y

Third Law of Thermodynamics

#$solute %ero Chemical Thermodynamics (Ch. &.1'&.)

i$$*s Free Energy (+ot in te,t$oo-)

an 1/ &01


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Chemical Thermodynamics

2hy is this to!ic im!ortant inenvironmental engineering?

#nswers to the following3

2ill heat $e gien off or a$sor$ed $y a system5 2hat will $e the tem!erature changes associated with

the heat transfer5

2ill a reaction occur without addition of e,ternal energy5

"ow do we -now whether final/ sta$le (e6uili$rium)conditions hae $een esta$lished5


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Chemical Thermodynamics

2hy is this to!ic im!ortant inenvironmental engineering?

#!!lications such as

7ncineration Com$ustion

Chemical handling

Thermal !ollution studies 8!timi9ing the energy efficiency of !lants

:any others


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Energy Conseration and System Definition

Energy cannot $e created or destroyed 7t can only change forms

;rinci!le of conseration of energy

#nalysis on a physico-chemical system

(similar to a control olume)

8utside of the chemical system3 surroundings

Open system3

matter and energy can cross system*s $oundaries Closed system3

only energy can cross system*s $oundaries

Isolated system3

nor matter neither energy can cross system*s $oundaries


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nergy !alance

For a !hysico'chemical system/ we can write and energy

$alance including 6uantities

"eatthat entered the system (Qin) nergyaccumulated in the system (E)

#or$!erformed on the surroundings $y system (Wout)

Total energy (E) includes3

< internal %U&3 Tem!erature (moement of molecules)< $inetic %KE&' :oement of the system< potential %PE&'raitational eleation of system

(ystem

outin WQPEKEUE =++=

outin WQE =EinQ outW


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nthalpy )efinition

nthalpy %H&

Thermodynamic !otential (amount of

wor- o$taina$le from a system)

Sum of internal energy (U) and the

!ressure !otential (PV)

E,!eriment

#dd heat while maintaining constant

!ressure Tem!erature will increase

=olume will increase

y moing the !iston u!/ the system is

using the heat !roided to do wor$

(T*T +

P= 1 atmT= 20C

P= 1 atmT= 40C

(T*T ,

PVUH +=


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oundary wor-3

nthalpy )efinition

(T*T ,

(T*T +( ) 1212 UUVVPQin =

( ) ( )1122 PVUPVUQin++=

12 HHQin =

VPUH +=

PEKEUWQoutin

++=

UWQ outin =

( )12

2

1

VVPPdVW

V

Vout

==


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Change in nthalpy %H&3 6uantity of heat

a$sor$ed $y a system at constant ;

Total enthal!y (H) of a system difficult to

measure

7nterested in the changein enthal!y/ not thea$solute alue

+eed reference !oint

Trac$ing the nthalpy of a (ystem

VPUH +=


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Module 3

Chemical Thermodynamics Thermodynamics Fundamentals (Ch. 1.4)


System Definition Energy alance

Enthal!y S!ecific "eat

Second Law of Thermodynamics

Entro!y


#$solute %ero Chemical Thermodynamics (Ch. &.1'&.)

i$$*s Free Energy (+ot in te,t$oo-)

an 1/ &01


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nthalpy Change of a Chemical eaction

and )efinition of (tandard Conditions

(tandard reference state3 &oC (&>?@)/ andreactants and !roducts at 1 atm for gases or 1 molAL for solutes

Standard enthal!y of elements B 0

Standard enthal!y of a com!ound3 heat of reaction $y which it is

formed from its elements

Change in "eat of reaction (H) B

(enthal!ies of the reaction !roducts H, stoichiometric coeff.)

(enthal!ies of the reactants H , stoichiometric coeff.)

EDBA edba ++


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Data on standard enthal!ies of formation at

standard conditions aaila$le from

e,!eriments (results in ta$les)

Com$ustion of methane gas (natural gas)3

nthalpy Change of a Chemical eaction

at (tandard Conditions

./0124+ 54+ .36314+ .,0+124,

)O(H2)(CO)(O2)(CH 2224 gggg ++

)85.74()8.241(2)5.393(0298 +=H

methaneofkJmo!3.8020298 =H

0298H


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(pecific "eat )efinition

(pecific "eat %C&'energy re6uired to raise

the tem!erature of a unit mass of asu$stance $y one degree - A -g 0C

constant !ressure

< Qinor H3 heat in!ut(for a solution/ it can $e from chemical reaction)

< m3 mass of material a$sor$ing energy

(immediate surrounding solution is mainly "&8)

< T3 change in tem!erature

Tm

QC inp = Tm

HCp

=


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Change in "eat of a (olution 7y Chemical eaction

Solution3 7mmediate surrounding water

Geaction system

+HH

queendothermiH

ueexothermiqH

edba

#

#

EDBA

+

++


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Systems moe from highly orderedtomore randomstates

Systems moe towards e6uili$rium (minimum energy state)

2or- is re6uired to create order

+eed to measure order3 entro!y ()

Entro!y increases with disorder

(econd Law of Thermodynamics

Low Entro!y "igh Entro!y

D$ff%&$on an$mat$on# htt'#.o%t%*e.+omat+h,

-/B$02e-Hh1feat%e'!ae4eta$!'a0e


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#hat is ntropy %S&?

Entro!y is a measure of molecular disorder/ ormolecular randomness

Hncertainty a$out the !ositions of molecules at

any instant


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nergy Organiation vs #or$' ntropy %S&

Disorgani9ed energy cannot $e used to do wor-


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nergy Characteristics' @uantity and @uality

Iuantity of energy always !resered (1stLaw)

Iuality of energy always decreases (&ndLaw)

i.e./ entro!y increases

+5 $A

8erall system*s

entro!y increases

Constant


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Third Law'entro!y is 9ero at a tem!erature of

a$solute 9ero

:olecules motionless

State of ultimate molecular order

+o uncertainty a$out !osition of molecules


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# reaction will !roceed spontaneouslyonly if

the !rocess leads to a decrease in the free

energy of the system ( J 0)

Ks!ontaneously*3 without energy $eing

added to the system

#hat is the se of Bi77s Free nergy?

* !1) J 0

&) M 0

) B 0

* !

* !

e6uili$rium

driing

force5


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Change in free energy during a reaction

#hat is the se of Bi77s Free nergy?

FreeEnergy

Geactants ;roducts

*

!

C )

F


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Free energy cannot $e measured directly

(tandard reference state3 &oC/ and

all reactantsA!roducts at 1 atm for gases or 1 molAL for solutes

Standard free energy of elements B 0

Standard free energy of a com!ound (0) B free energy of

formation from its elements

Change in standard free energy for a reaction3

Change in Bi77s Free nergy of a eaction

at (tandard Conditions

oB

(free energy of the reaction !roducts , stoichiometric coeff.)

' (free energy of the reactants , stoichiometric coeff.)


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*cid rain3 result of $urning fossil fuels

#ill These eactions Droceed?

Fossil

fuel

S8&

Com$ustion

"&

S8

Dissoles in water dro!lets in atmos!here

"&S84

8,idation $y o,ygen or !ero,ide/

cataly9ed $y Cu or Fe in cloud water


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Changing From


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Changing From

(tandard Conditions to Field Conditions For nonstandard conditions (!)3

eaction @uotient %@&

67# 8hemo4nam$+ A+t$-$t 9mo!:;&o!%te&

o

9'at$a! 'e&&%e $n atm;0a&e&

< = (a+t$-$t +oeff$+$ent)

{ } { }

{ } { }

+=

ba

d%

o

&'

(C)T!! !n

D+C*BaA ++

( )(>)etem'eat%A*&o!%te#

mo!

kJ103143.8+on&tanta&?ea!#

+on$t$on&&tanafo#

enefee&@$**$nChane#

3

TK

)

!!

!

o

=

Thermodynamic )efinition of


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For nonstandard conditions (!)3

Thermodynamic )efinition of

=uili7rium Constant %E&

#t e6uili$rium/

=uili7rium constant %E&

[ ] [ ]

[ ] [ ]

+=

ba

d%

o

&'

(C)T!! !n

D+C*BaA ++

[ ] [ ]

[ ] [ ]

=

ba

d%

o

&'

(C)T! !n

(atm)'e&&%e'at$a!a&o(mo!:)$on+on+entat&o!%te

#ill These eactions Droceed In The Field?


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#ill These eactions Droceed In The Field?S8&(g)

"&S8(a6)

"&S84(a6)

m*ppm+

mo",-!#H#H# oaq"g

0285.00.150

0.3)(32)(2)(2 +=+

m*atmm*

mo",-!#H##H oaq$eCu

gaq

028.021.0028.0

5.210)(42

)(221

)(32 = +

[ ][ ][ ]

+=

)(2)(2

)(32!n

"g

aqo

#H#

#H)T!!

[ ][ ][ ]

+=2

1

)(2)(32

)(42!n

gaq

aqo

##H

#H)T!!

( )K)

CTatmPtota"

=

==

mo!kJ103143.8

151

3

*t #hat Dartial Dressure #ould


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*t #hat Dartial Dressure #ould

(O,eaction !e at =uili7rium?S8&(g)

"&S8

(a6)

m*atm

mo",-!#H#H# oaq"g

0285.0,

0.3)(32)(2)(2 +=+

[ ]

[ ][ ]

+=

)(2)(2

)(32!n

"g

aqo

#H#

#H)T!!

( )K)CTatmPtota"

===

mo!kJ103143.8

1513

0=

[ ][ ])(2

)(32

)(2

e' "

o

aq

g

#H)T

!

#H#

=


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2ill a reaction occur spontaneously5

Change in enthal!y alone will not dictate whether

reaction will !roceed s!ontaneously

oth enthalpyand entropyneed to $econsidered Bi77s free energy %GB&

8nly change in Bi77s free energy %GB& can !redict

whether a reaction will !roceed s!ontaneously

Geactants must hae more energy than !roducts

2hen GB5/ reaction is at e=uili7rium

Forward reaction rate B ac-ward reaction rate

#ill * eaction Droceed?

Can *lso )etermine the =uili7rium Conditions

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225_Module 03 - Chemical Thermodynamics_2015presented-4