Termokimia (pertemuan 6)

7/23/2019 Termokimia (pertemuan 6)

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Copyright 2011 Pearson Education, Inc.

Chapter 6Thermochemistry

Chemistry: A Molecular Approach, 2nd Ed.

Nivaldo Tro

Roy ennedy

!assachusetts "ay Co##unity College

$ellesley %ills, !&


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Che#ical %and $ar#ers

' !ost hand (ar#ers (or) *y using the heatreleased +ro# the slo( oidation o+ iron

- e/s 32/g 4 2 e23/s

' The a#ount your hand te#perature risesdepends on several +actors

the si5e o+ the hand (ar#er

the si5e o+ your glove, etc.

#ainly, the a#ount o+ heat released *y the

reaction

2Tro6 Che#istry6 & !olecular &pproach, 27e


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!ani+estations o+ Energy

Tro6 Che#istry6 & !olecular &pproach, 27e


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8yste# and 8urroundings

' $e de+ine the systemas the #aterial or process(ithin (hich (e are studying the energy changes(ithin

' $e de+ine the surroundingsas everything else(ith (hich the syste# can echange energy (ith

' $hat (e study is the echange o+ energy*et(een the syste# and the surroundings

8urroundings

8yste#

8urroundings

8yste#

-Tro6 Che#istry6 & !olecular &pproach, 27e


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9nits o+ Energy

' joule/: is the a#ount o+ energy needed to#ove a 1;)g #ass a distance o+ 1 #eter1 J = 1 Nm = 1 kgm2/s2

' calorie(calis the a#ount o+ energy needed to

raise the te#perature o+ one gra# o+ (ater 1- :

1 )ilo(att;hour /)$h = .@0 10@:

ATro6 Che#istry6 & !olecular &pproach, 27e


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The irst Ba( o+ Ther#odyna#ics

Ba( o+ Conservation o+ Energy

' Thermodynamicsis the study o+ energy and its interconversions

' The irst Ba( o+ Ther#odyna#ics is the Ba( o+ Conservation o+Energy

' This #eans that the total a#ount o+ energy in the universe isconstant

' ou can there+ore never design a syste# that (ill continue toproduce energy (ithout so#e source o+ energy

@Tro6 Che#istry6 & !olecular &pproach, 27e


7/39Copyright 2011 Pearson Education, Inc.

Energy lo( and

Conservation o+ Energy

' Conservation o+ energy reDuires that the su# o+ theenergy changes in the syste# and the surroundings

#ust *e 5ero

Energyuniverse

= 0 = Energysyste#

Energysurroundings

Is the sy#*ol that is

used to #ean change +inal a#ount initial a#ount

FTro6 Che#istry6 & !olecular &pproach, 27e



Internal Energy

' The internal energyis the su# o+ the )inetic andpotential energies o+ all o+ the particles that co#pose

the syste#

' The change in the internal energy o+ a syste# only

depends on the a#ount o+ energy in the syste# atthe *eginning and end

a state !unctionis a #athe#atical +unction (hose result

only depends on the initial and +inal conditions, not on the

process usedE = E+inal Einitial

Ereaction= EproductsG Ereactants

>Tro6 Che#istry6 & !olecular &pproach, 27e



Energy Hiagra#s

' Energy diagra#s are a

JgraphicalK (ay o+ sho(ingthe direction o+ energy +lo(during a process

InternalEne

rgy

initial

+inalenergy added

E =

InternalEnergy

initial

+inal

energy re#oved

E = L

' I+ the +inal condition has a

larger a#ount o+ internal energy than the initialcondition, the change in the

internal energy (ill *e

' I+ the +inal condition has as#aller a#ount o+ internal

energy than the initialcondition, the change in the

internal energy (ill *e L




Energy lo(

' $hen energy +lo(s out o+ asyste#, it #ust all +lo( intothe surroundings

' $hen energy +lo(s out o+ asyste#, Esyste#is L

' $hen energy +lo(s into thesurroundings, Esurroundingsis

' There+ore6

LEsyste#= Esurroundings

8urroundings

E

8yste#

E L




Energy lo(

' $hen energy +lo(s into asyste#, it #ust all co#e+ro# the surroundings

' $hen energy +lo(s into asyste#, Esyste#is

' $hen energy +lo(s outo+ the surroundings,

Esurroundingsis L

' There+ore6

Esyste#= L Esurroundings

8urroundings

E L

8yste#

E




energy

released

Ern= L

energy

a*sor*ed

Ern=

Energy lo( in a Che#ical Reaction' The total a#ount o+ internal energy in 1#ol

o+ C/s and 1 #ole o+ 32/g is greater thanthe internal energy in 1 #ole o+ C32/g

at the sa#e te#perature and pressure

' In the reaction C/s 32/g 4 C32/g, there(ill *e a net release o+ energy into the

surroundings GEreaction= Esurroundings

' In the reaction C32/g 4 C/s 32/g, there(ill *e an a*sorption o+ energy +ro# the

surroundings into the reaction

Ereaction= G Esurroundings

Inte

rnalEnergy

C32/g

C/s, 32/g

8urroundings

8yste#

C 324 C32

8yste#

C32 4C 32




Energy Echange' Energy is echanged *et(een the syste# and

surroundings through heatand (or)q= heat /ther#al energyw= (or) energyqand ware N3T state +unctions, their value depends

on the processE= q+ w




Energy Echange

' Energy is echanged *et(een the syste# andsurroundings through either heat echange or

(or) *eing done

1-Tro6 Che#istry6 & !olecular &pproach, 27e



%eat, $or), and Internal Energy' In the previous *illiard *all ea#ple, the Eo+ the (hite *all is the sa#e

+or *oth cases, *ut qand ware not

' 3n the rougher ta*le, the heat loss, q, is greater qis a #ore negative nu#*er

' "ut on the rougher ta*le, less )inetic energy is trans+erred to the purple*all, so the (or) done *y the (hite *all, w, is lesswis a less negative nu#*er

' The Eis a state +unction and depends only on the velocity o+ the (hite*all *e+ore and a+ter the collision in *oth cases it started (ith A.0 ): o+ )inetic energy and ended (ith 0 ): *ecause it

stopped

q wis the sa#e +or *oth ta*les, even though the values o+ qand ware di++erent

1ATro6 Che#istry6 & !olecular &pproach, 27e



Ea#ple @.16 I+ the *urning o+ the +uel in a potato cannon

per+or#s >AA : o+ (or) on the potato and

produces 1-22 : o+ heat, (hat is E+or the *urning o+ the +uelM

the unit is correct, the sign #a)e sense as the +uel

should lose energy during the reaction

qpotato= >AA :, wpotato= 1-22 :

E+uel,:

Check"

#olution"

Concept $lan"

%elationships"

&i'en"

ind"

qsyste#= Gqsurroundings, wsyste#= Gwsurroundings, E = q + w

1@Tro6 Che#istry6 & !olecular &pproach, 27e



Practice Reacting A0 #B o+ %2/g (ith A0 #B o+ C2%-/g

produces A0 #B o+ C2%@/g at 1.A at#. I+ the reaction

produces .1 102: o+ heat and the decrease in volu#e

reDuires the surroundings do F.@ : o+ (or) on the gases, (hat

is the change in internal energy o+ the gasesM

1FTro6 Che#istry6 & !olecular &pproach, 27e



I+ the reaction produces .1 102: o+ heat and the decrease in

volu#e reDuires the surroundings do F.@ : o+ (or) on the

gases, (hat is the change in internal energy o+ the gasesM

the units are correct, the sign is reasona*le as the a#ount o+ heat lost in the

reaction is #uch larger than the a#ount o+ (or) energy gained

qreaction= G10 :, (surroundings= GF.@ :

Egases,:

Check"

#olution"

Concept $lan"

%elationships"

&i'en"

ind"

qsyste#= Gqsurroundings, wsyste#= Gwsurroundings, E = q + w

1>Tro6 Che#istry6 & !olecular &pproach, 27e



%eat Echange

' )eatis the exchangeo+ ther#al energy *et(een thesyste# and surroundings

' %eat echange occurs (hen syste# and surroundingshave a di++erence in te#perature

' Temperatureis the measureo+ the a#ount o+ ther#alenergy (ithin a sa#ple o+ #atter

' %eat +lo(s +ro# #atter (ith high te#perature to #atter(ith lo( te#perature until *oth o*?ects reach the sa#e

te#perature

ther#al eDuili*riu#




uantity o+ %eat Energy &*sor*ed6

%eat Capacity

' $hen a syste# a*sor*s heat, its te#peratureincreases

' The increase in te#perature is directlyproportional to the a#ount o+ heat a*sor*ed

' The proportionality constant is called the heatcapacity* Cunits o+ C are :7



actors &++ecting %eat Capacity

' The heat capacity o+ an o*?ect depends on itsa#ount o+ #atter

usually #easured *y its #ass

200 g o+ (ater reDuires t(ice as #uch heat to raise itste#perature *y 1


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8peci+ic %eat Capacity

' !easure o+ a su*stanceOs intrinsic

a*ility to a*sor* heat

' The speci!ic heat capacityis thea#ount o+ heat energy reDuired to

raise the te#perature o+ one gra#o+ a su*stance 1


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uanti+ying %eat Energy

' The heat capacity o+ an o*?ect is proportional toits #ass and the speci+ic heat o+ the #aterial

' 8o (e can calculate the Duantity o+ heata*sor*ed *y an o*?ect i+ (e )no( the #ass,the speci+ic heat, and the te#perature change

o+ the o*?ect

Heat= (mass + (speci!ic heat + (temp, change

q= (m + (Cs + (T



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Ea#ple @.26 %o( #uch heat is a*sor*ed *y a copper

penny (ith #ass .10 g (hose te#perature rises +ro#

G>.0


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Practice Calculate the a#ount o+ heat released

(hen F.-0 g o+ (ater cools +ro# -< to 2 :7gQC

2ATro6 Che#istry6 & !olecular &pproach, 27e


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Practice Calculate the a#ount o+ heat released

(hen F.-0 g o+ (ater cools +ro# -< to 2 :7gC /Ta*le @.-

T1= -


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D = # Cs T

Cs, &l= 0.0 :7g'QC, Cs, %23= -.1> :7g'QC/Ta*le @.-

Ea#ple @.6 & 2.A;g cu*e o+ alu#inu# initially at -A.>


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Practice & hot piece o+ #etal (eighing

A0.0 g is heated to 100.0


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Copyright 2011 Pearson Education, Inc.2

Practice Calculate the speci+ic heat and

identi+y the #etal +ro# the data

q= # Cs T q#etal= Gq%23

the units are correct, the nu#*er indicates the

#etal is copper

#etal6 A0.0 g, T1= 100.0


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Pressure Solu#e $or)' PS (or) is (or) caused *y a volu#e change against

an eternal pressure' $hen gases epand, S is , *ut the syste# is doing

(or) on the surroundings, so wgasis L

' &s long as the eternal pressure is )ept constant

Workgas= -+ternal $ressure + Change in .olumegas

w= $. to convert the units to ?oules use 101. : = 1 at#B


Ea#ple @ -6 I+ a *alloon is in+lated +ro# 0 100 B to


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Ea#ple @.-6 I+ a *alloon is in+lated +ro# 0.100 B to

1.>A B against an eternal pressure o+ 1.00 at#,

ho( #uch (or) is doneM

the unit is correct the sign is reasona*le *ecause (hen a gas

epands it does (or) on the surroundings and loses energy

S1 = 0.100 B, S2 = 1.>A B, P = 1.00 at#

w,:

Check"

#olution"

Conceptual

$lan"

%elationships"

&i'en"

ind"

101. : = 1 at#B


Practice & certain process results in a gas syste# releasing


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Practice & certain process results in a gas syste# releasing

@>. ): o+ energy. Huring the process, 1A.> )cal o+ heat is

released *y the syste#. I+ the eternal pressure is )ept

constant at 1.00 at# and the initial volu#e o+ the gas is 10.0 B,

(hat is the +inal volu#e o+ the gasM/1 cal = -.1> :, 101. : = 1.00 at#'B


Practice & certain process results in a gas syste# releasing @> ): o+


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Practice & certain process results in a gas syste# releasing @>. ): o+

energy. Huring the process, 1A.> )cal o+ heat is released *y the syste#.

I+ the eternal pressure is )ept constant at 1.00 at# and the initial volu#e

o+ the gas is 10.0 B, (hat is the +inal volu#e o+ the gasM

so *oth E and qare G, and E q,w#ust *e G and (hen w

is G the syste# is epanding, so S2should *e greater than S1

and it is

E= G@>. ):, q= G1A.> )cal, S1 = 10.0 B, P = 1.00 at#

S2, B

Check"

#olution"

Conceptual

$lan"

%elationships"

&i'en"

ind"

E= q w, w= GPS, 1 ): = 1000 :, 1 cal = -.1> :, 101. : = 1 at#B

q, E w

S2P, S1

E= G@.> 10-

:, q= G@.@0- 10-

:, S1 = 10.0B, P = 1.00 at#

S2, B



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Echanging Energy "et(een

8yste# and 8urroundings

' Echange o+ heat energy

q = #ass speci+ic heat Te#perature

' Echange o+ (or)w= GPressure Solu#e

-Tro6 Che#istry6 & !olecular &pproach, 27e


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!easuring E,

Calori#etry at Constant Solu#e' "ecause E = q + w, (e can deter#ine E*y #easuring qand

w

' In practice, it is easiest to do a process in such a (ay that thereis no change in volu#e, so w= 0

at constant volu#e, Esyste#= qsyste#' In practice, it is not possi*le to o*serve the te#perature changes

o+ the individual che#icals involved in a reaction so instead, (e#easure the te#perature change in the surroundings use insulated, controlled surroundings

qsyste#= Gqsurroundings

' The surroundings is called a 0om0 calorimeterand is usually#ade o+ a sealed, insulated container +illed (ith (ater

qsurroundings= qcalorimeter= qsystem

ATro6 Che#istry6 & !olecular &pproach, 27e


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"o#* Calori#eter

' 9sed to #easure E

*ecause it is a constantvolu#e syste#

' The heat capacity o+ thecalori#eter is the a#ount

o+ heat a*sor*ed *y the

calori#eter +or each

degree rise in

te#perature and is called

the calorimeter constant

Ccal, ):7QC

@Tro6 Che#istry6 & !olecular &pproach, 27e

Ea#ple @ A6 $hen 1 010 g o+ sugar is *urned in a *o#*


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Ea#ple @.A6 $hen 1.010 g o+ sugar is *urned in a *o#*

calori#eter, the te#perature rises +ro# 2-.2 .


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Practice $hen 1.22 g o+ %CF%A32/!! 122.12 is *urned in

a *o#* calori#eter, the te#perature rises +ro# 20.2F


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g F A 2calori#eter, the te#perature rises +ro# 20.2F

Termokimia (pertemuan 6)

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