termokimia (pertemuan 6)
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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
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!ani+estations o+ Energy
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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
' $hat (e study is the echange o+ energy*et(een the syste# and the surroundings
8urroundings
8yste#
8urroundings
8yste#
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9nits o+ Energy
' joule/: is the a#ount o+ energy needed to#ove a 1;)g #ass a distance o+ 1 #eter1 J = 1 Nm = 1 kgm2/s2
' calorie(calis the a#ount o+ energy needed to
raise the te#perature o+ one gra# o+ (ater 1- :
1 )ilo(att;hour /)$h = .@0 10@:
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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
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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
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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
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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
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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
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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
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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
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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
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Energy Echange
' Energy is echanged *et(een the syste# andsurroundings through either heat echange or
(or) *eing done
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%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
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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
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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
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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
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%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#
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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
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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
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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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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
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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
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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
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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
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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
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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
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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