VI. Thermochem Dinamic

8/9/2019 VI. Thermochem Dinamic

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1Chapter VI:Chapter VI:THERMOCHEMISTRYTHERMOCHEMISTRY

ThermodynamicsThermodynamicsThe study of Heat and WorkThe study of Heat and Work

and State unctionsand State unctions


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Ener!y " ChemistryEner!y " Chemistry


ENERGYENERGYis the capacity tois the capacity todo work or transfer heat.do work or transfer heat.

HEATHEATis the form of energyis the form of energythat flows etween 2 o!ectsthat flows etween 2 o!ects

eca"se of their difference ineca"se of their difference intemperat"re.temperat"re.

#ther forms of energy $#ther forms of energy $

lightlight

electricalelectrical

kinetic and potentialkinetic and potential


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%


&"rning pean"ts s"pply s"fficient energypean"ts s"pply s"fficient energyto oil a c"p of water.to oil a c"p of water. &"rning s"gar&"rning s"gar

's"gar reacts with's"gar reacts with

()l#()l#%%* a strong* a strongo+idi,ing agent-o+idi,ing agent-
http://xbeams.chem.yale.edu/~batista/113/movies/06z01vd1.mov


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These reactions areThese reactions are /R#0)T A3#RE0/R#0)T A3#RE0

They proceed almost completely fromThey proceed almost completely from

reactants to prod"cts* perhaps withreactants to prod"cts* perhaps withsome o"tside assistance.some o"tside assistance.


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2 H2 H22'g- 5 #'g- 5 #22'g- 667'g- 6672 H2 H22#'g- 5 heat and light#'g- 5 heat and light

This can e set "p to pro8ideThis can e set "p to pro8ide

E9E)TR:) ENERGYE9E)TR:) ENERGYin ain a fue#fue#

ce##ce##..#+idation;#+idation;

2 H2 H226667 H6667 H55 5 e5 e66

Red"ction;Red"ction;

e e66 5 #5 #22 5 2 H5 2 H22# 6667 #H# 6667 #H66

))R* page


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$otentia# " %inetic Ener!y$otentia# " %inetic Ener!y$otentia# " %inetic Ener!y$otentia# " %inetic Ener!y

Potential energyPotential energy energy a energy amotionlessmotionless

body has bybody has byvirtue of itsvirtue of itsposition.position.


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/ositi8e andnegati8e particles'ions- attract oneanother.

Two atoms canond

As the particlesattract they ha8e a

lower potentialenergy

$otentia# Ener!y$otentia# Ener!yon the &tomic Sca#eon the &tomic Sca#e

Na)l $ composed ofNa)l $ composed of

NaNa55and )land )l66ions.ions.


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Kinetic energyKinetic energy energy of energy ofmotionmotion

TranslationTranslation


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Kinetic energyKinetic energyenergy ofenergy ofmotion.motion.

translate

rotate

vibratetranslate

rotate

vibrate


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Interna# Ener!y 'E(Interna# Ener!y 'E(

/E 5 (E :nternal energy 'E or -/E 5 (E :nternal energy 'E or -

:nt. E of a chemical system:nt. E of a chemical system

depends ondepends on n"mer of particlesn"mer of particles

type of particlestype of particles

temperat"retemperat"re


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/E 5 (E :nternal energy 'E or -/E 5 (E :nternal energy 'E or -

QuickTime and aGraphics decompressor

are needed to see this picture.


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The higher the TThe higher the T

the higher thethe higher the

internal energyinternal energy Bo* "se changesBo* "se changes

in T 'CT- toin T 'CT- to

monitor changesmonitor changes

in E 'CE-.in E 'CE-.


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+irectiona#ity of Heat Transfer+irectiona#ity of Heat Transfer

Heat always transfer from hotter o!ect to

cooler one.

E,Othermic; heat transfers from SYSTEMtoS-RRO-.+I./S.

T'system- goes downT'system- goes down

T's"rr- goes "pT's"rr- goes "p


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+irectiona#ity of Heat Transfer+irectiona#ity of Heat Transfer

Heat always transfer from hotter o!ect to

cooler one.

E.+Othermic; heat transfers fromS-RRO-.+I./S to theSYSTEM.

T'system- goes "pT'system- goes "p

T 's"rr- goes downT 's"rr- goes down


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All of thermodynamics dependsAll of thermodynamics dependson the law ofon the law of

CO.SERV&TIO. O E.ER/YCO.SERV&TIO. O E.ER/Y00

The total energy is "nchanged inThe total energy is "nchanged ina chemical reaction.a chemical reaction.

:f /E of prod"cts is less than:f /E of prod"cts is less than

reactants* the difference m"st ereactants* the difference m"st ereleased as (E.released as (E.


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1 H(g) ---> H22O(g) + 242 kJO(g) + 242 kJ

HH22O(g) ---> HO(g) ---> H22O(liq) + 44 kJO(liq) + 44 kJ

-----------------------------------------------------------------------

HH22(g) + 1/2 O(g) + 1/2 O22(g) --> H(g) --> H22O(liq) + 286 kJO(liq) + 286 kJ

Example ofExample ofHESSS 8&WHESSS 8&W

If a r;n0 is the sum of < or moreIf a r;n0 is the sum of < or moreothers6 the net 2H is the sum of theothers6 the net 2H is the sum of the2Hs of the other r;ns02Hs of the other r;ns0

-SI./ E.TH&8$Y-SI./ E.TH&8$Y

Hesss 8a3Hesss 8a3


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Hess s 8a3Hess s 8a3" Ener!y 8e5e# +ia!rams" Ener!y 8e5e# +ia!rams

orming H2# can occ"r in a

single step or in a twosteps.

CHtotalis the same no matter

which path is followed.

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Hesss 8a3Hesss 8a3


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Hess s 8a3Hess s 8a3" Ener!y 8e5e# +ia!rams" Ener!y 8e5e# +ia!rams

orming )#2can occ"r in asingle step or in a two steps.

CHtotalis the same no matterwhich path is followed.

=

CCH l thH l th


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This eD"ation is 8alid eca"seThis eD"ation is 8alid eca"seCH is aCH is a ST&TE -.CTIO.ST&TE -.CTIO.

These depend only on the stateThese depend only on the state

of the system andof the system and notnoton howon howthe system got there.the system got there.

3* T* /* energy $ and yo"r ank3* T* /* energy $ and yo"r ankacco"ntOacco"ntO

nlike 3* T* and /* one cannotnlike 3* T* and /* one cannotmeas"re asol"te H. )an onlymeas"re asol"te H. )an onlymeas"re CH.meas"re CH.

CCH along one path H along one path

CCH along another pathH along another path

CCH along one path H along one path

CCH along another pathH along another path

>

d d E h # #


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Standard Entha#py Va#uesStandard Entha#py Va#ues

Most H values are labeledMost H values are labeled HHooMeasured underMeasured understandard conditionsstandard conditions

P = 1 bar = 10P = 1 bar = 1055Pa = 1 atm /1.01325Pa = 1 atm /1.01325

Concentration = 1 mol/LConcentration = 1 mol/LT = usually 25T = usually 25ooCC

with all species in standard stateswith all species in standard states

e.g., C = graphite and Oe.g., C = graphite and O22= gas= gas

HO(g) + C(graphite) --> H22(g) + CO(g)(g) + CO(g)

(product is called (product is called water gaswater gas))

42-sin! Standard Entha#py Va#ues-sin! Standard Entha#py Va#ues


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! py! py

HH22O(g) + C(graphite) --> HO(g) + C(graphite) --> H22(g) + CO(g)(g) + CO(g)

From reference books we findFrom reference books we find

HH22(g) + 1/2 O(g) + 1/2 O22(g) --> H(g) --> H22O(g) HO(g) Hff = - 242 kJ/mol = - 242 kJ/mol

C(s) + 1/2 OC(s) + 1/2 O22(g) --> CO(g)(g) --> CO(g) HHff = - 111 kJ/mol = - 111 kJ/mol

4%-sin! Standard Entha#py Va#ues-sin! Standard Entha#py Va#ues


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HH22O(g) --> HO(g) --> H22(g) + 1/2 O(g) + 1/2 O22(g) H(g) H oo= +242 kJ= +242 kJ

C(s) + 1/2 OC(s) + 1/2 O22(g) --> CO(g)(g) --> CO(g) HH oo= -111 kJ= -111 kJ

--------------------------------------------------------------------------------

To convert 1 mol of water to 1 mol each of HTo convert 1 mol of water to 1 mol each of H22

and COand COrequiresrequires131 kJ of energy.131 kJ of energy.

The water gas reaction isThe water gas reaction isENDOENDOthermic.thermic.

HH22O(g) + C(graphite) --> HO(g) + C(graphite) --> H22(g) + CO(g)(g) + CO(g) HHoonetnet= +131 kJ= +131 kJHH22O(g) + C(graphite) --> HO(g) + C(graphite) --> H22(g) + CO(g)(g) + CO(g) HHoonetnet= +131 kJ= +131 kJ

4

- d d E h # V #- i St d d E th # V #


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-sin! Standard Entha#py Va#ues-sin! Standard Entha#py Va#ues

:n general* when:n general* when A99A99

enthalpies of formation areenthalpies of formation areknown;known;

)alc"late CH of)alc"late CH of

reactionKreactionK

HHoorxnrxn== HHffoo

(products) -(products) - HHffoo(reactants)(reactants)HH

oorxnrxn== HHff

oo(products) -(products) - HHff

oo(reactants)(reactants)

Rememer that C always final Q initial

44


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)alc"late the heat of com"stion of)alc"late the heat of com"stion of

methanol* i.e.* CHmethanol* i.e.* CHoor+nr+nforfor

)H)H%%#H'g- 5 %L2 ##H'g- 5 %L2 #22'g- 667 )#'g- 667 )#22'g- 5 2 H'g- 5 2 H22#'g-#'g-CCHHoor+nr+n CHCHffoo'prod- 6'prod- 6 CHCHffoo'react-'react-

4=



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! py! py

CCHHoor+nr+n CH CHffoo')#')#22- 5 2 CH- 5 2 CHffoo'H'H22#-#-

6 %L2 CH6 %L2 CHffoo'#'#22- 5 CH- 5 CHffoo')H')H%%#H-S#H-S

'6%?%.4 k- 5 2 '621.< k- '6%?%.4 k- 5 2 '621.< k-

6 @ 5 '62@1.4 k-S6 @ 5 '62@1.4 k-S

CCHHoor+nr+n 6=>4.= k per mol of methanol 6=>4.= k per mol of methanol

CHCH33OH(g) + 3/2 OOH(g) + 3/2 O22(g) --> CO(g) --> CO22(g) + 2 H(g) + 2 H22O(g)O(g)HHoorxnrxn== HHff

oo(prod) -(prod) - HHff

oo(react)(react)

4>

C&8ORIMETRYC&8ORIMETRY


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Measurin! Heats of Reaction

)onstant 3ol"me&omF )alorimeter

&"rn com"stilesample.

eas"re heat e8ol8edin a reaction.

0eri8e CE forreaction.

4

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