ki1101-2012-kd lec06a energyandchemicalchanges thermochemistry

8/10/2019 KI1101-2012-KD Lec06a EnergyAndChemicalChanges ThermoChemistry

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Prentice-Hall 2007General Chemistry: Chapter 7Slide 1 of 58

Philip !tton"ni#ersity of $indsor% Canada

Prentice-Hall 2007

CH&'(S)*+

NinthEdition G&,&* .

Principles and 'odern pplications

Petrucci Harwood Herring Madura

Chapter 7: )hermochemistry


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Prentice-Hall 2007General Chemistry: Chapter 7Slide / of 58

Gettin Started: Some )erminolo y

)hermochemistry is the st!dy of heat chan e inchemical reactionsSystem the reactions or area !nder st!dy

S!rro!ndin s the restof the !ni#erse o!ndaries3$all a 4order 4et een thesystem and s!rro!ndin s


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pen Closed (solated Systems

pen Systems can ainor lose mass3matter andener y across their

4o!ndaries

i e h!man 4ody

Closed Systems cana4sord or release ener y 4!t not mass3matter%across the 4o!ndary

i e li ht 4!l4

(solated Systems9adia4atic cannot

e;chan e matter or ener yith their s!rro!ndin si e closed )hermos ottle


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)erminolo y

&ner y% ")he capacity to do or< 9mo#e mass o#er a distanceor transfer of heat

)ypes of ener y :


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&ner y can 4e transferred 4y mo#in particlesCollosion of fast particles ith slo er particlesca!ses the slo particles to speed !p hile the

fast molec!ls slo s)his is hy hot aters cools in contact ithcool air

=inetic &ner y is the ener y of motions


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Potential &ner y&ner y d!e to condition% position% or composition

ssociated ith forces of attraction or rep!lsion

4et een o4Dects&ner y can chan e from potential to


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Prentice-Hall 2007General Chemistry: Chapter 7Slide E of 58

Potential &ner y epends on Position

Potential ener y increase hen4Dect that attract mo#e apart% or 4Dect that repel mo#e to ards each others

Stored ener y that can 4e con#erted to


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Potential and =inetic &ner y

Slide 7 of 58 General Chemistry: Chapter 7 Prentice-Hall 2007


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&ner y and )emperat!re

)hermal &ner y=inetic ener y associated ith randommolec!lar motion

(n eneral proportional to temperat!ren intensi#e property

Heat and $or<

F and &ner y chan es


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$hat is )emperat!re

)emperat!re 9) is proportional to the a#era e


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Prentice-Hall 2007General Chemistry: Chapter 7Slide 1/ of 58

"nits of &ner y

S( !nit is the Bo!le% BB ? < Jm23s2(f the calc!lated #al!e is reater than 1000 B% !se the


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Conser#ation of &ner y

&ner y cannot 4e created or destroyed% 4!t can 4etransformed from one form of ener y to anotherlso


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Heat

lso called )H&*' . &,&*G+&ner y transferred 4et een a system and itss!rro!ndin s as a res!lt of a temperat!redifferenceHeat flo s from hotter to colder !ntil theyreach thermal eF!ili4ri!m

)emperat!re may chan ePhase may chan e 9an isothermal process

metal spoon at 25 C is placed in 4oilinater $hat happens


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Prentice-Hall 2007General Chemistry: Chapter 7Slide 1> of 58

Heat of *eaction

&;othermic reactions is any process that i#es off heat transfer thermal ener y from system to the s!rro!ndin s&ndothermic reactions is any process in hich heat has to

4e s!pplied to the system for the s!rro!ndin s


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&;othermic reactionsProd!ces heat% F r;n L 0

&ndothermic reactionsCons!mes heat% F r;n M 0

Calorimeter de#ice for meas!rin

F!antities of heat

Heats of *eaction

ddater


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Heats of *eaction and Calorimetry

Chemical ener yContri4!tes to the internal ener y of a system

Heat of reaction% Fr;n)he F!antity of heat e;chan ed 4et een asystem and its s!rro!ndin s hen a chemicalreaction occ!rs ithin the system% at constant

temperature.


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Prentice-Hall 2007General Chemistry: Chapter 7Slide 1E of 58

Heat Capacity

)he F!antity of heat reF!ired to chan e thetemperat!re of a system 4y one de ree

'olar heat capacityNSystem is one mole of s!4stance

Specific heat capacity% cNSystem is one ram of s!4stance

Heat capacityN'ass specific heat

F ? mc )

F ? C )


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Specific Heat and Heat Capacity

)he specific heat 9s of a s!4stance is theamo!nt of heat 9F reF!ired to raise thetemperat!re of one ram of the s!4stance

4y one de ree Celsi!s

)he heat capacity 9C of a s!4stance is theamo!nt of heat 9F reF!ired to raise thetemperat!re of a i#en F!antity 9m of thes!4stance 4y one de ree Celsi!s

C ? m sF ? m s O)F ? C O)


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etermination of Specific Heat


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Determinin Specific Heat from !"perimental Data# "se thedata presented on the last slide to calc!late the specific heat oflead

Flead ? -F ater

F ater ? mc ) ? 950 0 96 186 B3 C 928 8 - 22 0 C

F ater ? 1 6 10 / B

Flead ? -1 6 10/

B? mc ) ? 9150 0 9clead 928 8 - 100 0 C

clead ? 0 1/ B -1 C-1

EXAMPLE 7-2


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om4 Calorimeter 9Constant ol!me Calorimetry

q sys = q water + q bomb + q rxnq sys = 0

q rxn = - ( qwater + q bomb )

qwater = m x s x t q bomb = C bomb x t

eaction at !onstant V

H " q rxnH = q rxn


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$sin %om& Calorimetry Data to Determine a Heat of'eaction# )he com4!stion of 1 010 s!crose% in a 4om4calorimeter% ca!ses the temperat!re to rise from 26 E2 to28 // C )he heat capacity of the calorimeter assem4ly is 6 E0


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Calculate q calorimeter :

Fcal ? C ) ? 96 E0


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Calculate q rxn in the required units:Fr;n ? -F cal ?

-1> 7 5 5 5 10 / 5


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Coffee C!p Calorimeter 9Constant Press!re Calorimetry

simple calorimeter $ell ins!lated and therefore isolated 'eas!re temperat!re chan e

Fr;n ? -F cal

See e;ample 7-6 for a sample calc!lation


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Coffee C!p Calorimeter 9Constant Press!re Calorimetry

q sys = qwater + q ca# + q rxnq sys = 0

q rxn = - ( q water + q ca#)qwater = m x s x t

q ca# = C cal x t

eaction at !onstant P H = q rxn


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Prentice-Hall 2007General Chemistry: Chapter 7Slide /0 of 58

$or<

(n addition to heat effects chemical reactionsmay also do work.

Gas formed p!shes a ainstthe atmosphere

ol!me chan es

Pressure volume work.


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Press!re ol!me $or<

? d

? 9m

9m

? P

? P e;t

h?

h


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$or< and PistonsQ Press!re ? force3areaQ (f the container

#ol!me chan es% the press!re chan es

Q $or< ? - P R O! "nits: . Q atm1 . Q atm ? 101 B

Q (n e;pansion% O ! M 0%and is e;othermic

Q $or< is done "y thesystem in e;pansion


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Prentice-Hall 2007General Chemistry: Chapter 7Slide // of 58

Ho does or< relate to reactions

Q $or< ? orce istanceQ (s most often d!e to the e;pansion or contraction of

a system d!e to chan in moles of asQ Gases p!sh a ainst the atmospheric press!re % so P system ? - P atm

w ? - P atm R O!

Q )he deployment of an air4a is one e;ample of this process

1C / H89 g K5 29 g T / C 29 g K6H2 9 g

> moles of as T 7 moles of as


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#ssume an ideal gas and calculate the volume change:

Calc(latin Press(re-)ol(me *or+# S!ppose the as in the

cham4er is 0 100 mol He at 2E8 = and an e;ternal press!re of1 20 atm Ho m!ch or


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Calculate the work done "y the system:

? P

? 91 20 atm 91 02 . 9

? 1 26 10 2 B

-101 B1 . atm

$here did the conversion factor come from%

Compare t o #ersions of the as constant and calc!late

8 /165 B3mol = U 0 082057 . atm3mol =

1 U 101 // B3. atm

&int: 'f you use pressure in kPa you get (oules directly.

# negative value signifies that work is done )* the surroundings

EXAMPLE 7-5


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Prentice-Hall 2007General Chemistry: Chapter 7Slide /> of 58

&ner y can 4e )ransferred as Heat and $or<

Q O+ ? q K wQ (nternal ener y

chan es arestate f!nctions


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7-5 )he irst .a of )hermodynamics

(nternal &ner y%")otal ener y 9potential and


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irst .a of )hermodynamics

system contains only internal ener y system does not contain heat or or Heats of *eaction: " and H

*eactants T Prod!cts" i " f

" ? " f - " i

? F r;n K

'n a system at constant volume:

" ? Fr;n

K 0 ? Fr;n

? F#

!t e li#e in a constant press!re orldV

Ho does F p relate to F #


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Heats of *eaction


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Heats of *eactionF ? F P K

$e


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Comparin Heats of *eaction

FP ? -5>>


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Chan es of State of 'atter

H2 9l T H 2 9 H ? 66 0 01


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reak the pro"lem into two steps: *aise the temperat!re ofthe liF!id first then completely #aporiWe it )he total enthalpychan e is the s!m of the chan es in each step

!nthalpy Chan es ,ccompanyin Chan es in States of

atter# Calc!late H for the process in hich 50 0 of ateris con#erted from liF!id at 10 0 C to #apor at 25 0 C

? 950 0 96 186 B3 C 925 0-10 0 C K50 0 18 0 3mol

66 0


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Standard States and Standard &nthalpyChan es

efine a partic!lar state as a standard stateStandard enthalpy of reaction% H

)he enthalpy chan e of a reaction in hich allreactants and prod!cts are in their standard states

Standard State

)he p!re element or compo!nd at a press!re of1 4ar and at the temperat!re of interest


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&nthalpy ia rams


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&nthalpy ia rams


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7-7 (ndirect etermination of H:HessXs .a

H is an e;tensi#e property&nthalpy chan e is directly proportional to the amo!nt ofs!4stance in a system

, 29 K 29 T 2 , 9 H ? K180 50


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HessXs .a

HessXs la of constant heat s!mmation(f a process occ!rs in sta es or steps 9e#en hypothetically %the enthalpy chan e for the o#erall process is the s!m of theenthalpy chan es for the indi#id!al steps

I, 29 K 29 T , 29 H ? K// 18


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HessXs .a Schematically


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*!les for ddin )hermochemical *;

1 $hen an eF!ation is re#ersedY ritten in theopposite directionYthe si n of & m!st also 4ere#ersed

2 orm!las canceled from 4oth sides of aneF!ation m!st 4e for the s!4stance in identical

physical states/ (f all the coefficients of an eF!ation are

m!ltiplied or di#ided 4y the same factor% the#al!e of & m!st li


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Strate y for ddin *eactions )o ether

1 Choose the most comple; compo!nd in theeF!ation 91

2 Choose the eF!ation 92 or / orZ that containsthe compo!nd

/ $rite this eF!ation do n so that the compo!ndis on the appropriate side of the eF!ation and hasan appropriate coefficient for o!r reaction

6 .oo< for the ne;t most comple; compo!nd


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Hess[s .a 9Cont

1 Choose an eF!ation that allo s yo! to cancelintermediates and m!ltiply 4y an appropriatecoefficient

2 dd the reactions to ether and cancel li


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>0

Ho can e calc!late the enthalpy chan e for thereaction 2 H 29 g K , 29 g T , 2H69 g ! sin theseeF!ations

, 2H69 g K H29 g T 2,H / 9 g O & ? -187 8


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Prentice-Hall 2007General Chemistry: Chapter 7Slide >1 of 58

)he enthalpy chan e that occ!rs in theformation of one mole of a s!4stance in the

standard state from the reference forms ofthe elements in their standard states

)he standard enthalpy of formation of a p!re element in its reference state is 0

H f

7-8 Standard &nthalpies of ormation


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Standard States


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Prentice-Hall 2007General Chemistry: Chapter 7Slide >/ of 58

Standard &nthalpy of ormation


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Standard &nthalpies of ormation


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Standard &nthalpies of *eaction

H o#erall ? -2 H f ,aHC / K H f ,a 2C /

K

H f C 2 K H f H2


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Prentice-Hall 2007General Chemistry: Chapter 7Slide >> of 58

&nthalpy of *eaction

H r;n ? H f prod!cts - H f reactants

)a4le 7 / &nthalpies of ormation of (ons


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)a4le 7 / &nthalpies of ormation of (onsin F!eo!s Sol!tions


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7-E !els as So!rcesof &ner y

ossil f!elsCom4!stion is e;othermic

,on-rene a4le reso!rce&n#ironmental impact

$ ld P i & C ! i


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Prentice-Hall 2007General Chemistry: Chapter 7Slide >E of 58

$orld Primary &ner y Cons!mption

p e t r o l e !

m

c o a l

n a t ! r a l 0 a s 5 i nd

n!clear

G h ! &ff


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Greenho!se &ffect

C i th t h


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C 2 in the tmosphere

G l o 4 a l -

# e r a 0 e

t! l d P di t d & i i f C


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ct!al and Predicted &mission of C 2

p e t r o l e ! m

c o a l n a t ! r a l 0 a

s

t o t a l

! C 4 h d d


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oc!s on: ats Car4ohydrates and&ner y Stora e

& l! f t d C 4 h d t


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&ner y al!es of ats and Car4ohydrates

1 cal ? 6 186 B

& d f Ch t \! ti


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See< help ith pro4lems!t only after str! lin ith them)he initial effort pays off

"nderstandin occ!rs hen sol!tions aree;plained 4y peers% t!tors or professors

o not o strai ht to the sol!tion man!al+o! only think that yo! !nderstand the sol!tion

if yo! ha#e not or

ki1101-2012-kd lec06a energyandchemicalchanges thermochemistry

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