1 chemical energetics

7/21/2019 1 Chemical Energetics

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CHEMICALENERGETICS

ENERGY CHANGES INCHEMICAL RXNS



In chemical rxns, energy is alwaysgiven ou or a!en in" This energy isusually in he #orm o# HEAT!



Exothermic reactionsEnergy is GIVEN OUT!

Tem$eraure o# he surroun%ings RISES!Conainer #eels hotter

ro"#ctsha$eLO%ERener&'

than thereactants!

Ener (e$e( "ia ram o) exothermic reactions



Energy changes in reacions arecause% &y he &rea!ing ' ma!ingo# chemical &on%s"

*on" Ma+in& ,-Exothermic rocess

*on" *rea+in& ,-En"othermic rocess



*on"sha$e to/e

/ro+en0st1thenne2/on"s



Acivaion Energy

In or%er o &rea! he &on%s, hereacan $aricles mus colli%e wiheach oher" However, hese collisionsmus ha$$en wih

s#3cient ener&'in or"er to /rea+ the /on"s in hereacans"

The minim#m amo#nt o) ener&'re(uire% o /rea+ the /on"s in thereactant 4or start the reaction5 is

calle% )acti$ation ener&'"*



Exam$les o# exohermic

reacions+Ne#tra(i6ation 4aci"7/ase5reactions

Com/#stion reactions 4/#rnin&

)#e(s (i+e nat#ra( &as1 ethano(1an" h'"ro&en5

Res8iration

Meta(9aci" rxns



En"othermic reactionsEnergy is TA:EN IN!

Tem$eraure o# he surroun%ings GOES;O%N! Conainer #eels co("

ro"#cts ha$eHIGHERener&'than

thereactants!

Ener (e$e( "ia ram o) en"othermic reactions



Exam$les o# en%ohermic

reacions+hotos'nthesisReactions ha88enin& in coo+in&



<=>?+@

ener&'

isre(ease

"

BB +@ener&'

is&aine"



ENERGY ROM UELS



uel-

Any su&sance we use o $rovi%eenergy"

The &urning o# #uels is en"othermic D

exothermic"



The #ossil #uels-

Coal, $eroleum .oil/, naural gas.mehane/



Two #uels growing inim$orance-

Ethano( 4ma"e )rom s#&ar canean" corn7777mixe" 2ith 8etro( or#se" in car en&ines5

H'"ro&en 4#se" in )#e( ce((s5



E(uaions o# he #uels #or&urning-

CH4& 5 9

CHBOH 4(5 9

H 4&5 9

0hich o# hese



N#c(ear )#e(sF%o no &urn"

Have #nsta/(era"ioisoto8es" These&rea! %own naurallyino new aoms,

$ro%ucing a (ot o)energy"

No CO or air

8o((#tants release%"in%ing a sa#e $lace#or he ra"ioacti$e2aste an% ris! o#ex (osions



SIMLE CELLS TORO;UCE ENERGY4ELECTRICITY5



Ho2 to ma+e a sim8(ece((

T2o "ierentmeta(s4e(ectro"es5 are"i88e" into ane(ectro('te an"connecte"externa((' 2ith

a con"#cti$e2ire

E(ectricit' is F

i i



-n is more acti$emeta( than C#There)ore1 it (oses

e(ectrons an"/ecomes oxi"i6e" n 4s5 n94aJ5 9e7

-E(ectrons Ko2 a(on&the 2ire to the C#stri81 as a c#rrent

-H9 ions in thee(ectro('te &ain thee(ectrons on the C#stri an" )orm

So

-E(ectricit' is 8ro"#ce"as a res#(ts o) constantmotion o) e(ectrons inthe externa( circ#it42ire5

-A re"ox rxn is

A t ,

8 o ( e 1

e 7 a r e

L O S

T !



l



Exam$le05 ;ra2 the "ia&ram o) a ce(()orme" 2ith M& an" Si($er meta(s

"i88e" into aJ#eo#s so(#tion o)A&NO?

5 I"enti)' the s#/stances oxi"i6e"

an" re"#ce"



1i2erences &eweenelecrolysis an% volaic cells+

3/

4/

THE HY;ROGEN UEL



THE HY;ROGEN UELCELL

- E(ectro"es are C 7 Not r#nnin&o#t o) H

On( 2ater is )orme" 4no o((#tants5!

H

is

$er'Kamma/(e! Ris+

o)ex8(osionF

1 chemical energetics

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