OER Entropy and Free Energy

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The Royal Society of Chemistry 2010-11

Entropy and Free EnergyEntropy and Free Energy

Whatisthisresourceandwhoisitfor?

This is an OpenEducationalResource designed tosummarise keyconcepts in thermodynamics that are

reuired for entry to an undergraduate course! The

resource isdesignedfor1styearundergraduatesand

re"isitsideasfrom#-le"el!$talso%eginstosho&ho&

theyareappliedearlyina'ni"ersitycourse!

$t is therefore anticipated that you &ill ha"e some

kno&ledgeof#-le"elchemistry%eforeundertakingtheacti"ity %ut e"en &ith good su%(ect kno&ledge) there

shouldalso%esomematerialhereyouareunfamiliar

&ith!

This resource isnotdesignedtosupportanyspecific

#-le"elspecification%utmayalso%eused inschools

alongsideotherresources&hereappropriate!

LearningObjectivesOn completion of this acti"ity you

should%ea%leto*

Relateentropytothetemperature

andstateofasu%stanceCalculate S for the system and

surroundings

Calculate G

'se Sor Gtopredict&hethera

process&ill%espontaneous

+escri%e the limitations of S or

G for predicting &hether a

reaction&illoccur

#ppreciate the connection

%et&een entropy and the

distri%ution of energy %et&een

uantised energy le"els in the

system!

RelatedResourcesThis resource %uilds on some of the

ideas presented in the acti"ities on

dynamiceuili%ria!

Whomadeit?+eclan ,leming &orked at the 'ni"ersity of ath as a Teacher

,ello& 2010-2011 as part of The Royal Society of Chemistry.s &ork

under the /ationalESTErogramme! art of his remit &as

lookinginto&aysthate-learningcan%eusedtosupportstudentsat

the3S45Einterface!

+eclan.s &ork is copyright The Royal Society of Chemistry!
https://openeducationalresources.pbworks.com/What-are-Open-Educational-Resourceshttps://openeducationalresources.pbworks.com/What-are-Open-Educational-Resourceshttps://openeducationalresources.pbworks.com/What-are-Open-Educational-Resourceshttp://www.rsc.org/Education/HESTEM/teacherfellows/index.asphttp://www.rsc.org/Education/HESTEM/teacherfellows/index.asphttp://www.rsc.org/Education/HESTEM/teacherfellows/index.asphttp://www.rsc.org/Education/HESTEM/teacherfellows/index.asphttp://www.rsc.org/Education/HESTEM/teacherfellows/index.asphttp://www.rsc.org/Education/HESTEM/teacherfellows/index.asphttp://www.rsc.org/Education/HESTEM/teacherfellows/index.asphttp://www.rsc.org/Education/HESTEM/teacherfellows/index.asphttps://openeducationalresources.pbworks.com/What-are-Open-Educational-Resourceshttps://openeducationalresources.pbworks.com/What-are-Open-Educational-Resourceshttps://openeducationalresources.pbworks.com/What-are-Open-Educational-Resources


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eople and animals can pass out

for many reasons! 6ou can %ereasona%ly certain though that if

you &ere to see it happen) it

&ouldn.t(ust%e%ecauseallof the

o7ygen suddenly found itself on

onesideoftheroom8

Introduction to EntropyIntroduction to Entropy

The reason that some things

seem to happen and others

(ustdon.t)isdo&ntoentropy!

$mage %y9 3it%y

$mage %y9 Rosen
http://www.flickr.com/photos/kitby/http://www.flickr.com/photos/kitby/http://www.flickr.com/photos/rosengrant/http://www.flickr.com/people/10251343@N05http://www.flickr.com/people/10251343@N05http://www.flickr.com/photos/rosengrant/http://www.flickr.com/photos/rosengrant/http://www.flickr.com/photos/rosengrant/http://www.flickr.com/photos/kitby/


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/itrogen and other atmospheric gases

O O

ro%a%ility9 0!4

O O

#

O O

#

#

Introduction to Entropy contd!"Introduction to Entropy contd!"


4/21


/itrogen and other atmospheric gases

O O

ro%a%ility : 0!42: 0!24

O O

# #

# #

O O

O O

O OO O

O O

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Introduction to Entropy contd!"Introduction to Entropy contd!"


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Ludwig &olt'mann

Entropy is a measure of disorder or

randomness! The more &ays you ha"e

of arranging something) the higher its

entropy!

Theunitsofentropy>S?are()*#mol*#

Entropyisdeeplyconnectedtoenergy!

+o what+o what isisEntropy?Entropy?

@Weightof the

configurationA

oltBmann

constant

Entropy is not the reason your %edroomgetsmessy8

Simplistic

definition alert8

$mage %y9 martinroell
http://www.flickr.com/photos/martinroell/427167382/http://www.flickr.com/photos/martinroell/http://www.flickr.com/photos/martinroell/427167382/http://www.flickr.com/people/10251343@N05http://www.flickr.com/photos/martinroell/


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8/21 The Royal Society of Chemistry 2010-11



# spontaneous process) oncestarted &ill continue to&ards

euili%rium&ithoutinter"ention!

In spontaneous processes.entropyincreases*%utho&do

&e account for &ater freezing

spontaneouslyD

$nk mi7ing &ith &ater

happens spontaneously hen ice is remo"edfrom a freeBer) it melts

spontaneously

+pontaneous /rocesses+pontaneous /rocesses

$mage %y9 ikeFtn

$mage %y9 gagstreet
http://www.flickr.com/photos/45818813@N05/4785640636/http://www.flickr.com/photos/45818813@N05/4785640636/http://www.flickr.com/photos/beginasyouare/1182886568/http://www.flickr.com/photos/beginasyouare/1182886568/http://www.flickr.com/photos/beginasyouare/1182886568/http://www.flickr.com/photos/beginasyouare/http://www.flickr.com/photos/45818813@N05/http://www.flickr.com/photos/beginasyouare/1182886568/http://www.flickr.com/photos/45818813@N05/4785640636/http://www.flickr.com/photos/45818813@N05/http://www.flickr.com/photos/beginasyouare/


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$mage %y9Eugen 0os1o

$mage %y9#le7 #nlicker

$mage %y9,heresa )nott

$mage %y9 takkk

$mage %y9

#ndreas Tille

http://commons.wikimedia.org/wiki/Category:Eugen_Noskohttp://de.wikipedia.org/wiki/Benutzer:Alex_Anlickerhttp://en.wikibooks.org/wiki/en:User:Theresa_knotthttp://en.wikibooks.org/wiki/en:User:Theresa_knotthttp://en.wikibooks.org/wiki/en:User:Theresa_knotthttp://en.wikibooks.org/wiki/en:User:Theresa_knotthttp://commons.wikimedia.org/wiki/User:Takkkhttp://commons.wikimedia.org/wiki/User:Tilleahttp://commons.wikimedia.org/wiki/User:Tilleahttp://commons.wikimedia.org/wiki/User:Tilleahttp://commons.wikimedia.org/wiki/User:Tilleahttp://commons.wikimedia.org/wiki/User:Takkkhttp://en.wikibooks.org/wiki/en:User:Theresa_knotthttp://en.wikibooks.org/wiki/en:User:Theresa_knotthttp://en.wikibooks.org/wiki/en:User:Theresa_knotthttp://de.wikipedia.org/wiki/Benutzer:Alex_Anlickerhttp://commons.wikimedia.org/wiki/Category:Eugen_Noskohttp://commons.wikimedia.org/wiki/Category:Eugen_Noskohttp://commons.wikimedia.org/wiki/Category:Eugen_Nosko



e must consider the entropy not only

of the system) %ut of the

surroundings!!

Li2uid

becomes

solid

3eat energy

released to

surroundings

Overall

increase

in

entropy

#s theenergyof thesystemdecreases)

that energy is released to the

surroundings

,he +econd Law of,hermodynamics9

$n a spontaneous process)

the entropy of the Universe

increases!

,he +econd Law of ,hermodynamics,he +econd Law of ,hermodynamics

Ene

rgy

Reaction

Reactants

roducts

Ea

3 4 3eat3 4 3eat

released toreleased to

surroundingssurroundings

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S = Ssys+ Ssurr

,rom data %ook

G22!0 H 3-1

mol-1

Ssurr:

qrev

T

Change in heat

>

fus?

5n e-ample6 Will ice melt at 75n e-ample6 Will ice melt at 7

8?8?

,he entropy of the

9niverse must increase

for a spontaneous

reaction

#%solute Temperature

>3el"in?

Ssurr:->=010 H?

2IJ 3

ill this "alue %e

G"e or K"eD?

S: ;;!$< *;#!=": < $!> ( )*#mol*#

: -21!= H 3-1mol-1

ill this "alue %e

G"e or K"eD?

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13/21

$mage %y9 Today is a Lood +ay

http://www.flickr.com/photos/good_day/http://www.flickr.com/photos/good_day/



Entropy uestions Wal1throughEntropy uestions Wal1through

S = -Ssys +GHvap

T

: -11J G



et.s look at an e7ample of a

change &e try to e7pect the

outcomeof!

CdiamondCgraphite

Sdiamond :;!>()*#mol*#

Sgraphite :7!B()

*#

mol

*#

What can entropyWhat can entropy notnottell us about?tell us about?

Sreaction= Sproducts- Sreactants

Sreaction=4!I K ;!



istorically)chemistsusedto think

that reactions &ere dri"en %y a

need to mo"e to a lo&er) more

sta%leenergystate!eno&kno&

that this is only half the story

%ecause &e see endothermic

changeshappeningallthetime!

e."e seen that entropy is the dri"ing

factor %ehind changes that occur around

us and &e ha"e seen ho& that can %e

connectedtoenthalpychanges!

#s chemists) it &ould %e useful to us to

e7press the chances of a reaction

happening spontaneously in terms of the

entropyandenthalpychangesoccurring

inthesystem!

Ssurr= Hsurr

T

S = Ssys+ Ssurr

Cinimising Energy or Ca-imising Entropy?Cinimising Energy or Ca-imising Entropy?

Out of copyright
http://commons.wikimedia.org/wiki/File:JosephWright-Alchemist.jpghttp://commons.wikimedia.org/wiki/File:JosephWright-Alchemist.jpghttp://commons.wikimedia.org/wiki/File:JosephWright-Alchemist.jpg



,or spontaneous reaction) the entropy

oftheuni"ersemustincrease

Ssurr= Hsurr

TS = Ssys+ Ssurr > 0 >1?

>2?

The entropy of the surroundings is

increased%ythereleaseofheatenergy

Su%stitute>2?into>1? S

sys

+ Hsurr

> 0

T

ultiply%yT TSsys+ Hsurr > 0

TSsys- Hsys > 0Surroundingsisnegati"eofsystem

Rearranging 0 > H - TS = G

Dibbs Free EnergyDibbs Free Energy

k mo!1/



D

100M Reactants

0M roducts

0M Reactants

100M roducts40540 mi7

/rogress of Reaction

D

100M Reactants

0M roducts

0M Reactants

100M roducts40540 mi7

/rogress of Reaction

G = H T

S$f GN 0 9 reaction spontaneous$f G 0 9 re"erse reaction spontaneous

$f G: 0 9 reaction is at euili%rium

Dibbs Free EnergyDibbs Free Energy

L

L

++



Engorge yourself in entropy at http6entropysite!o-y!edu and

http955secondla&!o7y!edu5 - this page is a good place to start9

http955entropysite!o7y!edu5studentsFapproach!html

Chemistry3 introducin! inor!anic" or!anic and physical chemistry)

urro&s)riceetalKO7ford'ni"ersityress200P

+ummary+ummary

Further ReadingFurther Reading

Entropyincreases&ithincreasingtemperatureandasthestateofasu%stancemo"esfromsolidto

liuidtogas!S5 Gsho&only&hetherareactionisfeasi%leKtheycannotsayho&fastthatreactionislikelyto

proceed

The Second a& of Thermodynamics9 $n a spontaneous process) the entropy of the 'ni"erse

increases! S = Ssys+ Ssurr > 0 for spontaneous change

The Li%%s ,ree Energy >the useful energy a"aila%le to do &ork? &ill %e less than Bero for

spontaneous change(0 > H - TS = G#

I 8 dit
http://entropysite.oxy.edu/http://secondlaw.oxy.edu/http://entropysite.oxy.edu/students_approach.htmlhttp://entropysite.oxy.edu/students_approach.htmlhttp://secondlaw.oxy.edu/http://entropysite.oxy.edu/



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georgeogoodman

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feed%ack on and input into

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