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PHYSICAL

CHEMISTRY 

SMJC 2233

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The direci!n !" chemical

reaci!n# The total energy of the universe isconstant, an so is the energy of anyisolate system.

!ut energy can change form, an thisha""ens in both chemical an"hysical changes.

 Thermoynamics, in its more com"letean #uantitative form, can tell you in$hich irection such changes $ill go.

%t $ill not tell you how fast  they $ill go&

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$ir# La% !"Them!dynamic#

• any change in inernal energy, ∆U, of a system is e#ual to the sum ofthe $or( one on the system an theheat )o$ into the system.

• energy cannot be create orestroye, it can only be transformefrom one form to another

*

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There i# a relai!n#hi& be%een %!r' ()*+Hea (,* and he inernal ener-y (.* !" a#y#em a# "!ll!%#/

0. 1 , )

Thu#+ , and ) are &!#iie i" ener-yran#"erred in! he #y#em a# %!r' !r hea 4, and ) are ne-aie i" ener-y i# l!#5

In an!her %!rd#+ %e ie% he 6!% !" ener-ya# %!r' !r hea "r!m he #y#em7#&er#&ecie5

  The $ir# La% !" Therm!dynamic#

4

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Ener-y

The ener-y !" a #y#em i# i# ca&aciy ! d! %!r'5

)hen %!r' i# d!ne !n a #y#em+ i# ca&aciy !d! %!r' i# increa#ed+ #! he ener-y !" he#y#em i# increa#ed5

)hen he #y#em d!e# %!r'+ i# ener-y i#reduced5

In #ummary+ %hen %!r' i# d!ne !n a #y#em()1&!#iie*+ #! he ener-y increa#e# (!r%e can #ay+ inernal ener-y+ 0. 1 &!#iie*5

5

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The Inernal Ener-y

The !al ener-y !" a #y#em i# called heinernal ener-y+ .5

. i# he !al 'ineic &!enial ener-y !" hem!lecule# c!m&!#in- he #y#em5

The chan-e in inernal ener-y+ 0.+ i# hedi8erence in inernal ener-y be%een %! #ae#5

I mean# ha+ %hen he #y#em chan-e# "r!miniial #ae i %ih he inernal ener-y+ . i  ! a9nal #ae " %ih he inernal ener-y+ ." /

0. 1 ."  : .i  

6

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E;&an#i!n )!r'

 E;&an#i!n %!r' i# he %!r' ari#in- "r!m a chan-e in

!lume5

 $!r e;am&le+ a# #h!%n in he $i-ure+ %hen a &i#!n !"area A m!e# !u hr!u-h a di#ance d

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E;&an#i!n )!r'

The e;ernal &re##ure+ Pe; i# e,uialen !a %ei-h &re##in- !n he &i#!n+ he "!rce!&&!#in- e;&an#i!n i# $1Pe;A5

  Pe; (he e;ernal &re##ure* i# he &re##urea&&lied !n he #y#em "r!m !u#ide he#y#em5 Thu#/

+

  f  

i

V 

exV W dV = − Ρ ∫ 

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E;&an#i!n a-ain# C!n#an Pre##ure

A a c!n#an e;ernal&re##ure hr!u-h!u hee;&an#i!n/) 1 : Pe; 0= 1 Pe; (=i > =" *

$!r e;am&le+ a# #h!%n in$i-ure+ he %!r' d!ne bya -a# %hen i e;&and#a-ain# a c!n#ane;ernal &re##ure+ i#

e,ual ! he #haded area5

A chemical e;am&le !"hi# c!ndii!n i# hee;&an#i!n !" a -a#

"!rmed in a chemical

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Reer#ible E;&an#i!n

  Sy#em a e,uilibrium are &!i#ed !under-! reer#ible chan-e5

 Here+ Pe; i# c!ninu!u#ly chan-in- bu i#

neer "ar "r!m he &re##ure !" he #y#emi#el"5

 In reer#ible e;&an#i!n+ Pe; 1 P#y# > dP ?

P#y# 

 Thu#+ d) 1 :Pe; d= 1 :P#y#d=

10

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 ue#i!n5 A #am&le c!n#i#in- !" B m!l !" Ar-!n i#e;&anded i#!hermally a °C "r!m 225D dm3  ! DD5dm35 Calculae %!r' "!r each "!ll!%in- &r!ce##e#/

 reer#ibly/

) 1 : nRT ln (=" @ =i*  1 : (B m!l* (53BD JK :Bm!l:B* (2F3 K* ln (DD5 @ 225D* 1

: BGF3 J

A-ain# a c!n#an e;ernal &re##ure e,ual ! he9nal &re##ure !" he -a#/

) 1 :P" 0= %hereP" 1 nRT @ =" P" 1 (B m!l* (53BD JK 

:Bm!l:B* (2F3 K* @ DD5 dm3 1 G5 Jdm:3

 0= 1 =

" :=

i 1 DD5 : 225D dm3 1 225D dm3

  12

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Plea#e d! rei#i!n !n 

erfect as /Pa-e 3B!oyles a$ /constant tem"erature

an3harles a$ /constant "ressure

Pa-e 32H!me%!r' Pa-e GD

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ome$or(&

• age 104

 – 2.*/!

 – 2.4/!

 –

2.5/! – 2.6/!

 – 2c.1b

 – 2!.2/b

 – 2!.*/b

 – 2c6.b "art /i

 – 2c7.b

 – 2c+.b

14

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In any naurally !ccurrin- #y#em heenr!&y !" an i#!laed #y#em cann!decrea#e5

a#ed !n he 2

nd

 la% !" herm!dynamic#+hea can be ran#"erred #&!nane!u#lyNLY   "r!m a b!dy a a hi-herem&eraure ! a b!dy a a l!%erem&eraure5

The c!nce& !" enr!&y i# u#ed !de#cribe he de-ree !" !rder in a#y#em5 The number !" %ay# a #y#emcan be !r-ani

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 Hea Ca&aciy a C!n#an =!lume (C=*

 A a c!n#an !lume/ d. 1 d,= 1 C=dT

 $!r polyatomic -a#e#+ he m!lar hea ca&aciy aa c!n#an !lume i# C+m1 2G JK :B m!l:B5

  $!r monoatomic  &er"ec -a#e#+ he m!lar heaca&aciy a a c!n#an !lume+ C+m1 (3@2*R5

16

V 

V 

T 

U C     

 

 

 

 

∂

∂=

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Enhal&y (H*

17

U V Η = + Ρ  

  p

 P 

 P 

C 

C 

∂Η   =  ÷∂Τ  

∆Η = ∆Τ

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1+

ue#i!n5ne m!le !" an ideal m!n!a!mic -a# a 2G5C i# c!!led andall!%ed ! e;&and "r!m B5 dm3 ! B5 dm3 a-ain# ane;ernal &re##ure !" B5 bar5 Calculae he 9nal em&eraure+

%!r'+ hea+ inernal ener-y chan-e and enhal&y chan-e !"hi# &r!ce##5 (R 1 53BD ; B:2 dm35bar5K :B5m!l:B5*An#%er/P= 1 nRTB bar (B dm3* 1 B m!l (53BD;B:2 dm35bar5K :B5m!l:B* TThu#/ T 1 B253 K 

B bar 1 BG Nm:2 Thu#/ B J 1 B Nm % 1 Pe; (=i > =" * 1 BG Nm:2 (B;B:3 m3 > B;B:3 m3* 1 :O J$!r m!n!a!mic -a#+ C+m 1 (3@2*R

 . 1 nC+m  T 1 B m!l ; 3@2 (53BD J5m!l:B5K :B* (B253 K >2O K* 1 :22B5B J, 1 . > % 1 :22B5B J > (: O J* 1 F35O J H 1 . P= 1 : 35F 'J

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1

The Enhal&y !" a Per"ec a#

$!r an Ideal a# he relai!n#hi& be%een heaca&aciie# i# -ien by/

C&:C 1 nR

 g 

V nRU V 

U nR

U n R

Ρ = Τ

Η = + Ρ  

Η = + Τ

∆Η = ∆ + ∆ Τ

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Therm!chemi#ry

20

The #udy !" he ener-y ran#"erred a# headurin- he c!ur#e !" chemical reaci!n5

I" %e 'n!% 0. !r 0H "!r a reaci!n+ %e can&redic he am!un !" hea he reaci!n can&r!duce5

Sandard enhal&y chan-e The chan-e in

enhal&y "!r a &r!ce## in %hich he iniial and9nal #ub#ance# are in heir #andard #ae#5

Sandard #ae i# &ure "!rm a B bar

He## Q# la%/ The #andard enhal&y chan-e !" an!erall reaci!n i# he #um !" he #andard

enhal&ie# !" he indiidual reaci!n# in! %hich areaci!n may be diided5

Pr Re tanr m m

oducts ac ts

ν ν ∆ Η = Η − Η  

∑ ∑

o o o

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Enr!&y

ntro"y is a measure of the energy is"erse in a"rocess.

  The conce"t of entro"y is use to escribe the

egree of orer in a system.

 The number of $ays a system can be organiecan be use as a measure of its isorer or

ranomness

 The secon la$ of thermoynamics uses entro"yto ientify the s"ontaneous changes among

"ermissible changes.

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Enr!&y ny s"ontaneous /natural change in an isolate

system is accom"anie by an increase in theentro"y of the system.

ll s"ontaneous "rocesses are irreversible"rocesses an Total entro"y $hich is the sum ofthe entro"y of the system "lus the surrouningmust be 8 0.

9or reversible "rocess, 0S total = 0S #y#0S#ur1

$!r adiabaic chan-e+ 0S#urr 1 (no heat istransferred to surr.) 22

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S&!nane!u# Pr!ce##e#

2*

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The Therm!dynamic# e9nii!n !" Enr!&y

I !ccur# a# a re#ul !" a &hy#ical !r a chemical chan-e(-enerally/ a &r!ce##*

I c!me# "r!m he idea ha h!% much ener-y i#ran#"erred a# hea5

)hy I i# becau#e hea #imulae# rand!m m!i!n inhe #urr!undin-#5

)!r' #imulae# uni"!rm m!i!n !" a!m# in he

#urr!undin-#+ hu# i d!e#n7 chan-e heir enr!&y5

The enr!&y !" all &er"ec cry#alline #ub#ance# i#

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Enr!&y and reer#ibiliy

9or a reversible "rocess, the entro"y change ise:ne as&

Reversible& a "rocess $here a tiny change inconitions $oul reverse the "rocess.

;uring a reversible "rocess, the system remainsat e#uilibrium. /systems at e#. tens to unergoreversible change

ntro"y generate ue to irreversibility

 ∆S < W lost !  

T 

qS    rev=∆

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=n a $arm evening, 27o3, >ara an li aresitting outsie having a co?ee an $atchingtheir young cousin, 9ara "laying $ith a ball.

9ara, $ho $eighs 2+ (g, is running after theball. nfortunately she isnt loo(ing $hereshe is going an runs into a tree. 9arabounces o? the tree, lans on the groun

an comes to a com"lete sto". 9ara ha as"ee of + m.s-1 Aust before she hit the tree.Bhat is the change in entro"y of theuniverse ue to this collisionC

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%n this case, 9aras collision is an irreversible "rocess , hermechanical energy /(inetic energy is com"letely lost as thermalenergy, an cannot be change bac( into mechanical energy.

 The change in entro"y of the universe ue to this collision isgiven by&

S 1 W l!# /T  $here !  is the tem"erature anW lost is the $or( lost ue to an irreversible "rocess

The %!r' l!# due ! he c!lli#i!n i# he 'ineic ener-y&rei!u#ly had by $ara

 "# $ E mv 2 < E × 2+ (g × /+ m.s-1 < +6 F.

The chan-e in enr!&y !" he unier#e i#

 ∆S < W lost !  

< +6 F G *00 H   < *.0 F.H -1.

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Sandard Reaci!n Enr!&y

•  The i?erence bet$een the molar entro"ies of the"ure, se"arate "roucts an the "ure se"aratereactants at their stanar states at s"eci:etem"erature.

• Bhere vA are stoichiometric numbers / I for"roucts, - for reactants

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$ree:ener-y $unci!n#

Helmh!l< "ree:ener-y A+

A 1 . > TS

ibb# "ree:ener-y +

  he m!#im&!ran

1 H > TS

1 . P= >TS  1 H : T S

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• 3riteria of s"ontaneous change &

dA + (a c!n#an em&5 and!l5*

d (a c!n#an em&5 and&re#5*

)e are m!re inere#ed in chan-e# !ccurrin-a c!n#an &re##ure raher han c!n#an

!lume5

Chemical reaci!n# are #&!nane!u# in hedireci!n !" decrea#in- ibb# Ener-y5

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Helmh!l< Ener-y

• t e#uilibrium, $hen neither thefor$ar nor reverse "rocess has atenency to occur, is&

d AT,V  1

•  The change in the elmholt functionis e#ual to the maJimum $or(accom"anying a "rocess at constanttem"erature&

dwma; 1 d A

=*1

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ibb# $ree Ener-y

• =r sim"ly 9ree nergy

• wa,maJ < %, (maximum additional non&expansionwor')

• wa,maJ $ ∆%

• ∆r G = ∆r  H K − T ∆r S K /standard %ibbs energy of reaction• criterion for e#uilibrium is that the total ibbs 9ree

nergy of a reaction is at a minimum.

• reaction in the irection of ecreasing is s"ontaneous

• reaction in the irection of increasing is nots"ontaneous

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**

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*4

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*5

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E,uilibrium c!n#an

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E;am&le

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Summary

•

Therm!dynamic Pr!&erie# .+H+ S+ A+ • $ir# La% L uses internal energy to

ientify "ermissible changes.• Sec!nd La% L uses entro"y to

ientify s"ontaneous changes among

those "ermissible changes.