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ThermodynamicsChapter 18



1st Law of Thermodynamics

Energy is conserved.

∆E = q + w



SP!T"!E#S$ occ%r witho%tany o%tside intervention

E&amp'e$ drop an egg

The (E)E(SE is not spontaneo%s**



(E)E(S,LE P(CESS$ change

can -e restored to its origina' state -y e&act'y reversing the change .

E&amp'e$ ice water at /o C



((E)E(S,LE P(CESS$

cannot simp'y -e reversed toorigina' state.

E&amp'e$ gas e&panding



Processes in which the

disorder of the system

increases tend to occ%rspontaneously.

E&$ gas e&panding0 ice me'ting0 sa't disso'ving



E!T(P$ 2S3 the change in

disorder. 2Change in randomness3The more disorder0 the 'arger the

entropy.

∆S = Sfina' 4 Sinitia'



∆S = 5 / when the fina' state is

in more disorder

∆S = 6 / when the fina' state

is more ordered than origina'



7 2'3 ⇔ 7 2s3

"g

+

2aq3 + C'

4

2aq3

→ "gC'2s3



4 a so'id me'ts

4 a 'iq%id vapori9es

4 a so'id disso'ves in water

4 a gas 'iq%efies



:or a process at constant

temperat%re0 the entropychange is the va'%e of qrev

divided -y the a-so'%tetemperat%re.

∆S = qrev;T



E&amp'e$ Ca'c%'ate the entropy

change when 1 mo' of water isconverted into 1 mo' of steam at

1 atm press%re. 2∆7vap = </.>?@;mo'3



21 mo'e32</.> ?@; mo'321/// @;1 ?@3

A>A B

∆S = 1/ @;B



The norma' free9ing point of

merc%ry is 4A8.oC0 an itsmo'ar entha'py of f%sion is

∆7f%s = .AA1 ?@;mo'. Dhat is

the entropy change when /./

g of 7g2'3 free9es at the

norma' free9ing pointF



4.<8 @;B The answer is negative -eca%se the

process -rings more order



The norma' -oi'ing point of

ethano'0 is >8.AoC and its mo'arentha'py of vapori9ation is A8.

?@;mo'. Dhat is the change inentropy when .8 g of

C772g3 condenses to 'iq%id atthe norma' -oi'ing pointF



41.< @;B



The e'ement ga''i%m0 Ga0

free9es at .8oC0 and itsentha'py of f%sion is .

?@;mo'. Ca'c%'ate the

va'%e of ∆S for thefree9ing of /./ g of Ga2'3.



∆S = 4A.8 @;B



nd Law of Thermodynamics$ n any

reversi-'e process0∆

S%niverse = /. n anyirreversi-'e 2spontaneo%s3 process0

∆S%niverse 5 /.

∆S%niverse = ∆Ssystem + ∆Ss%rro%ndings



On a Molecular Level

T("!SL"T!"L HT!$ movement of

mo'ec%'es

),("T!"L HT!$ the movement of

atoms within the mo'ec%'e.

(T"T!"L HT!$ the mo'ec%'es

spinning



ncreasing Temperat%re ncreases Entropy



Ard Law of Thermodynamics$ the

entropy of a p%re crysta''ine

s%-stance at a-so'%te 9ero is 9ero.

S2/B3 = /



In general, the entropy increases when$

Liq%ids or so'%tions are formed from so'ids

Gases are formed from either so'ids or

'iq%ids

The n%m-er of mo'ec%'es of gas increasesd%ring a chemica' reaction.



CaCA2s3 → Ca2s3 + C2g3

!2g3 + A72g3 → !7A2g3



Standard molar entropies$ 2So3 a-so'%te

entropies for s%-stances in their standard

state. 2@;mo'4B3

1. #n'i?e entha'pies of formation0 the standard mo'ar

entropies of e'ements are not 9ero.

. The So of gases are greater than those of 'iq%ids and

so'ids.

A. The So genera''y increases with increasing mo'ar mass.

<. The So genera''y increase with the n%m-er of atoms in

the form%'a.



∆So = ΣnSo2prod%cts3

4 ΣmSo2reactants3

Ca'c%'ate ∆So for the synthesis of ammonia$

!2g3 + A72g3 → !7A2g3



∆So = 2 mo'321. @;mo'4B3 4

I21 mo'3211. @;mo'4B3 + 2Amo'321A/. @;mo'4B3J =

418.A @;B



#sing "ppendi& C0 ca'c%'ate the

standard entropy change0 for thefo''owing reaction$

"'A2s3 + A72g3 → "'2s3 + A72g3



18/.< @;B



C

7<2g3

+ 72g3

→ C

72g3

!7A2g3 + 7C'2g3 → !7<C'2s3



41/. @;B

48<. @;B



GIBBS FREE EERG!

The spontaneity of a reaction invo'ves -oth

entha'py and entropy. The re'ationship is

?nown as "ree energy.

∆G = ∆7 4 T∆S



1. f ∆G is negative0 the reaction is

spontaneo%s in the forward direction.

. f ∆G is 9ero0 the reaction is at

eq%i'i-ri%m.

A. f ∆G is positive0 the reaction in the

forward direction is nonspontaneo%sK wor?

m%st -e s%pp'ied from the s%rro%ndings to

ma?e it occ%r. 7owever0 the reverse reaction

wi'' -e spontaneo%s.



∆G



∆Go = ∑n∆Gf o2prod%cts3 4 ∑m∆Gf

o2reactants3

!2g3 + A72g3 → !7A2g3



4AA.A ?@



C7<2g3 + 2g3 → C2g3 + 72g3



C7<2g3 + 2g3 → C2g3 + 72g3

48//.> ?@

" i h f ∆7



"ss%ming no change for ∆7o

and∆

S

o

0 what happens to∆

G

o

with an increase in temperat%reF

!2g3 + A72g3 → !7A2g3

C ' ' ∆G 8B f



Ca'c%'ate ∆G at 8B for

a reaction mi&t%re thatconsists of 1./ atm !0 A./

atm 7 and /./ atm !7A.

!2g3 + A72g3 → !7A2g3



#se standard free energies

of formation to ca'c%'ate

the eq%i'i-ri%m constantB at oC for the reaction

invo'ved in the 7a-er process.