Review

1
Review
?Ssystem
gt 0
?Ssurroundings
?Suniverse
for spontaneous processes
?Ssurroundings
energetic disorder
?Ssystem
positional disorder
2
-
?Ssystem ?Ssurroundings ?Suniverse
gt 0
for spontaneous processes
H2O(s) ? H2O(l)
at 298 K
spontaneous
?Ssurroundings
??H gt 0
??Ssurr
lt 0
?Ssurr does not contribute to spontaneity
3
-

?Ssystem ?Ssurroundings ?Suniverse
for spontaneous processes
H2O(s) ? H2O(l)
at 298 K
spontaneous
solid ? liquid
increasing disorder
?S
gt 0
?S
positional disorder
?S does contribute to spontaneity
4
-

?Ssystem ?Ssurroundings ?Suniverse
H2O(s) ? H2O(l)
?S
- ?H / T
solid ? liquid
endothermic
positive
negative
At high T
?Suniv
gt 0
At low T
?Suniv lt 0
5
?Suniverse ?Ssystem ?Ssurroundings gt 0

? N2O4 (g)
2NO2 (g)
NO2 - brown, toxic gas
N2O4 - colorless gas
?Ssurr - ?H / T
?H
- 2 ?Hof NO2
?Hof N2O4
(9.66)
-
(33.5)
-58 kJ mol-1
2

?Ssurr 0
favors spontaneity
gt
6
?Suniverse ?Ssystem ?Ssurroundings gt 0

-
2NO2 (g) ? N2O4 (g)
?S
Soproducts
- Soreactants
So (J mol-1 K-1) N2O4 NO2
304.18
239.95
?S
-175.7 J/mol K
- (239.95)
304.18
2
non-spontaneous
2 mol gas ? 1 mol gas
7

-
?Suniverse ?Ssystem ?Ssurroundings gt 0
2NO2 (g) ? N2O4 (g)
?S
-?H / T
58 kJ mol-1 T(K)
-175.7 J mol-1 K-1
At high T
At low T
8
Free Energy
G
?Ssystem ?Ssurroundings ?Suniverse gt 0
gt 0
- ?H T
?S
?Suniverse
- T
?H -
lt 0
T?S
- T?Suniverse
G ?
H - TS
?H
- T?S
?G
9
?G ?H - T?S
spontaneous reaction
?G lt 0
non-spontaneous reaction
?G gt 0
equilibrium
?G 0
maximum useful work
?G wmax
?G is an extensive State function
?Gof 0
elements in standard states
?Gorxn
?Gof products
- ?Gof reactants
10
?G ?H - T?S
calculate ?Go for
CH4 (g)
2O2 (g)
? CO2 (g)
2H2O (l)
??Gorxn
??Gof CO2 (g)
(?Gof H2O (l))
2
-

?Gof CH4 (g)
2(?Gof O2 (g))
- 819 kJ
??Gorxn ??Horxn - T?Sorxn
-892 kJ
-

(298K)
(-242 J/K)
-819 kJ
11
Rubber band Thermodynamics
State 1 relaxed
State 2 stretched
go from State 1 to State 2
What is sign of ?Go

-
What is sign of ?Ho
What is sign of ?So
?Go ?Ho - T?So
-
-

12
?Go ?Ho - T?So
?Ho
?So
?Go
-
always positive
-
always negative
negative
high T

positive
low T
- -
negative
low T
positive
high T
13
Equilibrium
?Go ?Ho - T?S
?Go 0
phase changes
chemical reactions
?Ho
?So
?Ho-
?Ho
T?So 0
?Hof prod -
?Hof react
T
?Ho
T
___________________________
Soprod -
Soreact
-58 kJ
2NO2 ? N2O4
331 K
-175.7 J/K
14
Napoleon - 1812
tin buttons
?Hof (kJ/mol)
So (J/mol K)
white tin
0.0
51.55
grey tin
-2.1
44.14
?Ho
-2.1
- 0.0
-2.1 kJ
Snwhite
Sngrey
?
?So
44.14
- 51.55
-7.4 J/mol K
T
-2100 J
283 K
10oC
-7.4 J/K
?G298 .105 kJ
?G233 -.376 kJ