review
DESCRIPTION
= - H sys T. = q r T. Review. S system. + S surroundings. = S universe. > 0. for spontaneous processes. S surroundings. energetic disorder. S system. positional disorder. = - H T. -. S system + S surroundings = S universe. > 0. - PowerPoint PPT PresentationTRANSCRIPT
ReviewSsystem
for spontaneous processes
> 0
Ssurroundings energetic disorder= - Hsys
T
Ssystem = qr
T
positional disorder
+ Ssurroundings = Suniverse
Ssystem + Ssurroundings = Suniverse
for spontaneous processes
> 0
Ssurroundings = - H
T
H2O(s) H2O(l)at 298 K spontaneous
H > 0
Ssurr < 0
-
Ssurr does not contribute to spontaneity
Ssystem + Ssurroundings = Suniverse
for spontaneous processes
H2O(s) H2O(l)at 298 K spontaneous
-
S positional disorder
solid liquid increasing disorder
S > 0
+
S does contribute to spontaneity
Ssystem + Ssurroundings = Suniverse
H2O(s) H2O(l)
solid liquidpositive
S
endothermicnegative
- H / T
At high T
At low T
Suniv
Suniv < 0
> 0
-+
Suniverse= Ssystem+ Ssurroundings > 0
2NO2 (g)
NO2 - brown, toxic gasN2O4 - colorless gas
Ssurr = - H / T
H
= (9.66)
Ssurr 0 favors spontaneity
- 2 Hof NO2
-58 kJ mol-1
= Hof N2O4
N2O4 (g)
+
- (33.5)2 =
>
2NO2 (g) N2O4 (g)
S =
So (J mol-1 K-1)N2O4
NO2
304.18239.95
S - (239.95)]= -175.7 J/mol K
2 mol gas 1 mol gas non-spontaneous
= [304.18 2
Soproducts - So
reactants
+Suniverse= Ssystem+ Ssurroundings > 0
-
2NO2 (g) N2O4 (g)
+Suniverse= Ssystem+ Ssurroundings > 0
-
-175.7 J mol-1 K-1
S -H / T+58 kJ mol-1
T(K)At high T
At low T
Free Energy
Ssystem+ Ssurroundings = Suniverse > 0
S
H -
G
GG
- H T
= Suniverse> 0
< 0TS = - TSuniverse
H - TS
= = HH - - TTSS
GG
- T
G = H - TS
G < 0
G > 0
G = 0
G = wmax
G is an extensive State function
Gof = 0
Gorxn =
spontaneous reaction
non-spontaneous reaction
equilibrium
maximum useful work
elements in standard states
Gof products - Go
f reactants
GG = = HH - - TTSScalculate Go for:
CH4 (g)
Gorxn =
- [ ]
= - 819 kJ
Gorxn = Ho
rxn - TSorxn
[Gof CO2 (g)+ ]
= [-892 kJ]-[ ](298K) (-242 J/K) = -819 kJ
+ 2O2 (g) CO2 (g) + 2H2O (l)
(Gof H2O (l))2
Gof CH4 (g) + 2(Go
f O2 (g))
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 - TSo ++ -- --
++
GGoo = = HHoo - T - TSSoo
HHoo
++ --
-- ++
++ ++
-- --
positive
always positive
always negative
negative
negative
positive
high T
low T
SSoo GGoo
low T
high T
Equilibrium
Go = Ho - TS Go = 0
Ho
phase changes
Ho Hof prod -
___________________________
Soprod -= T
TSo = 0 = So
T
T = So
Ho- Ho
Hof react
Soreact
2NO2 N2O4-58 kJ
-175.7 J/K= 331 K
chemical reactions
tin buttons
Napoleon - 1812
white tin
ΔHof (kJ/mol) So (J/mol K)
grey tin0.0 51.55
-2.1 44.14
Snwhite SngreyΔHo = -2.1 - 0.0 = -2.1 kJ
ΔSo = 44.14 - 51.55= -7.4 J/mol K
T = -2100 J
-7.4 J/K
= 283 K = 10oC
∆G298 = .105 kJ ∆G233 = -.376 kJ