IB Chemistry on Gibbs Free Energy, Equilibrium constant and Cell Potential

1. cellnFEG  
Relationship between
Energetics and Equilibrium
cKRTG ln 
STHG 
Enthalpy
change
Entropy
change
Equilibrium
constant
Gibbs free
energy change
H
G
Relationshipbet ∆G, Kc and E cell
cellnFEG  
STHG  cKRTG ln 
cK
Relationship between
Energetics and Cell Potential

G cellE
Gibbs free
energy change
Cell potential
F = Faraday constant
(96 500 Cmol-1)
n = number
electron
Relationship bet ∆G, Kc and Ecell
ΔGθ Kc Eθ/V Extent of rxn
> 0 < 1 < 0 No Reaction
Non spontaneous
ΔGθ = 0 Kc = 1 0 Equilibrium
Mix reactant/product
< 0 > 1 > 0 Reaction complete
Spontaneous
ΔGθ Kc Eq mixture
ΔGθ = + 200 9 x 10-36 Reactants
ΔGθ = + 10 2 x 1-2 Mixture
ΔGθ = 0 Kc = 1 Equilibrium
ΔGθ = - 10 5 x 101 Mixture
ΔGθ = - 200 1 x 1035 Products
Relationship bet ∆G and Kc
shift to left (reactant)
shift to right (products)
cellE

G
cK
K
nF
RT
E cell ln

2. Magnitudeof Kc
Extendof reaction
How far rxn shift to right or left?
Not how fast
cK
Positionof equilibrium
cK
Temp
dependent
Extend
of rxn
Not how fast
Shift to left/
favour reactant
Shift to right/
favour product
cK
Relationship between
Equilibrium and Energetics
cKRTG ln 
STHG 
Enthalpy
change
Entropy
change
Equilibrium
constant
Gibbs free energy change
H
G cK
G
Energetically
Thermodynamically
Favourable/feasible
ΔGθ ln K Kc Eq mixture
ΔGθ -ve
< 0
Positive
( + )
Kc > 1 Product
(Right)
ΔGθ +ve
> 0
Negative
( - )
Kc < 1 Reactant
(left)
ΔGθ = 0 0 Kc = 1 Equilibrium
Measure work
available from system
Sign predict
spontaneity of rxn
Negative (-ve)
spontaneous
Positive (+ve)
NOT
spontaneous
veG  veG 
NOT
favourable
Energetically
favourable
Product formation NO product
cKRTG ln 

3. Magnitudeof Kc
Extendof reaction
How far rxn shift to right or left?
Not how fast
cK
Positionof equilibrium
cK
Temp
dependent
Extend
of rxn
Not how fast
Shift to left/
favour reactant
Shift to right/
favour product
cK
Relationship between
Equilibrium and Energetics
cKRTG ln 
STHG 
Enthalpy
change
Entropy
change
Equilibrium
constant
Gibbs free energy change
H
G cK
ΔGθ ln K Kc Eq mixture
ΔGθ -ve
< 0
Positive
( + )
Kc > 1 Product
(Right)
ΔGθ +ve
> 0
Negative
( - )
Kc < 1 Reactant
(left)
ΔGθ = 0 0 Kc = 1 Equilibrium
cKRTG ln 
STHG 
∆Hsys ∆Ssys ∆Gsys Description
- +
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, All Temp
+ -
∆G = ∆H - T∆S
∆G = + ve
Non spontaneous, All Temp
+ +
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, High ↑ Temp
- -
∆G = ∆H - T∆S
∆G = - ve
Spontaneous, Low ↓ Temp
Relationshipbet ∆G and Kc

4. G
Energetically
Thermodynamically
Favourable/feasible
Sign predict
spontaneity of rxn
veG  veG 
NOT
favourable
Energetically
favourable
Product formation NO product
KRTG ln
Predictwill rxn occur with ΔG and Kc
cK
Very SMALL
Kc < 1
Shift to right/
favour product
Shift to left/
favour reactant
Very BIG
Kc > 1
veG veG 
KRTG ln
1cK 1cK
Negative (-ve)
spontaneous
Positive (+ve)
NOT
spontaneous
Relationship bet ∆G and Kc
ΔGθ Kc Eq mixture
ΔGθ = + 200 9 x 10-36 Reactant
ΔGθ = + 10 2 x 1-2 Mixture
ΔGθ = 0 Kc = 1 Equilibrium
ΔGθ = - 10 5 x 101 Mixture
ΔGθ = - 200 1 x 1035 Products
shift to left (reactant)
shift to right (product)
G, Gibbs free energy
A
Mixture composition
B
100% A 100% B
∆G decreases ↓
30 % A
70 % B
Equilibrium mixture
∆G < 0
∆G = 0 (Equilibrium)
↓
Free energy minimum
∆G < 0
∆G < 0
∆G = 0
Free energy system is lowered on the way to equilibrium
Rxn proceed to minimum free energy ∆G = 0
System seek lowest possible free energy
Product have lower free energy than reactant
∆G < 0 product
reactant

5. G
Energetically
Thermodynamically
Favourable/feasible
Sign predict
spontaneity of rxn
veG  veG 
NOT
favourable
Energetically
favourable
Product formation NO product
KRTG ln
cK
Very SMALL
Kc < 1
Shift to right/
favour product
Shift to left/
favour reactant
Very BIG
Kc > 1
veG veG 
KRTG ln
1cK 1cK
Negative (-ve)
spontaneous
Positive (+ve)
NOT
spontaneous
Relationship bet ∆G, Q and Kc
G, Gibbs free energy
A
B
100% A 100% B
∆G decreases ↓
30 % A
70 % B
Equilibrium mixture
∆G < 0
∆G = 0 (Equilibrium)
↓
Free energy
minimum
∆G < 0
∆G < 0
∆G = 0
∆G < 0 product
reactant
G, Gibbs free energy
reactant product∆G < 0
A
B
∆G decreases ↓
100% A 100% B30 % A
70 % B
∆G = 0
Q = K
∆G < 0
Q < K
∆G > 0
∆G < 0
Q > K
∆G > 0
A ↔ B A ↔ B
Equilibrium mixture
Predictwill rxn occur with ΔG and Kc

6. Relationship bet ∆G and Kc
G, Gibbs free energy
A
B
100%
A
100%
B
∆G decreases ↓
30 % A
70 % B
Equilibrium mix close to product
∆G < 0
∆G = 0 (Equilibrium)
↓
Free energy minimum
∆G < 0
∆G < 0
∆G = 0
∆G < -10
Kc > 1
A ↔ B A ↔ B
G, Gibbs free energy
A
B
∆G decreases ↓
∆G < -100
100%
A
100%
B
∆G = 0 (Equilibrium)
↓
Free energy minimum
Kc > 1Equilibrium mix close to product
10 % A
90 % B
∆G < 0
∆G < 0 ∆G = 0
∆G very –ve → Kc > 1 → (more product/closeto completion)∆G –ve → Kc > 1 → (more product > reactant)
A ↔ B
G, Gibbs free energy
100%
A
100%
B
A
B
∆G +ve → Kc < 1 → (more reactant > product)
∆G > +10
∆G = 0 (Equilibrium)
↓
Free energy minimum
Kc < 1
∆G increases ↑
70 % A
30 % B
Equilibrium mix close to reactant
∆G < 0
∆G = 0
A ↔ B
G, Gibbs free energy
∆G more +ve → Kc < 1 → (All reactant / no product at all)
A
∆G = 0 (Equilibrium)
↓
Free energy minimum
Kc < 1100%
A
100%
B
Equilibrium mix close to reactant/ No reaction.
∆G > +100
B
90 % A
10 % B
∆G increases ↑
∆G = 0
∆G < 0
reactant
reactant
reactant
reactant
productproduct
product product

7. Relationship bet ∆G and Kc
shift to left (reactant)
shift to right (product)
G, Gibbs free energy
A
B
100%
A
100%
B
∆G decreases ↓
30 % A
70 % B
Equilibrium mixture
∆G < 0
∆G = 0 (Equilibrium)
↓
Free energy minimum
∆G < 0
∆G < 0
∆G = 0
Free energy system is lowered on the way to equilibrium
Rxn proceed to minimum free energy ∆G = 0
System seek lowest possible free energy
Product have lower free energy than reactant
∆G < -10
Kc > 1
A ↔ B A ↔ B
G, Gibbs free energy
A
B
∆G decreases ↓
∆G < -100
100%
A
100%
B
∆G = 0 (Equilibrium)
↓
Free energy minimum
Kc > 1Equilibrium mixture
10 % A
90 % B
∆G < 0
∆G < 0 ∆G = 0
∆G very –ve → Kc > 1 → (All product/closeto completion)∆G –ve → Kc > 1 → (more product > reactant)
∆G
∆G = 0
∆G > 0
∆G < 0
No reaction/most reactants
Kc <1
Complete rxn/Most products
Kc > 1
Kc = 1 (Equilibrium)
Reactants= Products
reactant
reactant
ΔGθ Kc Eq mixture
ΔGθ = + 200 9 x 10-36 Reactant
ΔGθ = + 10 2 x 1-2 Mixture
ΔGθ = 0 Kc = 1 Equilibrium
ΔGθ = - 10 5 x 101 Mixture
ΔGθ = - 200 1 x 1035 Products

8. 298314.8
)212000(
ln





RT
G
Kc
Zn ↔ Zn2+ + 2e Eθ = +0.76
Cu2+ + 2e ↔ Cu Eθ = +0.34
Zn + Cu2+ → Zn 2+ + Cu Eθ = +1.10V
Zn half cell (-ve)
Oxidation
Cu half cell (+ve)
Reduction
Anode Cathode
Zn(s) | Zn2+
(aq) || Cu2+
(aq) | Cu (s)
Cell diagram
Anode Cathode
Half Cell Half Cell
(Oxidation) (Reduction)
Salt Bridge Flow
electrons
Zn/Cu Voltaic Cell
-e -e
Zn/Cu half cells
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Eθ
cell = +0.34 – (-0.76) = +1.10V
Zn 2+ + 2e ↔ Zn (anode) Eθ = -0.76V
Cu2+ + 2e ↔ Cu (cathode) Eθ = +0.34V
Std electrode potential as std reduction potential
Find Eθ
cell (use reduction potential)Find Eθ
cell (use formula)
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Zn 2+ + 2e ↔ Zn Eθ = -0.76V
Cu2+ + 2e ↔ Cu Eθ = +0.34V
Oxidized sp ↔ Reduced sp Eθ/V
Li+ + e- ↔ Li -3.04
K+ + e- ↔ K -2.93
Ca2+ + 2e- ↔ Ca -2.87
Na+ + e- ↔ Na -2.71
Mg 2+ + 2e- ↔ Mg -2.37
Al3+ + 3e- ↔ AI -1.66
Mn2+ + 2e- ↔ Mn -1.19
H2O + e- ↔ 1/2H2 + OH- -0.83
Zn2+ + 2e- ↔ Zn - 0.76
Fe2+ + 2e- ↔ Fe -0.45
Ni2+ + 2e- ↔ Ni -0.26
Sn2+ + 2e- ↔ Sn -0.14
Pb2+ + 2e- ↔ Pb -0.13
H+ + e- ↔ 1/2H2 0.00
Cu2+ + e- ↔ Cu+ +0.15
SO4
2- + 4H+ + 2e- ↔ H2SO3 +0.17
Cu2+ + 2e- ↔ Cu + 0.34
1/2O2 + H2O +2e- ↔ 2OH- +0.40
+
+1.10 V
Eθ
Zn/Cu = 1.10V
Cu2+
-
-
-
-
Zn Cu
+
+
+
+
cellnFEG  
E cell with ∆G
F = Faraday constant
(96 500 Cmol-1)
n = number electron
cellnFEG  
kJJG
G
212212300
10.1965002




∆G –ve, E +ve, K > 1
∆G <0, E > 0, K > 1
↓
Rxn SpontaneouscKRTG ln 
Equilibrium
constant
Gas constant, 8.314
∆G with Kc
cKRTG ln  37
103.1 cK
Favour products

9. Zn ↔ Zn2+ + 2e Eθ = +0.76
2Ag++2e ↔ 2Ag Eθ = +0.80
Zn + Ag+ → Zn 2+ + Ag Eθ = +1.56V
Zn half cell (-ve)
Oxidation
Ag half cell (+ve)
Reduction
Anode Cathode
Zn(s) | Zn2+
(aq) || Ag+
(aq) | Ag (s)
Cell diagram
Anode Cathode
Half Cell Half Cell
(Oxidation) (Reduction)
Salt Bridge Flow
electrons
Zn/Ag Voltaic Cell
-e -e
Zn/Ag half cells
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Eθ
cell = +0.80 – (-0.76) = +1.56V
Zn 2+ + 2e ↔ Zn (anode) Eθ = -0.76V
Ag + + e ↔ Ag(cathode) Eθ = +0.80V
Std electrode potential as std reduction potential
Find Eθ
cell (use reductionpotential)Find Eθ
cell (use formula)
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Zn 2+ + 2e ↔ Zn Eθ = -0.76V
Ag+ + e ↔ Ag Eθ = +0.80V
Oxidized sp ↔ Reduced sp Eθ/V
Li+ + e- ↔ Li -3.04
K+ + e- ↔ K -2.93
Ca2+ + 2e- ↔ Ca -2.87
Na+ + e- ↔ Na -2.71
Mg 2+ + 2e- ↔ Mg -2.37
Al3+ + 3e- ↔ AI -1.66
Mn2+ + 2e- ↔ Mn -1.19
H2O + e- ↔ 1/2H2 + OH- -0.83
Zn2+ + 2e- ↔ Zn - 0.76
Fe2+ + 2e- ↔ Fe -0.45
Ni2+ + 2e- ↔ Ni -0.26
Sn2+ + 2e- ↔ Sn -0.14
Pb2+ + 2e- ↔ Pb -0.13
H+ + e- ↔ 1/2H2 0.00
Cu2+ + e- ↔ Cu+ +0.15
SO4
2- + 4H+ + 2e- ↔ H2SO3 +0.17
Cu2+ + 2e- ↔ Cu +0.34
1/2O2 + H2O +2e- ↔ 2OH- +0.40
Cu+ + e- ↔ Cu +0.52
1/2I2 + e- ↔ I- +0.54
Fe3+ + e- ↔ Fe2+ +0.77
Ag+ + e- ↔ Ag + 0.80
1/2Br2 + e- ↔ Br- +1.07
+
+1.56 V
Ag
Eθ
Zn/Ag = +1.56V
Ag+
-
-
-
-
+
+
+
+
Zn
E cell with ∆G
cellnFEG  
n = number electron F = Faraday constant
(96 500 Cmol-1)
cellnFEG  
kJJG
G
301301000
56.1965002




∆G with Kc
cKRTG ln 
Gas constant, 8.314 Equilibrium
constant
cKRTG ln 
298314.8
)301000(
ln





RT
G
Kc
52
105.3 cK
∆G –ve, E +ve, K > 1
∆G <0, E > 0, K > 1
↓
Rxn Spontaneous
Favour products

10. Mn ↔ Mn2+ + 2e Eθ = +1.19
Ni2+ + 2e ↔ Ni Eθ = -0.26
Mn + Ni2+ → Mn2+ + Ni Eθ = +0.93V
Mn half cell (-ve)
Oxidation
Ni half cell (+ve)
Reduction
Anode Cathode
Mn(s) | Mn2+
(aq) || Ni2+
(aq) | Ni (s)
Cell diagram
Anode Cathode
Half Cell Half Cell
(Oxidation) (Reduction)
Salt Bridge Flow
electrons
Mn/Ni Voltaic Cell
-e -e
Mn/Ni half cells
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Eθ
cell = -0.26 – (-1.19) = +0.93V
Mn 2+ + 2e ↔ Mn (anode) Eθ = -1.19V
Ni2+ + 2e ↔ Ni (cathode) Eθ = -0.26V
Std electrode potential as std reduction potential
Find Eθ
cell (use reductionpotential)Find Eθ
cell (use formula)
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Mn 2+ + 2e ↔ Mn Eθ = -1.19V
Ni2+ + 2e ↔ Ni Eθ = -0.26V
Oxidized sp ↔ Reduced sp Eθ/V
Li+ + e- ↔ Li -3.04
K+ + e- ↔ K -2.93
Ca2+ + 2e- ↔ Ca -2.87
Na+ + e- ↔ Na -2.71
Mg 2+ + 2e- ↔ Mg -2.37
Al3+ + 3e- ↔ AI -1.66
Mn2+ + 2e- ↔ Mn -1.19
H2O + e- ↔ 1/2H2 -0.83
Zn2+ + 2e- ↔ Zn -0.76
Fe2+ + 2e- ↔ Fe -0.45
Ni2+ + 2e- ↔ Ni - 0.26
Sn2+ + 2e- ↔ Sn -0.14
Pb2+ + 2e- ↔ Pb -0.13
H+ + e- ↔ 1/2H2 0.00
Cu2+ + e- ↔ Cu+ +0.15
SO4
2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17
Cu2+ + 2e- ↔ Cu +0.34
1/2O2 + H2O +2e- ↔ 2OH- +0.40
Cu+ + e- ↔ Cu +0.52
1/2I2 + e- ↔ I- +0.54
+
+0.93 V
Eθ
Mn/Ni = +0.93V
Ni2+
-
-
-
-
NiMn
+
+
+
+Mn2+
E cell with ∆G
cellnFEG  
n = number electron F = Faraday constant
(96 500 Cmol-1)
cellnFEG  
kJJG
G
179179490
93.0965002




cKRTG ln 
298314.8
)179000(
ln





RT
G
Kc
cKRTG ln 
∆G with Kc
Gas constant, 8.314 Equilibrium
constant
∆G –ve, E +ve, K > 1
∆G <0, E > 0, K > 1
↓
Rxn Spontaneous
31
102.2 cK
Favour products

11. Oxidized sp ↔ Reduced sp Eθ/V
Li+ + e- ↔ Li -3.04
K+ + e- ↔ K -2.93
Ca2+ + 2e- ↔ Ca -2.87
Na+ + e- ↔ Na -2.71
Mg 2+ + 2e- ↔ Mg -2.37
Al3+ + 3e- ↔ AI -1.66
Mn2+ + 2e- ↔ Mn -1.19
H2O + e- ↔ H2 + OH- -0.83
Zn2+ + 2e- ↔ Zn -0.76
Fe2+ + 2e- ↔ Fe -0.45
Ni2+ + 2e- ↔ Ni -0.26
Sn2+ + 2e- ↔ Sn -0.14
H+ + e- ↔ H2 0.00
Cu2+ + e- ↔ Cu+ +0.15
SO4
2- + 4H+ + 2e- ↔ H2S +0.17
Cu2+ + 2e- ↔ Cu +0.34
Cu ↔ Cu2+ + 2e Eθ = -0.34
2H+ + 2e ↔ H2 Eθ = +0.00
Cu + 2H+→ Cu2+ +H2 Eθ = -0.34V
Rxn bet Cu + H+
Will it happen ?
Eθ
= -0.34V
(NON spontaneous)
О
Cu(s) | Cu2+
(aq) || H+ H2 | Pt (s)
(Oxidation) (Reduction)
Anode Cathode
Find Eθ
cell (use formula)
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Eθ
cell = 0.00 – (+0.34) = -0.34V
Eθ
= -0.34V
(NON spontaneous)
О
Rxn not feasible
Determinespontaneityrxn. Will it HAPPEN?
Find Eθ
cell (use reductionpotential)
Eθ
Cu/H+ = - 0.34V
E cell with ∆G
cellnFEG  
n = number electron F = Faraday constant
(96 500 Cmol-1)
cellnFEG  
kJJG
G
6565620
34.0965002




cKRTG ln 
Gas constant, 8.314 Equilibrium
constant
∆G with Kc
cKRTG ln 
298314.8
)65000(
ln





RT
G
Kc
∆G +ve, E -ve, K < 1
∆G >0, E < 0, K < 1
↓
Rxn Non Spontaneous
12
104 
cK
Favour reactants
-0.34 V
acid
copper
Predictingwill rxn occur with ΔG, E cell and Kc
+

12. Oxidized sp ↔ Reduced sp Eθ/V
Li+ + e- ↔ Li -3.04
K+ + e- ↔ K -2.93
Ca2+ + 2e- ↔ Ca -2.87
Na+ + e- ↔ Na -2.71
Mg 2+ + 2e- ↔ Mg -2.37
Al3+ + 3e- ↔ AI -1.66
Mn2+ + 2e- ↔ Mn -1.19
H2O + e- ↔ H2 + OH- -0.83
Zn2+ + 2e- ↔ Zn -0.76
Fe2+ + 2e- ↔ Fe -0.45
Ni2+ + 2e- ↔ Ni -0.26
Sn2+ + 2e- ↔ Sn -0.14
H+ + e- ↔ H2 0.00
Cu2+ + e- ↔ Cu+ +0.15
SO4
2- + 4H+ + 2e- ↔ H2S +0.17
Cu2+ + 2e- ↔ Cu +0.34
Au3+ + 3e- ↔ Au +1.58
Rxn bet Au + H+
Will it happen ?
Eθ
= -1.58 V
(NON spontaneous)
О
Au(s) | Au3+
(aq) || H+ H2 | Pt (s)
(Oxidation) (Reduction)
Anode Cathode
Find Eθ
cell (use formula)
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Eθ
cell = 0.00 – (+1.58) = -1.58V
Eθ
= - 1.58 V
(NON spontaneous)
О
Rxn not feasible
Determinespontaneityrxn. Will it HAPPEN?
Find Eθ
cell (use reductionpotential)
Eθ
Au/H+ = - 1.58V
E cell with ∆G
cellnFEG  
n = number electron F = Faraday constant
(96 500 Cmol-1)
cellnFEG  
kJJG
G
914914820
58.1965006




cKRTG ln 
Gas constant, 8.314 Equilibrium
constant
∆G with Kc
cKRTG ln 
298314.8
)914000(
ln





RT
G
Kc
∆G +ve, E -ve, K < 1
∆G >0, E < 0, K < 1
↓
Rxn Non Spontaneous
50
104 
cK
Kc too small – No reactionat all
-1.58 V
acid
gold
2Au ↔ 2Au3+ + 6e Eθ = -1.58
6H+ + 6e ↔ 3H2 Eθ = 0.00
2Au + 6H+ → 2Au3+ + 3H2 Eθ = -1.58V
+
Predictingwill rxn occur with ΔG, E cell and Kc

13. Eθ
= - 0.20 V
(NON spontaneous)
(Oxidation) (Reduction)
Anode Cathode
Find Eθ
cell (use formula)
Eθ
cell = Eθ
(cathode) – Eθ
(anode)
Eθ
cell = 0.34 – (0.54) = - 0.20V
Eθ
= - 0.20 V
(NON spontaneous)
Determinespontaneityrxn. Will it HAPPEN?
Find Eθ
cell (use reductionpotential)
Eθ
Cu2+/I- = - 0.20V
E cell with ∆G
cellnFEG  
n = number electron F = Faraday constant
(96 500 Cmol-1)
cellnFEG  
kJJG
G
3838600
20.0965002




cKRTG ln 
Gas constant, 8.314 Equilibrium
constant
∆G with Kc
cKRTG ln 
298314.8
)38000(
ln





RT
G
Kc
∆G +ve, E -ve, K < 1
∆G >0, E < 0, K < 1
↓
Rxn Non Spontaneous
7
102.2 
cK
-1.58 V
Cu2+
I-Rxn bet Cu2+ +I-
Will it happen?
2I- ↔ I2 + 2e Eθ = -0.54
Cu2+ + 2e ↔ Cu Eθ = +0.34
2I- + Cu2+→ Cu + I2 Eθ = -0.20V
Pt(s) | I-, I2 || Cu2+
(aq) | Cu (s)
Favour reactants
Oxidized sp ↔ Reduced sp Eθ/V
Li+ + e- ↔ Li -3.04
K+ + e- ↔ K -2.93
Ca2+ + 2e- ↔ Ca -2.87
Na+ + e- ↔ Na -2.71
Mg 2+ + 2e- ↔ Mg -2.37
Al3+ + 3e- ↔ AI -1.66
Mn2+ + 2e- ↔ Mn -1.19
Zn2+ + 2e- ↔ Zn -0.76
Fe2+ + 2e- ↔ Fe -0.45
Ni2+ + 2e- ↔ Ni -0.26
Sn2+ + 2e- ↔ Sn -0.14
H+ + e- ↔ 1/2H2 0.00
Cu2+ + e- ↔ Cu+ +0.15
Cu2+ + 2e- ↔ Cu +0.34
1/2O2 + H2O +2e- ↔ 2OH- +0.40
Cu+ + e- ↔ Cu +0.52
I2 + 2e- ↔ I- +0.54
Rxn not feasible
О
О
- 0.20 V
Will I- oxidize
Cu2+ to Cu
Predictingwill rxn occur with ΔG, E cell and Kc

14. Click here to view free energy
PredictingSpontaneity of Rxn
Thermodynamic,ΔG Equilibrium, Kc
 1cK
 1cK
KRTG ln
G
veG 
cK
1cK
Energetically
favourable
0G
Predictingrxn will occur?
N2(g) + 3H2(g) ↔ 2NH3(g)
H2O(l) ↔ H+
(aq)+ OH-
(aq)
Shift toward
reactants
Energetically
unfavourable
Non spontaneous
Mixture
reactant/productEquilibrium
veG  Spontaneous Shift toward
product
79G
33G
6
10G
14
101 
cK
5
105cK
Fe(s) + 3O2(g) ↔ 2Fe2O3(s) 261
101cK
Shift toward
reactants
Energetically
unfavourable
Shift toward
product
Energetically
favourable
Energetically
favourable
Kinetically unfavourable/(stable)
Rate too slow due to HIGH activation energy
Rusting Process
Energy barrier
Shift toward
product
Click here for notes
cellnFEG  
Cell Potential
cellE
0cellE
0cellE
0cellE
0cellE
0cellE
0cellE

15. Eθ
= +0.44V
IB Questions
Esterification produce ethyl ethanoate. ΔG = -4.38kJmol-1 Cal Kc
CH3COOH(l) + C2H5OH(l) ↔ CH3COOC2H5(l) + H2O(l)
Kc = 5.9
cKRTG ln
RT
G
Kc

ln
29831.8
4380
ln


cK
2
?cK
NO oxidized to NO2. Kc = 1.7 x 1012. Cal ∆G at 298K1
3 4
2NO+ O2 ↔ NO2 ?G
cKRTG ln
11
12
7.6969772
)107.1ln(298314.8



kJmolJmolG
G
Predict if iron react with HCI in absence air. Cal E cell , ∆G and Kc
Oxidized sp ↔ Reduced sp Eθ/V
Fe2+ + 2e- ↔ Fe -0.44
2H+ + 2e- ↔ H2 0.00
O2 +2H2O+4e ↔ 4OH- +0.40
Fe2+ + 2e- ↔ Fe -0.44
2H+ + 2e- ↔ H2 0.00
О
О
Fe ↔ Fe2+ + 2e Eθ = +0.44
2H+ + 2e ↔ H2 Eθ = 0.00V
Fe + 2H+ → Fe2+ + H2 Eθ = +0.44V
cellnFEG  
kJJG
G
8584900
44.0965002




cKRTG ln 
298314.8
)85000(
ln





RT
G
Kc
14
108.7 cK
∆G –ve, E +ve, K > 1
∆G <0, E > 0, K > 1
↓
Rxn Spontaneous
Fe2+ + 2e- ↔ Fe -0.44
O2 +2H2O+4e ↔ 4OH- +0.40
2Fe ↔ 2Fe2+ + 4e Eθ = +0.44
O2+2H2O+4e↔ 4OH- Eθ = +0.40
2Fe+O2 +2H2O→2Fe2++4OH- Eθ = +0.84V
Eθ
= +0.84V
Oxidized sp ↔ Reduced sp Eθ/V
Fe2+ + 2e- ↔ Fe -0.44
2H+ + 2e- ↔ H2 0.00
O2 +2H2O+4e ↔ 4OH- +0.40
Predict iron react HCI in presence of air. Cal E cell , ∆G and Kc
О
О
cellnFEG  
kJJG
G
324324000
84.0965004




cKRTG ln 
298314.8
)324000(
ln





RT
G
Kc
56
108.2 cK
∆G –ve, E +ve, K > 1
∆G <0, E > 0, K > 1
↓
Rxn SpontaneousRusting is spontaneous
x 2
О
О
О
О

16. Predict if manganate will oxidize chloride ion?
MnO2 + 4H+ + 2CI- → Mn2+ + 2H2O + CI2
5
MnO2 +4H+ + 2e- ↔ Mn2+ + 2H2O +1.23
1/2CI2 + e- ↔ CI- +1.36
2CI- ↔ CI2 + 2e Eθ = -1.36
MnO2 + 4H+ + 2e ↔ Mn2+ + 2H2O Eθ = +1.23
MnO2 + 4H++2CI- → Mn2++2H2O+CI2 Eθ= -0.13V
Eθ
= -0.13V
Oxidized sp ↔ Reduced sp Eθ/V
Cr2O7
2-+ 14H+ + 6e- ↔ 2Cr3+ + 7H2O +1.33
MnO2 +4H+ + 2e- ↔ Mn2+ + 2H2O +1.23
1/2CI2 + e- ↔ CI- +1.36
MnO4
-
+ 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51
Predict if MnO4
- able to oxidize aq CI- to CI2
2MnO4 + 16H+ + 10CI- → 2Mn2++ 8H2O + 5CI2
О
О
Oxidized sp ↔ Reduced sp Eθ/V
Cr2O7
2-+ 14H+ + 6e- ↔ 2Cr3+ + 7H2O +1.33
MnO2 +4H+ + 2e- ↔ Mn2+ + 2H2O +1.23
1/2CI2 + e- ↔ CI- +1.36
MnO4
-
+ 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51
О
О
2CI- ↔ CI2 + 2e Eθ = -1.36
MnO4
- + 8H+ + 5e ↔ Mn2+ + 4H2O Eθ = +1.51
2MnO4 + 16H++10CI- → 2Mn2++8H2O+5CI2 Eθ= +0.15V
1/2CI2 + e- ↔ CI- +1.36
MnO4
-
+ 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51
Eθ
= +0.15V
IB Questions
cellnFEG  
kJJG
G
2525000
13.0965002




cKRTG ln 
298314.8
)25000(
ln





RT
G
Kc
5
105.4 
cK
∆G +ve, E -ve, K < 1
∆G >0, E < 0, K < 1
↓
Rxn Non Spontaneous
6
cellnFEG  
kJJG
G
144144750
15.09650010




cKRTG ln 
298314.8
)144000(
ln





RT
G
Kc
25
105.1 cK
∆G –ve, E +ve, K > 1
∆G <0, E > 0, K > 1
↓
Rxn Spontaneous
x 5
x 2
О
О
О
О