ib chemistry on gibbs free energy, equilibrium constant and cell potential
TRANSCRIPT
cellnFEG
Relationship between Energetics and Equilibrium
cKRTG ln STHG
Enthalpy
change
Entropy
change
Equilibrium
constant
Gibbs free
energy change
HG
Relationship bet ∆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
cKK
nF
RTE cell ln
Magnitude of Kc Extend of reaction
How far rxn shift to right or left?
Not how fast
cK
Position of 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
HG 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
Magnitude of Kc Extend of reaction
How far rxn shift to right or left?
Not how fast
cK
Position of 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
HG 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
Relationship bet ∆G and Kc
GEnergetically
Thermodynamically Favourable/feasible
Sign predict spontaneity of rxn
veG veG
NOT favourable
Energetically favourable
Product formation NO product
KRTG ln
Predict will 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
1cK 1cK
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
GEnergetically
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
1cK 1cK
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% B 30 % 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
Predict will rxn occur with ΔG and Kc
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 > 1 Equilibrium mix close to product
10 % A 90 % B
∆G < 0
∆G < 0 ∆G = 0
∆G very –ve → Kc > 1 → (more product/close to 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 < 1 100% 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
product product
product product
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 > 1 Equilibrium mixture
10 % A 90 % B
∆G < 0
∆G < 0 ∆G = 0
∆G very –ve → Kc > 1 → (All product/close to 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
298314.8
)212000(ln
RT
GK c
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
Eθcell = Eθ
(cathode) – Eθ (anode)
Eθcell = +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 Eθcell (use reduction potential) Find Eθ
cell (use formula)
Eθcell = 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 Spontaneous cKRTG ln
Equilibrium
constant Gas constant, 8.314
∆G with Kc
cKRTG ln 37103.1 cK
Favour products
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
Eθcell = Eθ
(cathode) – Eθ (anode)
Eθcell = +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 Eθcell (use reduction potential) Find Eθ
cell (use formula)
Eθcell = 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
GK c
52105.3 cK
∆G –ve, E +ve, K > 1 ∆G <0, E > 0, K > 1
↓ Rxn Spontaneous
Favour products
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
Eθcell = Eθ
(cathode) – Eθ (anode)
Eθcell = -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 Eθcell (use reduction potential) Find Eθ
cell (use formula)
Eθcell = 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+
-
-
-
-
Ni Mn
+
+
+
+ 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
GK c
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
31102.2 cK
Favour products
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 Eθcell (use formula)
Eθcell = Eθ
(cathode) – Eθ (anode)
Eθcell = 0.00 – (+0.34) = -0.34V
Eθ = -0.34V (NON spontaneous)
О
Rxn not feasible
Determine spontaneity rxn. Will it HAPPEN ?
Find Eθcell (use reduction potential)
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
GK c
∆G +ve, E -ve, K < 1 ∆G >0, E < 0, K < 1
↓ Rxn Non Spontaneous
12104 cK
Favour reactants
-0.34 V
acid
copper
Predicting will rxn occur with ΔG, E cell and Kc
+
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 Eθcell (use formula)
Eθcell = Eθ
(cathode) – Eθ (anode)
Eθcell = 0.00 – (+1.58) = -1.58V
Eθ = - 1.58 V (NON spontaneous)
О
Rxn not feasible
Determine spontaneity rxn. Will it HAPPEN ?
Find Eθcell (use reduction potential)
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
GK c
∆G +ve, E -ve, K < 1 ∆G >0, E < 0, K < 1
↓ Rxn Non Spontaneous
50104 cK
Kc too small – No reaction at all
-1.58 V
acid
gold
2Au ↔ 2Au3+ + 6e Eθ = -1.58 6H+ + 6e ↔ 3H2 E
θ = 0.00 2Au + 6H+ → 2Au3+ + 3H2
Eθ = -1.58V +
Predicting will rxn occur with ΔG, E cell and Kc
Eθ = - 0.20 V (NON spontaneous)
(Oxidation) (Reduction)
Anode Cathode
Find Eθcell (use formula)
Eθcell = Eθ
(cathode) – Eθ (anode)
Eθcell = 0.34 – (0.54) = - 0.20V
Eθ = - 0.20 V (NON spontaneous)
Determine spontaneity rxn. Will it HAPPEN ?
Find Eθcell (use reduction potential)
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
GK c
∆G +ve, E -ve, K < 1 ∆G >0, E < 0, K < 1
↓ Rxn Non Spontaneous
7102.2 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 Cu 2+ to Cu
Predicting will rxn occur with ΔG, E cell and Kc
Click here to view free energy
Predicting Spontaneity of Rxn
Thermodynamic, ΔG Equilibrium, Kc
1cK
1cK
KRTG lnG
veG
cK
1cK
Energetically favourable
0G
Predicting rxn will occur?
N2(g) + 3H2(g) ↔ 2NH3(g)
H2O(l) ↔ H+(aq)+ OH-
(aq)
Shift toward reactants
Energetically unfavourable
Non spontaneous
Mixture reactant/product Equilibrium
veG Spontaneous Shift toward product
79G
33G
610G
14101 cK
5105cK
Fe(s) + 3O2(g) ↔ 2Fe2O3(s) 261101cK
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
0cellE
0cellE
0cellE
0cellE
0cellE
0cellE
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 lnRT
GK c
ln
29831.8
4380ln
cK
2
?cK
NO oxidized to NO2. Kc = 1.7 x 1012. Cal ∆G at 298K 1
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 E
θ = 0.00V Fe + 2H+ → Fe2+ + H2
Eθ = +0.44V
cellnFEG
kJJG
G
8584900
44.0965002
cKRTG ln
298314.8
)85000(ln
RT
GK c
14108.7 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
GK c
56108.2 cK
∆G –ve, E +ve, K > 1 ∆G <0, E > 0, K > 1
↓ Rxn Spontaneous Rusting is spontaneous
x 2
О О
О О
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 E
θ= -0.13V
Eθ = -0.13V
Oxidized sp ↔ Reduced sp Eθ/V
Cr2O72-+ 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
Cr2O72-+ 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 E
θ= +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
GK c
5105.4 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
GK c
25105.1 cK
∆G –ve, E +ve, K > 1 ∆G <0, E > 0, K > 1
↓ Rxn Spontaneous
x 5 x 2
О
О
О
О