ib chemistry on gibbs free energy, equilibrium constant and cell potential

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



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


GEnergetically

Thermodynamically Favourable/feasible


veG veG

NOT favourable



KRTG ln

Predict will rxn occur with ΔG and Kc

cK

Very SMALL Kc < 1



Very BIG Kc > 1

veG veG

KRTG ln

1cK 1cK




ΔGθ Kc Eq mixture

ΔGθ = + 200

9 x 10-36 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


veG veG

NOT favourable



KRTG ln

cK

Very SMALL Kc < 1



Very BIG Kc > 1

veG veG

KRTG ln

1cK 1cK



Relationship bet ∆G, Q and Kc


A

B

100% A 100% B

∆G decreases ↓

30 % A 70 % B

Equilibrium mixture

∆G < 0


Free energy minimum

∆G < 0

∆G < 0

∆G = 0

∆G < 0 product reactant


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



A

B

100% A

100% B

∆G decreases ↓

30 % A 70 % B

Equilibrium mix close to product

∆G < 0


Free energy minimum

∆G < 0

∆G < 0

∆G = 0

∆G < -10

Kc > 1

A ↔ B A ↔ B


A

B

∆G decreases ↓

∆G < -100

100% A

100% B


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


100% A

100% B

A

B

∆G +ve → Kc < 1 → (more reactant > product)

∆G > +10


Free energy minimum

Kc < 1

∆G increases ↑

70 % A 30 % B

Equilibrium mix close to reactant

∆G < 0

∆G = 0

A ↔ B


∆G more +ve → Kc < 1 → (All reactant / no product at all)

A


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



shift to right (product)


A

B

100% A

100% B

∆G decreases ↓

30 % A 70 % B

Equilibrium mixture

∆G < 0


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


A

B

∆G decreases ↓

∆G < -100

100% A

100% B


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





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


Salt Bridge Flow

electrons

Zn/Ag Voltaic Cell

-e -e

Zn/Ag half cells

Eθcell = Eθ


Eθcell = +0.80 – (-0.76) = +1.56V

Zn 2+ + 2e ↔ Zn (anode) Eθ = -0.76V Ag + + e ↔ Ag(cathode) Eθ = +0.80V



cell (use formula)

Eθcell = Eθ


Zn 2+ + 2e ↔ Zn Eθ = -0.76V Ag+ + e ↔ Ag Eθ = +0.80V


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


Salt Bridge Flow

electrons

Mn/Ni Voltaic Cell

-e -e

Mn/Ni half cells

Eθcell = Eθ


Eθcell = -0.26 – (-1.19) = +0.93V

Mn 2+ + 2e ↔ Mn (anode) Eθ = -1.19V Ni2+ + 2e ↔ Ni (cathode) Eθ = -0.26V



cell (use formula)

Eθcell = Eθ


Mn 2+ + 2e ↔ Mn Eθ = -1.19V Ni2+ + 2e ↔ Ni Eθ = -0.26V


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


cellnFEG

kJJG

G

179179490

93.0965002

cKRTG ln

298314.8

)179000(ln

RT

GK c

cKRTG ln

∆G with Kc


constant

∆G –ve, E +ve, K > 1 ∆G <0, E > 0, K > 1

↓ Rxn Spontaneous

31102.2 cK

Favour products


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)


Anode Cathode

Find Eθcell (use formula)

Eθcell = Eθ


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


cellnFEG

kJJG

G

6565620

34.0965002

cKRTG ln


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

+


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)


Anode Cathode


Eθcell = Eθ


Eθcell = 0.00 – (+1.58) = -1.58V

Eθ = - 1.58 V (NON spontaneous)

О

Rxn not feasible



Eθ Au/H+ = - 1.58V

E cell with ∆G

cellnFEG


cellnFEG

kJJG

G

914914820

58.1965006

cKRTG ln


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


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 +




Anode Cathode


Eθcell = Eθ


Eθcell = 0.34 – (0.54) = - 0.20V




Eθ Cu2+/I- = - 0.20V

E cell with ∆G

cellnFEG


cellnFEG

kJJG

G

3838600

20.0965002

cKRTG ln


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


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


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


Click here to view free energy

Predicting Spontaneity of Rxn

Thermodynamic, ΔG Equilibrium, Kc

1cK

1cK

KRTG lnG

veG

cK

1cK


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



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

https://www.youtube.com/watch?v=F1k8TJsVg_g

https://www.youtube.com/watch?v=F1k8TJsVg_g

http://depts.washington.edu/chemcrs/bulkdisk/chem152A_sum05/handout_Lecture_09_revised.pdf

http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/12._Chemical_Energetics/Free_Energy_and_Equilibrium

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


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


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


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


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


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

ib chemistry on gibbs free energy, equilibrium constant and cell potential

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