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

http://lawrencekok.blogspot.com

Prepared by Lawrence Kok

Tutorial on Gibbs Free Energy Change, Equilibrium and Cell Potential

http://lawrencekok.blogspot.com/

cellnFEG

Relationship betweenEnergetics 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 betweenEnergetics and Cell Potential

G cellE


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 ReactionNon spontaneous

ΔGθ = 0 Kc = 1

0 EquilibriumMix

reactant/product

< 0 > 1 > 0 Reaction completeSpontaneous

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

∆G θ = -nFE θ cell ∆Gθ = -R

T ln K c

KnFRTE cell ln

Magnitude of Kc

Extend of reaction

How far rxn shift to right or left?

Not how fast

cK

Position of equilibrium

cKTemp

dependentExtend of rxn

Not how fast

Shift to left/favour

reactant

Shift to right/favour

product

cKRelationship between

Equilibrium and Energetics

cKRTG ln STHG

Enthalpy change

Entropy change



HG cK

GEnergetically

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

cKTemp

dependentExtend of rxn

Not how fast


reactant

Shift to right/favour

product

cKRelationship between

Equilibrium and Energetics

cKRTG ln STHG

Enthalpy change

Entropy 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

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


reactant

Very BIG Kc > 1 veG veG

KRTG ln

1cK 1cK

Negative (-ve)spontaneous



ΔGθ Kc Eq mixture

ΔGθ = + 200

9 x 10-

36Reactant






shift to right (product)

G, Gibbs free energy

A

Mixture composition

B

100% A 100% B

∆G decreases ↓

30 % A70 % 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 = 0System seek lowest possible free energy

Product have lower free energy than reactant

∆G < 0 productreactant

GEnergetically

Thermodynamically

Favourable/feasible


veG veG

NOT

favourable

Energetically

favourable

Product formation

NO product

KRTG ln

cK

Very SMALL Kc < 1

Shift to right/favour product


reactant

Very BIG Kc > 1 veG veG

KRTG ln

1cK 1cK

Negative (-ve)spontaneous


Relationship bet ∆G, Q and Kc


A

B

100% A 100% B

∆G decreases ↓

30 % A70 % B

Equilibrium mixture

∆G < 0


Free energy minimum

∆G < 0∆G < 0

∆G = 0

∆G < 0 productreactant


reactant product∆G < 0A

B

∆G decreases ↓

100% A 100% B30 % A70 % 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 % A70 % B

Equilibrium mix close to product

∆G < 0


Free energy minimum

∆G < 0∆G < 0

∆G = 0

∆G < -10

Kc > 1

A ↔ B A ↔ BG, Gibbs free energy

A

B

∆G decreases ↓

∆G < -100

100% A

100% B


Free energy minimum

Kc > 1Equilibrium mix close to product

10 % A90 % 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 ↔ BG, Gibbs free energy

100% A

100% B

A

B

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

∆G > +10


Free energy minimum

Kc < 1

∆G increases ↑

70 % A30 % B

Equilibrium mix close to reactant

∆G < 0∆G = 0

A ↔ BG, Gibbs free energy

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

A


Free energy minimum

Kc < 1100% A

100% B

Equilibrium mix close to reactant/ No reaction.

∆G > +100B

90 % A10 % B

∆G increases ↑

∆G = 0∆G < 0

reactant

reactant

reactant

reactant

productproduct

product product



shift to right (product)


A

B

100% A

100% B

∆G decreases ↓

30 % A70 % 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 = 0System seek lowest possible free energy

Product have lower free energy than reactant

∆G < -10

Kc > 1

A ↔ B A ↔ BG, Gibbs free energy

A

B

∆G decreases ↓

∆G < -100

100% A

100% B


Free energy minimum

Kc > 1Equilibrium mixture

10 % A90 % 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 reactantsKc <1

Complete rxn/Most productsKc > 1

Kc = 1 (Equilibrium)Reactants = Products

reactant reactant

ΔGθ Kc Eq mixture

ΔGθ = + 200

9 x 10-36 Reactant





298314.8)212000(ln

RTGK c

Zn ↔ Zn2+ + 2e Eθ = +0.76Cu2+ + 2e ↔ Cu Eθ = +0.34Zn + 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 = -0.76VCu2+ + 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 = -0.76VCu2+ + 2e ↔ Cu Eθ = +0.34V

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- ↔ Li -3.04K+ + e- ↔ K -2.93Ca2+ + 2e- ↔ Ca -2.87Na+ + e- ↔ Na -2.71Mg 2+ + 2e- ↔ Mg -2.37Al3+ + 3e- ↔ AI -1.66Mn2+ + 2e- ↔ Mn -1.19H2O + e- ↔ 1/2H2 + OH- -0.83Zn2+ + 2e- ↔ Zn - 0.76Fe2+ + 2e- ↔ Fe -0.45Ni2+ + 2e- ↔ Ni -0.26Sn2+ + 2e- ↔ Sn -0.14Pb2+ + 2e- ↔ Pb -0.13H+ + e- ↔ 1/2H2 0.00Cu2+ + e- ↔ Cu+ +0.15SO4

2- + 4H+ + 2e- ↔ H2SO3 +0.17Cu2+ + 2e- ↔ Cu + 0.341/2O2 + 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


Gas constant, 8.314

∆G with Kc

cKRTG ln 37103.1 cKFavour products

Zn ↔ Zn2+ + 2e Eθ = +0.762Ag++2e ↔ 2Ag Eθ = +0.80Zn + 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



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 = -0.76VAg + + e ↔ Ag(cathode) Eθ = +0.80V



cell (use formula)

Eθcell = Eθ


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

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- ↔ Li -3.04K+ + e- ↔ K -2.93Ca2+ + 2e- ↔ Ca -2.87Na+ + e- ↔ Na -2.71Mg 2+ + 2e- ↔ Mg -2.37Al3+ + 3e- ↔ AI -1.66Mn2+ + 2e- ↔ Mn -1.19H2O + e- ↔ 1/2H2 + OH- -0.83Zn2+ + 2e- ↔ Zn - 0.76Fe2+ + 2e- ↔ Fe -0.45Ni2+ + 2e- ↔ Ni -0.26Sn2+ + 2e- ↔ Sn -0.14Pb2+ + 2e- ↔ Pb -0.13H+ + e- ↔ 1/2H2 0.00Cu2+ + e- ↔ Cu+ +0.15SO4

2- + 4H+ + 2e- ↔ H2SO3 +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40Cu+ + e- ↔ Cu +0.521/2I2 + e- ↔ I- +0.54Fe3+ + e- ↔ Fe2+ +0.77Ag+ + e- ↔ Ag + 0.801/2Br2 + 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

RTGK c

52105.3 cK

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

↓Rxn Spontaneous

Favour products

Mn ↔ Mn2+ + 2e Eθ = +1.19Ni2+ + 2e ↔ Ni Eθ = -0.26Mn + 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



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 = -1.19VNi2+ + 2e ↔ Ni Eθ = -0.26V

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- ↔ Li -3.04K+ + e- ↔ K -2.93Ca2+ + 2e- ↔ Ca -2.87Na+ + e- ↔ Na -2.71Mg 2+ + 2e- ↔ Mg -2.37Al3+ + 3e- ↔ AI -1.66Mn2+ + 2e- ↔ Mn -1.19H2O + e- ↔ 1/2H2 -0.83Zn2+ + 2e- ↔ Zn -0.76Fe2+ + 2e- ↔ Fe -0.45Ni2+ + 2e- ↔ Ni - 0.26Sn2+ + 2e- ↔ Sn -0.14Pb2+ + 2e- ↔ Pb -0.13H+ + e- ↔ 1/2H2 0.00Cu2+ + e- ↔ Cu+ +0.15SO4

2- + 4H+ + 2e- ↔ H2SO3 + H2O +0.17Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40Cu+ + e- ↔ Cu +0.521/2I2 + e- ↔ I- +0.54+

+0.93 V

Eθ Mn/Ni = +0.93V

Ni2+

----

NiMn++++Mn2+

E cell with ∆G

cellnFEG


cellnFEG

kJJG

G

179179490

93.0965002

cKRTG ln

298314.8)179000(ln

RTGK c

cKRTG ln

∆G with Kc


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

↓Rxn Spontaneous

31102.2 cKFavour products

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- ↔ Li -3.04K+ + e- ↔ K -2.93Ca2+ + 2e- ↔ Ca -2.87Na+ + e- ↔ Na -2.71Mg 2+ + 2e- ↔ Mg -2.37Al3+ + 3e- ↔ AI -1.66Mn2+ + 2e- ↔ Mn -1.19H2O + e- ↔ H2 + OH- -0.83Zn2+ + 2e- ↔ Zn -0.76Fe2+ + 2e- ↔ Fe -0.45Ni2+ + 2e- ↔ Ni -0.26Sn2+ + 2e- ↔ Sn -0.14

H+ + e- ↔ H2 0.00Cu2+ + e- ↔ Cu+ +0.15SO4

2- + 4H+ + 2e- ↔ H2S +0.17Cu2+ + 2e- ↔ Cu +0.34

Cu ↔ Cu2+ + 2e Eθ = -0.342H+ + 2e ↔ H2 Eθ = +0.00Cu + 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


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+ = - 0.34VE cell with ∆G

cellnFEG


cellnFEG

kJJG

G

6565620

34.0965002

cKRTG ln


∆G with Kc

cKRTG ln

298314.8)65000(ln

RTGK c

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

↓Rxn Non Spontaneous

12104 cKFavour reactants

-0.34 V

acid

copper

Predicting will rxn occur with ΔG, E cell and Kc

+

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- ↔ Li -3.04K+ + e- ↔ K -2.93Ca2+ + 2e- ↔ Ca -2.87Na+ + e- ↔ Na -2.71Mg 2+ + 2e- ↔ Mg -2.37Al3+ + 3e- ↔ AI -1.66Mn2+ + 2e- ↔ Mn -1.19H2O + e- ↔ H2 + OH- -0.83Zn2+ + 2e- ↔ Zn -0.76Fe2+ + 2e- ↔ Fe -0.45Ni2+ + 2e- ↔ Ni -0.26Sn2+ + 2e- ↔ Sn -0.14

H+ + e- ↔ H2 0.00Cu2+ + e- ↔ Cu+ +0.15SO4

2- + 4H+ + 2e- ↔ H2S +0.17Cu2+ + 2e- ↔ Cu +0.34

Au3+ + 3e- ↔ Au +1.58

Rxn bet Au + H+

Will it happen ?

Eθ = -1.58 V (NON spontaneous)

ОAu(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+ = - 1.58VE cell with ∆G

cellnFEG


cellnFEG

kJJG

G

914914820

58.1965006

cKRTG ln


∆G with Kc

cKRTG ln

298314.8)914000(ln

RTGK c

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


50104 cKKc too small – No reaction at all

-1.58 V

acid

gold

2Au ↔ 2Au3+ + 6e Eθ = -1.586H+ + 6e ↔ 3H2 Eθ = 0.002Au + 6H+ → 2Au3+ + 3H2

Eθ

= -1.58V


+



Anode Cathode


Eθcell = Eθ


Eθcell = 0.34 – (0.54) = - 0.20V




Eθ Cu2+/I- = - 0.20VE cell with ∆G

cellnFEG


cellnFEG

kJJG

G

3838600

20.0965002

cKRTG ln


∆G with Kc

cKRTG ln

298314.8)38000(ln

RTGK 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 = -0.54Cu2+ + 2e ↔ Cu Eθ = +0.342I- + Cu2+→ Cu + I2

Eθ = -0.20V

Pt(s) | I-, I2 || Cu2+(aq) | Cu (s)

Favour reactants

Oxidized sp ↔ Reduced sp Eθ/VLi+ + e- ↔ Li -3.04K+ + e- ↔ K -2.93Ca2+ + 2e- ↔ Ca -2.87Na+ + e- ↔ Na -2.71Mg 2+ + 2e- ↔ Mg -2.37Al3+ + 3e- ↔ AI -1.66Mn2+ + 2e- ↔ Mn -1.19Zn2+ + 2e- ↔ Zn -0.76Fe2+ + 2e- ↔ Fe -0.45Ni2+ + 2e- ↔ Ni -0.26Sn2+ + 2e- ↔ Sn -0.14H+ + e- ↔ 1/2H2 0.00Cu2+ + e- ↔ Cu+ +0.15

Cu2+ + 2e- ↔ Cu +0.341/2O2 + H2O +2e- ↔ 2OH- +0.40Cu+ + e- ↔ Cu +0.52I2 + 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

Energeticallyunfavourable Non spontaneous

Mixturereactant/productEquilibrium

veG Spontaneous Shift toward product

79G

33G610G

14101 cK

5105cK

Fe(s) + 3O2(g) ↔ 2Fe2O3(s)

261101cK

Shift toward reactants

Energeticallyunfavourable

Shift toward product



Kinetically unfavourable/(stable)Rate too slow due to HIGH activation energy

Rusting Process

Energy barrier

Shift toward product

Reaction too slow

Click here for notes

cellnFEG

Cell Potential

cellE

0cellE

0cellE

0cellE

0cellE

0cellE

0cellE

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

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

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

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 lnRTGK c

ln

29831.84380ln

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/VFe2+ + 2e- ↔ Fe -0.442H+ + 2e- ↔ H2 0.00O2 +2H2O+4e ↔ 4OH- +0.40

Fe2+ + 2e- ↔ Fe -0.442H+ + 2e- ↔ H2 0.00

ОО

Fe ↔ Fe2+ + 2e Eθ = +0.442H+ + 2e ↔ H2 Eθ = 0.00VFe + 2H+ → Fe2+ + H2

Eθ = +0.44V

cellnFEG

kJJG

G

8584900

44.0965002

cKRTG ln

298314.8)85000(ln

RTGK c

14108.7 cK

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

↓Rxn Spontaneous

Fe2+ + 2e- ↔ Fe -0.44O2 +2H2O+4e ↔ 4OH- +0.40

2Fe ↔ 2Fe2+ + 4e Eθ = +0.44O2+2H2O+4e ↔ 4OH- Eθ = +0.402Fe +O2

+2H2O→2Fe2++4OH- Eθ = +0.84V

Eθ = +0.84V

Oxidized sp ↔ Reduced sp Eθ/VFe2+ + 2e- ↔ Fe -0.442H+ + 2e- ↔ H2 0.00O2 +2H2O+4e ↔ 4OH- +0.40

Predict iron react HCI in presence of air. Cal E cell , ∆G and KcО

О cellnFEG

kJJG

G

324324000

84.0965004

cKRTG ln

298314.8)324000(ln

RTGK c

56108.2 cK

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

↓Rxn SpontaneousRusting is spontaneous

x 2

ОО ОО

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 = -1.36MnO2 + 4H+ + 2e ↔ Mn2+ + 2H2O Eθ = +1.23MnO2 + 4H++2CI- → Mn2++2H2O+CI2

Eθ= -0.13V Eθ = -0.13V

Oxidized sp ↔ Reduced sp Eθ/VCr2O7

2-+ 14H+ + 6e- ↔ 2Cr3+ + 7H2O +1.33MnO2

+4H+ + 2e- ↔ Mn2+ + 2H2O +1.231/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

Predict if MnO4- able to oxidize aq CI- to CI2

2MnO4 + 16H+ + 10CI- → 2Mn2+ + 8H2O + 5CI2

ОО Oxidized sp ↔ Reduced sp Eθ/VCr2O7

2-+ 14H+ + 6e- ↔ 2Cr3+ + 7H2O +1.33MnO2

+4H+ + 2e- ↔ Mn2+ + 2H2O +1.231/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

О О2CI- ↔ CI2 + 2e Eθ = -1.36MnO4 - + 8H+ + 5e ↔ Mn2+ + 4H2O Eθ = +1.512MnO4 + 16H++10CI- → 2Mn2++8H2O+5CI2 Eθ= +0.15V

1/2CI2 + e- ↔ CI- +1.36MnO4

- + 8H+ + 5e- ↔ Mn2+ + 4H2O +1.51

Eθ = +0.15V

IB Questions

cellnFEG

kJJG

G

2525000

13.0965002

cKRTG ln

298314.8)25000(ln

RTGK 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

RTGK c

25105.1 cK

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

↓Rxn Spontaneous

x 5x 2

О О О О

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/

Prepared by Lawrence Kok

Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com

http://creativecommons.org/licenses/



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

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