ElectrochemistryElectrochemistry is a very diverse area. It can be broadly divided into a) analytical electrochemistry which is concerned with methods of measurement involving
potentiometry (pH meters etc), voltammetry, and modern sensors (generally voltammetricin nature)
b) physical electrochemistry is the basis of analytical electrochemistry, but is generallyconcerned with the effect of electric fields, charge balance, and diffusion.
c) Chemical electrochemistry usually is less interested in quantitative analysis but is devotedto understanding the mechanisms of electron transfer based on chemical structure.
d) Biologic electrochemistry can be understood as a form of physical electrochemistry(charge and fields around biomolecules) and of chemical electrochemistry (electron transferevents in biological systems)
e) Geologic and environmental electrochemistry is concerned with all of the above as theytake place in the natural environment . Of particular interest are the oxidation reductionreactions of iron, manganese, chromium, arsenic, sulfur, as these set the parameters inwhich life can grow and, as the oxidation state of iron has substantial implications for thestability of various minerals and their dissolution/formation.
f) Technical - in this field fall the major areas of batteries, solar energy, fuel cells, andcorrosion sciences.
ElectrochemistryFundamental concepts
Electron flow, nomenclatureEnergy in the electron flowKinetics of the electron transfer event as
influenced by a) energy b) homogeneous vs heterogeneous system
Electrochemistry
Energy :1. Heat out/Heat in = enthalpy, H2. Equilibrium Constants, K3. Universal Entropy ~ Free energy, G
Use total free energy – not just enthalpy
This reaction is exothermic.How much?
8 5 5 442 2 3
2H M nO F e M n F e H Oaq aq aq aq aq
,
species Hfo (kJ/mol)
8H+(aq) 0
4H2O(liquid) -286MnO4
-(aq) -543
Mn2+(aq) -218.8
5Fe2+(aq) -47.69
5Fe3+(aq) -87.86
H n H n Hrxo
i p roducts f i p roductso
i reac ts f i reac tso , , , , tan , , tan
H rxo
1 2 1 8 8 5 8 7 8 6 4 2 8 6
8 0 1 5 4 3 5 4 7 6 9
. .
.
H rxo 2 1 2 6 7 8 1 4 5.
H kJrxo 1 3 4 4
This reaction could do a lot of work for us if we could get the energy
MnO4-Fe2+
H kJrxo 1 3 4 4
8 5 5 424
2 32H F e M nO M n F e H Oaq aq aq aq aq
,
Heat water to convert energy?
Water Bath
Water circulation
inefficientclumsyheat loss
steam drive pistons
Make electricity
MnO4-Fe2+
Alternative Strategy: Capture electrons directly
MnO4-Fe2+
eMn2+
Fe3+
Split into 2 partial reactions
To do thisNeed to balanceRedox reactions
Writing the Net Ionic Reaction of an Oxidation-Reduction Reaction
Write oxidation half reaction Write reduction half reaction
Split into Reactions to be balanced
A. Balance atoms of element oxidizedb. Balance Rx sides by adding ec. Balance charge by adding H+
or OH-
d. Balance hydrogen by adding H2Oe. Balance oxygen
A. Balance atoms of element reducedb. Balance Rx sides by adding ec. Balance charge by adding H+
or OH-
d. Balance hydrogen by adding H2O
e. Balance oxygen
Combine and balance electrons
Writing the Net Ionic Reaction of an Oxidation-Reduction Reaction
Write oxidation half reaction Write reduction half reaction
Reaction to be balanced
A. Balance atoms of element oxidizedb. Balance Ox number with ec. Balance charge by adding H+
or OH-
d. Balance hydrogen by adding H2Oe. Balance oxygen
A. Balance atoms of element reducedb. Balance Ox number with ec. Balance charge by adding H+
or OH-
d. Balance hydrogen by adding H2O
e. Balance oxygen
Combine and balance electrons
Protons are addedin an acidic solutionand hydroxyls are added in a basic solution.
When in doubt add protons
Example: Balance the following redox equation in an acidic solution
F e M nO F e M naq aq aq aq( ) ( ) ( ) ( )2
43 2
F e F eaq aq( ) ( )2 3
F e F e eaq aq( ) ( )2 3
Mass balance
2+ 3+
Mass balance
-1 = 4(-2) +?8-1 = ? 7 = ?
+2
+7 +2
ox# balance
Ox #balance
M nO M naq aq42
( ) ( )
M nO e M naq aq425( ) ( )
Example: Balance the following redox equation in an acidic solution
F e M nO F e M naq aq aq aq( ) ( ) ( ) ( )2
43 2
F e F eaq aq( ) ( )2 3
F e F e eaq aq( ) ( )2 3
Mass balanced
2+ 3+
Mass balanced
Ox numbers
+7 +2
M nO e M naq aq425( ) ( )
M nO e H M naq aq aq425 8( ) ( )
Charge balance
+2-1 + -5 = -6
M nO M naq aq42
( ) ( )
Example: Balance the following redox equation in an acidic solution
F e M nO F e M naq aq aq aq( ) ( ) ( ) ( )2
43 2
F e F e eaq aq( ) ( )2 3 M nO e H M naq aq aq4
25 8( ) ( ) ( )
Balance hydrogen by adding water
M nO e H M n H Oaq aq aq42
25 8 4( ) ( ) ( )
Check oxygen balance
4O =4O
Check total charge balance: (-1)+5(-1)+8(+1)=+2
=+2
Example: Balance the following redox equation in an acidic solution
F e M nO F e M naq aq aq aq( ) ( ) ( ) ( )2
43 2
F e F e eaq aq( ) ( )2 3
M nO e H M n H Oaq aq aq42
25 8 4( ) ( ) ( )
Recombine while balancing electrons
5 5 52 3F e F e eaq aq( ) ( )
Example: Balance the following redox equation in an acidic solution
F e M nO F e M naq aq aq aq( ) ( ) ( ) ( )2
43 2
F e F e eaq aq( ) ( )2 3
M nO e H M n H Oaq aq aq42
25 8 4( ) ( ) ( )
5 5 52 3F e F e eaq aq( ) ( )
M nO F e H F e M n H Oaq aq aq aq aq42 3 2
25 8 5 4( ) ( ) ( ) ( ) ( )
Final equation does not show any electronsbecause electrons “do not exist” in solution
OJO: Important Point
The reactions
1. do not really occur by themselves2. they are linked through the electrons3. DEFINITION: = 1/2 reactions
M nO e H M n H Oaq aq aq42
25 8 4( ) ( ) ( )
5 5 52 3F e F e eaq aq( ) ( )
If all reactions are consideredHalf reactions where does the Electron go?
e nH O e aq 2
e nH O H H O k x M saq 3 2
1 0 1 12 3 1 0, .
e H O H H O k x M saq 2
1 1 11 9 1 0, .
Hydrated electrons not only react with waterBut with other species including biological,Hence it is a good way to sterilize water
e R SH H S R k x M saq , .1 1 1 0 1 0 1 1
e O O H O O H O k M saq
H O
pK H A
2 2
4 9
1 0 1 12
1 0.
, ~
Hydrated electrons in aerobic biology will produceFinite fluxes of the soft radical HOO
Not only have to consider rateBut energy
e nH O e E V vsN H Eaqo 2 3 0, .
e nH O H H O k x M s
E V vs N H E
aq
o
3 21 0 1 12 3 1 0
2 1 0
, .
, .
e H O H H O k x M s
E V vs N H E
aq
o
21 1 11 9 1 0
2 9 3 0
, .
, .H-O bondWater 464 kJHydronium 301 kJ
Some other practical considerations
1MnO4-
5Fe2+
eFe3+
e
Mn2+
M nO e H
M n H O
aq aq
aq
4
22
5 8
4
( ) ( )
( )
5 5 52 3F e F e eaq aq( ) ( )
--
--
-
--
--
-
Net charge=0
Net charge=0
Net charge=10(-1)+5(+3)=+5
Net charge = (+2)+2(+1)+(-1)=+3
+-
Do you think the Mn/Fe reaction will continue for long?
- anion+ cation
+
Will want to let spectator ions flow(but not the reactants!)
e
“jelly” (salt bridge) retards motion of Fe3+/2+ MnO4-
(current)
+15+
“jelly” allows motion of spectators which producesCharge balance
Fe3+
-
1. Always make electrons flow to right2. Electrons flow down to the cathode
(cat = Greek for down).3. Electrons flow up into the anode
(an = Greek for up)
Weird Grammar Rules: Those Italians!Volta discovered this process
Count Alessandro Volta, Italy~1800, first battery
e
Cl-
(current)
cathodeanode
oxidation reduction
Oxidationelectrons takenOut (up = anode)
Reductionelectrons acceptedIn (down = cathode)
AnAn oxAn ox jumped overAn ox jumped over a redAn ox jumped over a red cat
Rsb
Rsoln
There isResistanceIn the system,We will comeBack to this
Vocabulary for Work when usingelectrons instead of heat.
Ohm’s Law: Voltage = current x resistance
Voltage = energy required to move charge
= Joules/Coulomb
Georg Simon Ohm, 1789-1854German physicist having a good hair day
V IR
n m oles e F
C oulom b
m ole e
FV
Jou le
C ou lom bV
a coulomb is a unit of charge
F=Faraday = 96,485 coulombs of charge/mole of e
neg sign accounts for negative electron
n m oles e
nF V J nF V G
V directly relates to free energy because we are notSeparately the work terms into heat and changing surrounding randomness with the heat
OhmJouleCoulombNernst
n m oles e F n m oles e F
C oulom b
m ole e
F
n m oles e F
C oulom b
m ole e
FV
n m oles e F
C oulom b
m ole e
FV
Jou le
C oulom bV
J
Marie the Jewess, 300 Jabir ibn Hawan, 721-815
Galen, 170 Jean Picard1620-1682
Galileo Galili1564-1642
Daniel Fahrenheit1686-1737
Evangelista Torricelli1608-1647
Isaac Newton1643-1727
Robert Boyle, 1627-1691
Blaise Pascal1623-1662
Anders Celsius1701-1744
Charles Augustin Coulomb 1735-1806
John Dalton1766-1844
B. P. Emile Clapeyron1799-1864
Jacques Charles 1778-1850
Germain Henri Hess1802-1850
Fitch Rule G3: Science is Referential
William ThompsonLord Kelvin, 1824-1907
James Maxwell1831-1879
Johannes D.Van der Waals1837-1923
Justus von Liebig (1803-1873
Johann Balmer1825-1898
James Joule (1818-1889)
Johannes Rydberg1854-1919
Rudolph Clausius1822-1888
Thomas Graham1805-1869
Heinrich R. Hertz, 1857-1894
Max Planck1858-1947
J. J. Thomson1856-1940
Linus Pauling1901-1994
Werner Karl Heisenberg1901-1976
Wolfgang Pauli1900-1958
Count Alessandro GA A Volta, 1747-1827
Georg Simon Ohm 1789-1854
Henri Louis LeChatlier1850-1936
Svante Arrehenius1859-1927
Francois-Marie Raoult1830-1901
William Henry1775-1836
Gilbert N Lewis1875-1946
Fritz Haber1868-1934
Michael Faraday1791-1867
Luigi Galvani1737-1798
Walther Nernst1864-1941
Lawrence Henderson1878-1942
Amedeo Avogadro1756-1856
J. Willard Gibbs1839-1903
Niels Bohr1885-1962
Erwin Schodinger1887-1961
Louis de Broglie (1892-1987)
Friedrich H. Hund1896-1997
Fritz London1900-1954
An alchemist
Ludwig Boltzman1844-1906
Richard AC E Erlenmeyer1825-1909
Johannes Bronsted1879-1947
Thomas M Lowry1874-1936
James Watt1736-1819
Dmitri Mendeleev1834-1907
Marie Curie1867-1934
Henri Bequerel1852-1908
Rolf Sievert, 1896-1966
Louis Harold Gray1905-1965
Jacobus van’t Hoff1852-1911
For standard conditions (1 mole, 1 atm, 25C):
Greek GKomodo (Indonesia) KVamale (Polynesia) Vo
Different languages, same information. RepresentTotal energy (heat + entropy) associated with a reaction
nF V Go o nF V G R T Ko o ln
VR T
nFKo ln
Relationship G, K, V Example Problem 1 :What are K and the standard voltage associated with theFire oxidation of lead given tabulated free energies?
K eG
R T 0
K x 5 2 3 1 0 6 2.
2 22P b O P bOs g s ( )
G n G n Grxo
f products f reac tso , , tan
0
G kJrxo 3 5 7 8.
G m olP bOkJ
m olP bOm olP b
kJ
m olP bm olO
kJ
m olOrxo
s ss
21 8 7 9
20
10
22
.
K e
kJ
m ol
xkJ
m ol KK
3 5 7 8
8 3 1 4 1 0 2 9 83
.
.G R T Ko ln
Relationship G, K, V Example Problem 1 :What are K and the standard voltage associated with theFire oxidation of lead given tabulated free energies?
K x 5 2 3 1 0 6 2.
2 22P b O P bOs g s ( )
-nFV0 = Go
G kJrxo 3 5 7 8.
?
Ox # = 0
Compound neutralO usually -2So Pb = +22(+2)=4
+4
=-4electrons
Relationship G, K, V Example Problem 1 :What are K and the standard voltage associated with theFire oxidation of lead given tabulated free energies?
K x 5 2 3 1 0 6 2.
2 22P b O P bOs g s ( )
-nFV0 = Go
nF V G
VG
nF
kJ
m ol rx as w ritten
J
kJ
m ol elec trons
m ol reaction
cou lom bs
m ol elec tron
VJ
cou lom b
V
o o
oo
3 5 7 8
3 5 7 8 1 0 0 0
4 9 6 4 8 7
10 9 2
.
.
.
G kJrxo 3 5 7 8.
? n=4
K x 5 2 3 1 0 6 2.
2 22P b O P bOs g s ( )
V Vo 0 9 2.
G kJrxo 3 5 7 8. All tell us that reaction
Will spontaneously Proceed to the rightFavoring products
How will we conveniently store info?
Vo values for 1/2 reactionsCompared to protons
Reaction Vo
Cs+ + e Cs ?K+ + e K -2.95Na+ + e Na -2.71Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Br2 + 2e 2Br- 1.09Cl2
+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87
Observations, Please!!!!
1. What seems to be the “grammar” for the reactions?
2. What is the zero point?3. What do you expect the value for Cs to be?4. How do the values for the halogens compare
to the group I elements?5. Is there a trend in the halogens?6. How does this relate to the periodic chart?7. How does this relate to “charge density”?8. Who wants the electrons?9. Where are the guys that want the electrons
located on the chart?
We said that electrons are rapidlyAquated and, rapidly reactWhat about their energy?
e nH O e E V vsN H Eaqo 2 3 0, .
e nH O H H O k x M s
E V vs N H E
aq
o
3 21 0 1 12 3 1 0
2 1 0
, .
, .
e H O H H O k x M s
E V vs N H E
aq
o
21 1 11 9 1 0
2 9 3 0
, .
, .
H-O bondHydronium 301 kJWater 464 kJ
Reaction Vo
e + H2O eaq -3.0Cs+ + e Cs ?K+ + e K -2.95Na+ + e Na -2.71Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Br2 + 2e 2Br- 1.09Cl2
+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87want most
want least
have edon’t have e
Reaction Vo
Cs+ + e Cs ?K+ + e K -2.95Na+ + e Na -2.71Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Br2 + 2e 2Br- 1.09Cl2
+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87Don’t havewant most
Have ewant least
electronsflow down hillaway fromnegative voltage
Start arrow on right hand side and end on left hand
Think ofA watertower
Reaction Vo
Cs+ + e Cs ?K+ + e K -2.95Na+ + e Na -2.71Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Br2 + 2e 2Br- 1.09Cl2
+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87
Uphill reactions: not probableStart arrow on right hand side and end on left hand
Reaction Vo
Cs+ + e Cs ?K+ + e K -2.95Na+ + e Na -2.71Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Br2 + 2e 2Br- 1.09Cl2
+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87
Can I react F2 with K+?
Start arrow on right hand side and end on left hand
No, there is nobody to give away electrons,no electron source!
Reaction Vo
Cs+ + e Cs ?K+ + e K -2.95Na+ + e Na -2.71Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Br2 + 2e 2Br- 1.09Cl2
+ 2e 2Cl- 1.36F2 + 2e 2F- 2.87
Can I exchange e between Cs with Pb?
Start arrow on right hand side and end on left hand
There is nobody to accept electrons!
Which reactions will go?
a) Cs metal plus KBr?b) F2 gas plus PbCl2
c) Na metal plus chlorine gasd) Na+ + Cl-
Strategy:1. Pick one who has electrons2. Pick one who doesn’t 3. Draw an arrow, starting where the electron
is. 4. Is it up or downhill?
Example problem Standard V (good exam prototypes)
Reaction Vo
e + H2O eaq -3.0K+ + e K -2.95Na+ + e Na -2.71NCl3_4H+ + 6e 3Cl- + NH4
+ -1.37Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0N2(g) + 8H+ + 6e 2NH4
+ 0.275Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Ag+ + e Ag 0.799NO3
- + 4H+ + 3e NO(g) +2H2O 0.957Br2 + 2e 2Br- 1.092NO3
- + 12H+ + 10e N2(g) +6H2O 1.246Cl2
+ 2e 2Cl- 1.36Au+ + e Au 1.83F2 + 2e 2F- 2.87
Who rusts most?PbFeCuAgAu
Why?What do we use for plumbing?Why was gold considered the sacred material?
Reaction Vo
Fe2+ + 2e Fe -0.44Pb2+ + 2e Pb -0.132H+ + 2e H2(gas) 0Sn4++2e Sn2+ 0.154N2(g) + 8H+ + 6e 2NH4
+ 0.275Cu2+ + 2e Cu 0.34O2 + 2H2O + 4e 4OH- 0.40O2 + 2H+ + 2e H2O2 0.68Fe3
+ +e Fe2+ 0.769Hg2
2+ +2e 2Hg(l) 0.796Ag+ + e Ag 0.799NO3
- + 4H+ + 3e NO(g) +2H2O 0.957Br2 + 2e 2Br- 1.092NO3
- + 12H+ + 10e N2(g) +6H2O 1.246Cl2
+ 2e 2Cl- 1.36Au+ + e Au 1.83F2 + 2e 2F- 2.87
Sunday
Monday
Saturday
Tuesday
Wednesday
Friday
Thursday
M L M xL
M ne M
M L ne M xL
x aqueousn
aqueousn
aqueous
aqueousn
so lid
x aqueousn
so lid aqueous
,
,
Change in metalsequenceoccurs at timethat acids weredeveloped (1100-1400AD)(Islamic Chemists)
xM O M Oso lid
y
y so lid 2 2 2 ,
Chemical oxidation
V1/Kf
G
Air oxidation
~1300A.D
~100 B.C (Context Slide 1)
(Context Slide 2)
Some Rules1. Voltages sum2. Reversed reactions =change of sign3. Don’t worry about #electrons (n)
since V = Joule/coulomb of charge
Example Calculation: Summing V equationsWhat is the voltage for the reaction:
A e A V ao
A e B V a bo
/
2 A A B V ?
Given that
A A e V ao
A e B V a bo
/
2 A A B V V Va bo
ao
/
Example Summing V equations: If your lab partner attempts to add fluorine gas to a beaker containing potassium metal what should you do? Justify by calculating the reaction voltage and the free energy
Say your prayers and duck.
K e K V o 2 9 5.
F e F Vgo
2 2 2 2 8 7, .
2 2 2 2 9 5K e K V o .
2 2 2 2 9 5K K e V o
.
F e F Vgo
2 2 2 2 8 7, .
2 2 2 5 8 22K F K F V o
.
G nF Vo o
G o
2 2 9 5F . 2 2 8 7F .
2 5 8 2F .
2 9 6 4 8 1 0 5 8 24. .x 11 2 3kJ
How does concentration fit In?
G G R T Qo ln
nF V G G nF V o0
nF V nF V R T Qo ln
VnF V
nF
R T
nFQ
o
ln
V VR T
nFQo ln
V VR T
nF
C D
A Bo
c d
a b ln
Nernst Equation:
At 25 oC
V VR T
nF
C D
A Bo
c d
a b ln
V Vn
C D
A Bo
c d
a b 0 0 5 9 2.
lo g
When the reaction favors products, it isSpontaneous, or Galvanic
LuigiGalvani:
“Frog leg Guy”1780
M a Ca
M Ma a
More accurately:
lo g .
0 5 0 91
2zu
u
activity concentration
Activity coefficient
Ionic strength
u C Zi i 12
2
Marie the Jewess, 300 Jabir ibn Hawan, 721-815
Galen, 170 Jean Picard1620-1682
Galileo Galili1564-1642
Daniel Fahrenheit1686-1737
Evangelista Torricelli1608-1647
Isaac Newton1643-1727
Robert Boyle, 1627-1691
Blaise Pascal1623-1662
Anders Celsius1701-1744
Charles Augustin Coulomb 1735-1806
John Dalton1766-1844
B. P. Emile Clapeyron1799-1864
Jacques Charles 1778-1850
Germain Henri Hess1802-1850
Fitch Rule G3: Science is Referential
William ThompsonLord Kelvin, 1824-1907
James Maxwell1831-1879
Johannes D.Van der Waals1837-1923
Justus von Liebig (1803-1873
Johann Balmer1825-1898
James Joule (1818-1889)
Johannes Rydberg1854-1919
Rudolph Clausius1822-1888
Thomas Graham1805-1869
Heinrich R. Hertz, 1857-1894
Max Planck1858-1947
J. J. Thomson1856-1940
Linus Pauling1901-1994
Werner Karl Heisenberg1901-1976
Wolfgang Pauli1900-1958
Count Alessandro GA A Volta, 1747-1827
Georg Simon Ohm 1789-1854
Henri Louis LeChatlier1850-1936
Svante Arrehenius1859-1927
Francois-Marie Raoult1830-1901
William Henry1775-1836
Gilbert N Lewis1875-1946
Fritz Haber1868-1934
Michael Faraday1791-1867
Luigi Galvani1737-1798
Walther Nernst1864-1941
Lawrence Henderson1878-1942
Amedeo Avogadro1756-1856
J. Willard Gibbs1839-1903
Niels Bohr1885-1962
Erwin Schodinger1887-1961
Louis de Broglie (1892-1987)
Friedrich H. Hund1896-1997
Fritz London1900-1954
An alchemist
Ludwig Boltzman1844-1906
Richard AC E Erlenmeyer1825-1909
Johannes Bronsted1879-1947
Thomas M Lowry1874-1936
James Watt1736-1819
Dmitri Mendeleev1834-1907
Marie Curie1867-1934
Henri Bequerel1852-1908
Rolf Sievert, 1896-1966
Louis Harold Gray1905-1965
Jacobus van’t Hoff1852-1911
ElectrochemistryElectrochemistry is a very diverse area. It can be broadly divided into a) analytical electrochemistry which is concerned with methods of measurement involving
potentiometry (pH meters etc), voltammetry, and modern sensors (generally voltammetricin nature)
b) physical electrochemistry is the basis of analytical electrochemistry, but is generallyconcerned with the effect of electric fields, charge balance, and diffusion.
c) Chemical electrochemistry usually is less interested in quantitative analysis but is devotedto understanding the mechanisms of electron transfer based on chemical structure.
d) Biologic electrochemistry can be understood as a form of physical electrochemistry(charge and fields around biomolecules) and of chemical electrochemistry (electron transferevents in biological systems)
e) Geologic and environmental electrochemistry is concerned with all of the above as theytake place in the natural environment . Of particular interest are the oxidation reductionreactions of iron, manganese, chromium, arsenic, sulfur, as these set the parameters inwhich life can grow and, as the oxidation state of iron has substantial implications for thestability of various minerals and their dissolution/formation.
f) Technical - in this field fall the major areas of batteries, solar energy, fuel cells, andcorrosion sciences.
A preview……
Note the negativeTo positive Arrangement ofVoltages.
Electrons flow awayFrom the Negative sign.
Biological “Galvanic”(Spontaneous) Cell:Respiration
Note also verySmall voltage steps, 0.01 V is a large driver!
http://www.rpi.edu/dept/bcbp/molbiochem/MBWeb/mb1/part2/redox.htm
See also:Awesome site
CoQ = Coenzyme Q
Ubiquinone, Q
Ubiquinol, QH2
2e, 2H+
http://www.reciprocalnet.org/recipnet/showsample.jsp?sampleId=27344188&sampleHistoryId=13823
Open browser to see and rotate molecule
Q H e H Q V 2 2 0 6 9 9 92
0~ .
What is the role of the long tail?
BiologicalElectrochemistry
Cytochrome c oxidaseCytochrome C
FeContainingHeme group
8 2H Oin g , 4 H ou t
Membrane
Fe issquare planarwith 2 morecoordinationsites top and bottom.
One is used for oxygen transport
Hemeglobin:Oxygen carrier
http://www.elmhurst.edu/~chm/vchembook/568globularprotein.htmlReview: Module 18: Complex IonsReview: Module 17B: Acid Bases
Biological “Electrolytic” orNon-spontaneous cell:Photosynthesis
Electrons are “pumped” up towardsMore negative voltage
The pump chemistry is Similar (but not identical) to metal ligand crystalField splitting
light
700nm
680nm
Photosystems I and II
Electrochemistry in Mining
“In just a few years a large area of forest has been destroyed [near the Taxco silver mines], and it appears that the wood supply will be depleted sooner than the ore. Ordinances have been made regarding the conservation of the forest, and likewise regarding the paths that the Indian workers use for making charcoal, cutting wood, and on the maximum loads that may carry.”
The Conquest of Mexico
In 1550 the Viceroy wrote to the King
Requires a less fuelIntensive method
Mercury consumed in New World Spanish silver mines(1560-1820):170,000 tons; USA gold rush (1850-1900): 70,000 tons
(Context Slide 1)
Amalgamation was introduced in the 1550s in Mexico by a Spanish immigrant, Bartolome deMedina, who wrote Dec. 29, 1555 (1):
I, Bartolome de Medina do declare that I learned in Spain through discussion with aGerman, that silver can be extracted from ore without the necessity for smelting it, orrefining it, or incurring any other considerable expense. With this information Iresolved to come to New Spain. Leaving my home, my wife and my children in Spain, Icame to test it, knowing that if I were successful, I would render a great service to OurLord, and to his Majesty and to all this realm. And having spent much time and moneyand suffered mental anguish, and seeing that I was not going to be able to make itwork, I commended myself to Our Lady and I begged Her to enlighten me and guideme, so that I might be successful and it pleased Our Lady to enlighten me and put meon the right path so that I could make it work.
1. Probert, A. Bartolome de Medina: The Patio Process and the Sixteenth Century Silver Crisis. In M inesof Silver and Gold in the Americas.
Grind the ore fine. Steep it in strong brine. Add mercury and mix thoroughly. Repeatmixing daily for several weeks. Every day take a pinch of ore mud and examine themercury. See? It is bright and glistening. As times passes, it should darken as silverminerals are decomposed by salt and the silver forms an alloy with mercury. Amalgam is pasty. Wash out the spent ore in water. Retort residual amalgam;mercury is driven off and silver remains.
A description of the process 1555.
(Context Slide 2)
8 1 6 3 2 8 8 0 1 5 842
2 3 2 10SO e H H SO H O V .
8 1 6 8 4 1 2 0 4 0 02 3 2 32
2 2H SO e H S O H O V o . S S e Vs
o232 0 4 4 7 .
2 4 2 2 9 1 0 8 4 1 1 0 1 02 32
2 3 2
3 21 3 2 2 6 2 6 9A g S O A g S O K x xf
. . .
A g S A g S K sp22 5 12 1 0
A g S SO e H A g S O H O S s2 42
2 3 2
3
28 3 0 4 0 2 2 0
8 3 0 4 0 4 2 0 1 0 0 542
2 32
2SO e H S O H O S Vs neto .
lo g.
Kn
Vnet ne to
0 0 5 9 2
lo g.
. .K net 3 0
0 0 5 9 21 0 0 2 5 0 7 7
K vo ltage net,.1 0 5 0 7 7
K K K Kto ta l net f sp 2
5 0 7 7 2 6 9 5 0 1 4 8 4 51 0 1 0 1 0 1 0. . . .
Solubility
Complexation
ReductionOf S(how toGet the ligand)
(Context Slide 2)
insoluble
Could drive solubility
Couple Reactions Example• Most native silver has long since been used: 2. but we still mine silver dust.3. How is this economically feasible?4. How could we get rich with a new process involving CN
extraction?
A g C N O A g C Ns aq g aq
2 2, ,
What is the voltage, free energy, and K Associated with this reaction?
A g C N O A g C Ns aq g aq
2 2, ,
A g C N A g C Ns aq aq
2 ,
1. Balance the equationa. Split into ½ reactionsb. Balance each ½ reactionc. Recombine
A g C N A g C Ns aq aq
2 2 ,
A g C N A g C N es aq aq
2 12 ,
O g2 , ?
O H Og2 22,
O H H Og aq2 24 2,
O H e H Og aq2 24 4 2, 4 8 4 42A g C N A g C N es aq aq
,
4 8 4 42A g C N A g C N es aq aq
,
O H e H Og aq2 24 4 2,
4 8 4 4 22 2 2A g C N O H A g C N H Os aq g aq aq
, ,
V o 0 3 1.
V o 1 2 3.
V rxo 1 5 4.
The free energy for the reaction is a mere:
G = -nFVorx = -4(96485)(1.53) = -5.9x105 J
G = -RTln K
K = e(-G/RT) = e(-(-590000/(298x8.314)) = e238 = 10238/2.3
= 10103
all you need is:CN (cheap)O2 (air is cheap (an aerator))
Hypothetical Modern Silver/Gold Mine
Bulldozer
CN-
aerator
O2
Same process used to recover silver at photography studios, in silver plating.
Major cyanide spills: Czech, Elbe River, Jan. 2006; Romania, Tisza River, Nov. 2005; Laos, June, 2005; Ghana River Kubreko, Jan, 2005; China, Papua New Guinea, Ghana, Romania (10 tons Danube River, Mar. 2004), Ghana, Honduras, Nicaragua, China, 2002: Nevada, USA
Tibor Kocsis
(Context Slide)
Using Bugs to Mine Cu from CuS
8 82 3F e F ebugs
C u S F e H O F e C u SO Hs
22
2 32
2 2428 4 8 2 1 6
-14e
Catalytic reagent, supplied courtesy of bugs, Thiobacillus ferridoxin
collectKsp=10-36
Biomining forGold and Copper in Botswana
(Context Slide)
(Context Slide)
Coupled Chemical Equation Example Calculate the formal potential for the reaction to form the initial corrosion product, Fe(OH)3,s reaction at pH 7
2 2 4 0 4 42F e F e e V
.
O H O e O H V Oo
2 2 22 4 4 0 4 0
.
2 33 2 2 3F e O H H O F e Oslow( )
2 2 2 0 7 7 12 3F e F e e V
.12 2 2 22 2 0 4 0O H O e O H V O
o
.
F e O H F e O H K xsp3
33 83 6 3 1 0
( ) .
Introduction: Key Concepts
1. Grammer Rules: write all reactions as reductions
2. Half reactions3. Aquated electrons (carry electrons from
electrode to solution species) (disinfectants)4. Voltage is an energy term5. Applications
1. Disinfectants2. Biology3. Geology4. Industry
Top Related