E at Nonstandard Conditions

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E at Nonstandard Conditions

• The NERNST EQUATION
• E potential under nonstandard conditions
• n no. of electrons exchanged
• ln natural log
• If P and R 1 mol/L, then E E
• If R gt P, then E is ______________ than E
• If R lt P, then E is ______________ than E

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BATTERIESPrimary, Secondary, and Fuel Cells
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Dry Cell Battery
Primary battery uses redox reactions that
cannot be restored by recharge.

• Anode (-)
• Zn ---gt Zn2 2e-
• Cathode ()
• 2 NH4 2e- ---gt 2 NH3 H2

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Alkaline Battery

• Nearly same reactions as in common dry cell, but
  under basic conditions.

Anode (-) Zn 2 OH- ---gt ZnO H2O
2e- Cathode () 2 MnO2 H2O 2e- ---gt
Mn2O3 2 OH-
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Lead Storage Battery

• Secondary battery
• Uses redox reactions that can be reversed.
• Can be restored by recharging

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Lead Storage Battery

• Anode (-) Eo 0.36 V
• Pb HSO4- ---gt PbSO4 H 2e-
• Cathode () Eo 1.68 V
• PbO2 HSO4- 3 H 2e- ---gt PbSO4 2
  H2O

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Ni-Cad Battery

• Anode (-)
• Cd 2 OH- ---gt Cd(OH)2 2e-
• Cathode ()
• NiO(OH) H2O e- ---gt Ni(OH)2 OH-

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Electrolysis

• Using electrical energy to produce chemical
  change.
• Sn2(aq) 2 Cl-(aq) ---gt Sn(s) Cl2(g)

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Electrolysis of Aqueous NaOH
Electric Energy ----gt Chemical Change

• Anode ()
• 4 OH- ---gt O2(g) 2 H2O 4e-
• Cathode (-)
• 4 H2O 4e- ---gt 2 H2 4 OH-
• Eo for cell -1.23 V

Anode
Cathode
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Electrolysis Electric Energy ---gt Chemical
Change
  Electrolysis of molten NaCl.   Here a battery
pumps electrons from Cl- to Na.   NOTE
Polarity of electrodes is reversed from batteries.
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Electrolysis of Molten NaCl
Figure 20.18
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Electrolysis of Molten NaCl

• Anode ()
• 2 Cl- ---gt Cl2(g) 2e-
• Cathode (-)
• Na e- ---gt Na

Eo for cell (in water) Ec - Ea - 2.71 V
(1.36 V) - 4.07 V (in water) External
energy needed because Eo is (-).
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Electrolysis of Aqueous NaCl

• Anode ()
• 2 Cl- ---gt
• Cl2(g) 2e-
• Cathode (-)
• 2 H2O 2e- ---gt
• H2 2 OH-
• Eo for cell -2.19 V
• Note that H2O is more easily reduced than
  Na.

Also, Cl- is oxidized in preference to H2O
because of kinetics.
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Electrolysis of Aqueous NaCl

• Cells like these are the source of NaOH and Cl2.
• In 1995 25.1 x 109 lb Cl2 and 26.1 x 109 lb NaOH

Also the source of NaOCl for use in bleach.
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Electrolysis of Aqueous NaI

• Anode () 2 I- ---gt I2(g) 2e-
• Cathode (-) 2 H2O 2e- ---gt H2 2 OH-
• Eo for cell -1.36 V

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Electrolysis of Aqueous CuCl2

• Anode ()
• 2 Cl- ---gt Cl2(g) 2e-
• Cathode (-)
• Cu2 2e- ---gt Cu
• Eo for cell -1.02 V
• Note that Cu is more easily reduced than either
  H2O or Na.

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Electrolytic Refining of Copper
Figure 22.11
Impure copper is oxidized to Cu2 at the anode.
The aqueous Cu2 ions are reduced to Cu metal at
the cathode.
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Producing Aluminum

• 2 Al2O3 3 C ---gt 4 Al 3 CO2

Charles Hall (1863-1914) developed electrolysis
process. Founded Alcoa.
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Michael Faraday1791-1867

• Originated the terms anode, cathode, anion,
  cation, electrode.
• Discoverer of
• electrolysis
• magnetic props. of matter
• electromagnetic induction
• benzene and other organic chemicals
• Was a popular lecturer.

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Eo and Thermodynamics

• Eo is related to ?Go, the free energy change for
  the reaction.
• ?G proportional to nE
• ?Go -nFEo
• where F Faraday constant 9.6485 x
  104 J/Vmol of e-
• (or 9.6485 x 104 coulombs/mol)
• and n is the number of moles of electrons
  transferred

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Eo and ?Go

• ?Go - n F Eo
• For a product-favored reaction
• Reactants ----gt Products
• ?Go lt 0 and so Eo gt 0
• Eo is positive
• For a reactant-favored reaction
• Reactants lt---- Products
• ?Go gt 0 and so Eo lt 0
• Eo is negative

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Quantitative Aspects of Electrochemistry

• Consider electrolysis of aqueous silver ion.
• Ag (aq) e- ---gt Ag(s)
• 1 mol e- ---gt 1 mol Ag
• If we could measure the moles of e-, we could
  know the quantity of Ag formed.
• But how to measure moles of e-?

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Quantitative Aspects of Electrochemistry

• But how is charge related to moles of electrons?

96,500 C/mol e- 1 Faraday
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Quantitative Aspects of Electrochemistry

• 1.50 amps flow thru a Ag(aq) solution for 15.0
  min. What mass of Ag metal is deposited?
• Solution
• (a) Calc. charge
• Charge (C) current (A) x time (t)
• (1.5 amps)(15.0 min)(60 s/min) 1350 C

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Quantitative Aspects of Electrochemistry
1.50 amps flow thru a Ag(aq) solution for 15.0
min. What mass of Ag metal is deposited?

• Solution
• (a) Charge 1350 C
• (b) Calculate moles of e- used

(c) Calc. quantity of Ag
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Quantitative Aspects of Electrochemistry

• The anode reaction in a lead storage battery is
• Pb(s) HSO4-(aq) ---gt PbSO4(s) H(aq) 2e-
• If a battery delivers 1.50 amp, and you have 454
  g of Pb, how long will the battery last?
• Solution
• a) 454 g Pb 2.19 mol Pb
• b) Calculate moles of e-

c) Calculate charge 4.38 mol e- 96,500 C/mol
e- 423,000 C
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Quantitative Aspects of Electrochemistry

• The anode reaction in a lead storage battery is
• Pb(s) HSO4-(aq) ---gt PbSO4(s) H(aq) 2e-
• If a battery delivers 1.50 amp, and you have 454
  g of Pb, how long will the battery last?
• Solution
• a) 454 g Pb 2.19 mol Pb
• b) Mol of e- 4.38 mol
• c) Charge 423,000 C

d) Calculate time
About 78 hours