ElectrochemistryOxidation-Reduction
Dr. Ron RusaySpring 2004
© Copyright 2004 R.J. Rusay© Copyright 2004 R.J. Rusay
Oxidation-Reduction
• Oxidation is the loss of electrons.• Reduction is the gain of electrons.• The reactions occur together. One does not
occur without the other.• The terms are used relative to the change in
the oxidation state of the reactant(s).
Oxidation State(Oxidation Number)
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Cu 2+ Cu (s)
H2 (g) 2 H +
0
0
+2 e-
- 2 e-
Use oxidation numbers to determine what is oxidized and what is reduced.
Number of electrons gained must equal the number of electrons lost.
- 2 e-
+2 e-
Voltaic CellsVoltaic Cells
Voltages of Some Common Voltaic Cells
Voltaic Cell Voltage (V)
Common alkaline battery 1.5
Lead-acid car battery (6 cells = 12 V) 2.0
Calculator battery (mercury) 1.3
Electric eel (~ 5000 cells in 6-ft eel = 750 V) 0.15
Nerve of giant squid (across cell membrane) 0.070
Automotive Application: the Discharge and Recharging of a Lead-Acid Battery
Lithium Solid-State Battery
Nickel-Cadmium(Nicad) Battery
Flow Batteries (Fuel Cells)
The Hydrogen Oxygen Fuel Cell
Anode (oxidation):H2 (g) + CO3
2-(l) H2O(g) + CO2 (g) + 2 e-
Cathode (reduction): 1/2 O2 (g) + CO2 (g) + 2 e- CO3
2-(l)
Overall (cell) reaction:H2 (g) + 1/2 O2 (g) H2O(g) Ecell = 1.2 V
Other Fuel Cells:2 NH3 (g) + 3/2 O2 (g) N2 (g) + 3 H2O(l)
N2H4 (g) + O2 (g) N2 (g) + 2 H2O (l)
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O(l)
Chemistry of Batteries
Comparison of Voltaic and Electrolytic Cells
Electrode
Cell Type G Ecell Name Process Sign
Voltaic < 0 > 0 Anode Oxidation -
Voltaic < 0 > 0 Cathode Reduction +
Electrolytic > 0 < 0 Anode Oxidation +
Electrolytic > 0 < 0 Cathode Reduction -
Electrochemical Reactions
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Electrolysis: Chrome Plating
Aluminum ProductionUsing an Electrolytic Cell
Do you recycle? It takes only 5% of the energy to produce a can from recycled aluminum vs. aluminum ore.