Compact Fluorescent Lamp

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Batteries

• Katy Swancutt
• ENGR 302I
• December 2007

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What is a battery?

• It is something that converts chemical energy
  into electrical energy.
• They produce current via redox reactions
• Redreduction (gaining electrons)
• Oxoxidation (losing electrons)
• Batteries are essentially Voltaic Cells connected
  in series.

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What is a voltaic cell?

• Major components
• Metals

ZINC
COPPER
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What is a voltaic cell?

• Major components
• Metals
• Electrolytes

ZINC
ZnSO4(aq)
CuSO4(aq)
COPPER
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What is a voltaic cell?

• Major components
• Metals
• Electrolytes
• Salt Bridge
• Wire

ZINC
ZnSO4(aq 1.0 Molar
AGAR
Battery lifetime depends on the mass of metal in
the electrodes.
WIRE
CuSO4(aq) 1.0 Molar
COPPER
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What is a voltaic cell?
ZINC
ZnSO4(aq)
AGAR
WIRE
CuSO4(aq)
COPPER
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How does it make energy?

• The solid zinc anode oxidizes and becomes Zn2
• Electrons travel through the wire toward the
  cathode
• The aqueous Cu2 is reduced and adds to the solid
  copper cathode

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How much energy can it make?

• You can predict the voltage (direct current)
  between any two materials based on reduction
  potentials.
• A reduction potential, Eocell, is the difference
  between the standard reduction potential of the
  cathode (Eored(cathode)) and the anode
  (Eored(anode)).
• Eocell Eored(cathode)-Eored(anode)

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How much energy can it make?

• Step 1 Write the reaction. Zn(s)Cu2(aq)?Zn
  2(aq)Cu(s)
• Step 2 Look up values.
• Eored(cathode) 0.337V
• Eored(anode) -0.763V
• Eocell 0.337V-(-0.763V)
• Eocell 1.10V
• Actual voltage1.044V

1.044 Volts
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How can you get more energy?

• Connect several cells in series
  (1.044V1.044V1.044V)
• Work outside of standard conditions
  (concentration, temp, etc.)
• Use different compounds for the electrodes.
• The greatest voltages are from a combination of
  the compound with the most negative potential
  (anode) and the most positive (cathode). These
  happen to be Li and F, respectively.

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Electrode Combinations
Below Magnesium anode and Zinc cathode Expected
Vocell1.607V Observed Vocell0.63V
Above Zinc anode and IronIII cathode Expected
Vocell1.534V Observed Vocell0.70V
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Electrode Combinations
Below Magnesium anode and Copper
cathode Expected Vocell2.707V Observed
Vocell1.923V
Above IronIII anode and Copper cathode Expected
Vocell0.434V Observed Vocell0.432V
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Electrode Combinations
Above Magnesium anode and IronIII
cathode Expected Vocell3.141V Observed
Vocell1.373V
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Environmental Impacts

• Some electrodes are made of hazardous materials
• Cadmium in Ni-Cd batteries
• Lead in lead-acid batteries (like a car battery)
• Mercury-electrode batteries (banned in 1996)
• Arsenic and Antimony in lead-acid
  batteries

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Environmental Impacts

• When batteries are not recycled, they ultimately
  end up contaminating soil, air, water, and
  finally end up in the food chain.
• Using secondary (rechargeable) batteries helps to
  prevent pollution.

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THANK YOU!