Electrochemistry

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Electrochemistry
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• Terms used with electricity
• Galvanometer - an instrument for detecting
  electric current.
• Voltmeter - an instrument to measure the
  potential difference between two half-cells in a
  voltaic cell.
• Amperes - the SI units for current flow   e-
  / s
• Volts - a measurement of electric potential
  difference between two electrodes.
• Electromotive force, emf - another term for
  volts.
• Cations - positive ions attracted to the cathode.
  
• Anions - negative ions attracted to the anode.
• Electrolysis - the process by which an electric
  current produces a chemical change.
• Voltaic cell - a device used to produce electric
  energy from an oxidation-reduction reaction.
• Battery - two or more electrochemical cells
  operating as a unit.
• External circuit - a "wires" connected to a
  battery providing a path for electricity to flow.
  
• Internal circuit - the electrolyte inside a
  battery through which ions can move.

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The cell works because the valence electrons of
zinc have a higher energy than the valence
electrons of copper. This gives zinc a greater
tendency to give up electrons than copper. In the
external circuit, electrons will always move from
the positive anode to the negative cathode.

• Zinc is the anode
• A piece of Zn metal is immersed in ZnSO4 (aq)
• Atoms of the zinc metal lose electrons and become
  zinc ions in solution.
• The half-reaction is represented by Zn    Zn2
  2e-

• A shorthand for representing the half-cell
  reaction is ZnZn2

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• Copper is the cathode
• A piece of Cu metal is immersed in CuSO4 (aq)
• Copper ions in solution gain electrons to add
  copper atoms to the copper metal.
• The half-reaction is represented by Cu2 2e-
     Cu

• A shorthand for representing the half-cell
  reaction is Cu2Cu
•   This cell operates because
• Copper metal takes electrons away from zinc
  metal.
• These electrons move from the anode to the
  cathode through the external circuit.
• The newly formed Zn2 go into solution.
• SO4-2 ions in solution move from the cathode to
  the anode through the salt bridge.
• The cell continues to operate as long as there is
  a potential energy difference between the
  half-cells.

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Redox Reaction Calculator    

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• 1.     Predict the direction chemical reactions
  will go.
• Will this reaction occur as written? Al3 (aq)
  Ni (cr)    Ni2 (aq) Al (cr)
• Total the voltage of the two half-reactions

• For a reaction to take place, there must
  be a positive voltage. This reaction will not
  spontaneously occur.
• 2.     Determine the maximum voltage produced
  by an electrochemical cell.
• What is the voltage of this cell?
  ZnZN2Fe2Fe
• Total the voltage of the two half-reactions

3.     Predict the products of electrolysis.
 
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Sample Problem Using the Reduction Table
Predict the products of the electrolysis of 1M
CuCl2 (aq)    The two possible reduction
reactions at the cathode are Cu2 2e-    Cu
. . . . 0.34V   2H2O 2e-    H2 2OH - . .
. . - 0.41V The least negative value requires
less energy, and will be the reaction to take
place. Cu (s) will be produced at the cathode.
   The two possible oxidation reactions at the
anode are 2Cl-    Cl2 2e- . . . . -1.362H2O
   O2 4H 4e- . . . . - 0.82    The
least negative, O2 (g) will be produced at the
anode.    Cu (s) and O2 (g) are produced by
electrolysis of 1M CuCl2 (aq)
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