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							              Section 10.3—Batteries &
                      Redox Reactions



How do we harness the electricity to form a battery?
Voltaic Cells & Electricity

   Voltaic Cell (also called Galvanic
   Cell) – Turns chemical energy into
   electrical energy.
    They separate the reduction reaction from the oxidation
    reaction and harness the electricity as electrons flow from one
    side to the other



   Electricity – Flow of electrons over a
   wire.
What Makes up a Voltaic Cell?




  If both the reduction and oxidation reaction happened in one
  container together, there would be no way to harness the
  electricity
What Makes up a Voltaic Cell?




  If both the reduction and oxidation reaction happened in one
  container together, there would be no way to harness the
  electricity
  Electrons flow from the oxidation compartment to the reduction
  compartment
What Makes up a Voltaic Cell?

  Anode
Oxidation
  occurs                                                         Cathode
                                                                 Reduction
                                                                 occurs




   Metal and a wire are needed for the electrons to flow from
   one compartment to another.

   If the redox reactions include solid metals, then those are
   used to conduct the electrons
   If not, a non-reactive metal (such as platinum) is used.
What Makes up a Voltaic Cell?
   Voltaic cells are made of several components.
                                                Salt Bridge
  Anode
Oxidation                     -+- + -
                                        +                     Cathode
  occurs                 -+                 +
                                                -             Reduction
                     +                              +         occurs
            -        -                              -
                    -
             -


   Over time, there will be a build up of negative charge in the
   reduction compartment.
   This would cause the cell to stop when enough charge builds up.
   A salt bridge is added. As negative electrons flow to the
   reduction compartment, ions in the salt bridge flow to balance
   the charge.
Line Notation



  Line Notation – A short-hand method
  of describing the components of a
  voltaic cell
Line Notation
   The oxidation reaction (anode) is always written first.
   The reactant is written first for each half-reaction.
   The anode and cathode are separated by a “║”
   Different states of matter are separated by a “│”
   Species of the same state of matter are separated by a “,”

                     Example
            Write the line notation for:
      Mg (s) + Al+3 (aq)  Mg+2 (aq) + Al (s)
Line Notation
   The oxidation reaction (anode) is always written first.
   The reactant is written first for each half-reaction.
   The anode and cathode are separated by a “║”
   Different states of matter are separated by a “│”
   Species of the same state of matter are separated by a “,”

                     Example
            Write the line notation for:
      Mg (s) + Al+3 (aq)  Mg+2 (aq) + Al (s)

        Mg0  Mg+2 is oxidation reaction (anode)
        Al+3  Al0 is the reduction reaction (cathode)

                   Mg (s)│Mg+2 (aq) ║ Al+3 (aq) │Al (s)
How is Electricity Measured?

                         As electrons
                           change places          The difference in
 Electrons have            in a redox               potential energy
    potential              reaction, they           as the electron
    energy based           have a                   moves is how
    on their               different                electricity is
    position               potential                measured.
                           energy




The potential difference (or Electromotive Force, EMF or E) is
measured in Volts (V)
Standard Reduction Potential

  Standard Reduction Potential –
  Electromotive Force (EMF) produced
  when a reduction reaction occurs with
  hydrogen as the reference.

   The hydrogen reaction has been defined as “0” and all others
   are compared to it.

   Standard Reduction Potential is an intensive property…it doesn’t
   matter how many atoms undergo the change, the Standard
   Reduction Potential is the same!
Calculating Cell Potential

  The table lists          An oxidation              Therefore the
    standard                 reaction is the           oxidation
    reduction                opposite                  potential is
    potential                process from              “- reduction
                             reduction                 potential”




         EMF  reduction potential reduction reaction
            cell

                       reduction potential oxidation reaction

                      EMF  cathode anode

Remember—the number of atoms or moles doesn’t matter…don’t
multiple reduction potentials by balanced equation coefficients!
Cell Potential & Spontaneity

A spontaneous reaction is one that occurs
 on its own
A voltaic cell will operate spontaneously if
 the EMF is positive
Example #2

                 Example
   Determine if a cell will react as written
              spontaneously:
         Fe+3 + Cu  Cu+2 + Fe+2
Example #2

                  Example
    Determine if a cell will react as written
               spontaneously:
          Fe+3 + Cu  Cu+2 + Fe+2


  Fe+3  Fe+2       reduction (cathode)
  Cu  Cu+2         oxidation (anode)

  Look up standard reduction potentials:        EMF  cathode anode
  Fe+3 + e-1  Fe+2    0.77V
  Cu+2 + 2 e-1  Cu      0.34 V                  EMF  0.77V  0.34V


                         EMF = 0.40 V
                         It will proceed spontaneously
Electrolysis & Electrolytic Cell


   Electrolysis – Putting in electrical
   energy to force a redox reaction in the
   non-spontaneous direction.


   Electrolytic Cell – Cell that converts
   electricity to chemical energy.
Electrolytic Cell Example
  To force a cell in the non-spontaneous direction,
  you must put in at least the voltage that is
  produced from the spontaneous process.

             Produces 0.44 V Spontaneously




        Fe+3 + Cu  Cu+2 + Fe+2


           Requires at least 0.44 V to push in
              non-spontaneous direction
Batteries as Electrolytic Cells

When a battery is being re-charged, it’s
 acting as an electrolytic cell!
What did you learn about
               batteries?
  Batteries
                                     When being
                   are               recharged are


           Voltaic                           Electrolytic
            Cells                               cells
                              Force a non-
Which produce                 spontaneous
     electricity                                                      Oxidation
       through
                                                          When lost
          Oxidation-             Is
          Reduction              transfer        Electrons
                                 of
          Reaction
                                                             When gained
                   One type
                                                                      Reduction
              Single               Possibility
                                  determined         Activity
          replacement
                                      by             Series
            reactions