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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!
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

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