1. Section 10.3—Batteries & Redox Reactions
How do we harness the electricity to form a battery?

2. 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.

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

4. What Makes up a Voltaic Cell?
If the 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

5. 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.

6. What Makes up a Voltaic Cell?
Voltaic cells are made of several components.
Salt Bridge
Anode Oxidation occurs - + - + - + +
Cathode
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.

7. Line Notation
Line Notation – A short-hand method of describing the components of a voltaic cell

8. 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)

9. 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)

10. How is Electricity Measured?
As electrons change places in a redox reaction, they have a different potential energy
The difference in potential energy as the electron moves is how electricity is measured.
Electrons have potential energy based on their position
The potential difference (or Electromotive Force, EMF or E) is measured in Volts (V)

11. 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!

12. Calculating Cell Potential
An oxidation reaction is the opposite process from reduction
Therefore the oxidation potential is “- reduction potential”
The table lists standard reduction potential
Remember—the number of atoms or moles doesn’t matter…don’t multiple reduction potentials by balanced equation coefficients!

13. Cell Potential & Spontaneity
A spontaneous reaction is one that occurs on its own
A voltaic cell will operate spontaneously if the EMF is positive

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

15. Determine if a cell will react as written spontaneously:
Example #2
Example
Determine if a cell will react as written spontaneously:
Fe+3 + Cu  Cu+2 + Fe+2
Fe+3  Fe reduction (cathode)
Cu  Cu oxidation (anode)
Look up standard reduction potentials:
Fe+3 + e-1  Fe V
Cu e-1  Cu V
EMF = 0.40 V
It will proceed spontaneously

16. 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.

17. 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

18. Batteries as Electrolytic Cells
When a battery is being re-charged, it’s acting as an electrolytic cell!

19. What did you learn about batteries?

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