1. Electrochemical Cells (Batteries)
Chemical reaction produces electricity.
Called “voltaic cells”
Happens SPONTANEOUSLY.

2. Moving Electrons = Electricity
Electrons from oxidized substance
travel towards substance reduced.
Traveling electrons move
through “external circuit”
where they do work.

3. Parts of a Simple Battery (Voltaic Cell)
Made of Two “Half Cells” containing:
2 Metal Electrodes
2 Solutions of Ions
External Wire
Salt Bridge
Zinc Copper Galvanic Cell: 2:30

4. “Charge” (as either electrons or ions)
flows in a “circuit” that is connected in a
continuous loop.
External Wire:
allows ELECTRONS
to flow between
metal electrodes
Salt Bridge:
Allows IONS to flow
between salt solutions

5. What is Ox/Red? Start with Table J Electrons travel from more
“Active” metal toward less
active metal.
Metal above = oxidized
Ion on Metal below = reduced
Ex:
Ox: Zn
Red: Cu+2

6. flow in the external wire?
Which way do electrons
flow in the external wire?
Electrons flow
“Down Table J”
From oxidized metal
above to positive ion of
metal below
from Zn to Cu+2 e-

7. Which electrode is negative or positive? e-
Electrons flow from negative to
positive electrode.
Negative electrode: Zn
Positive electrode: Cu e-

8. Which electrode is the anode or cathode? Anode: metal electrode
where oxidation occurs
Ex: Zn
Cathode: metal electrode
where reduction occurs
Ex: Cu
Note: Electrodes are always pieces
of pure metal (not ions)

9. Remember AN OX RED CAT Anode is where oxidation happens
Cathode is where reduction happens

10. What are the Half Reactions?
Ox:
Zn0 Zn+2 + 2e-
Red:
Cu+2 + 2e- Cu0
What is the Net Equation?
Net: (add ½ reactions)
Zn0 + Cu+2 Zn+2 + Cu0
Make sure final net equation is
balanced for electrons and atoms!
Galvanic Cell Animation 2:00 e-

11. Which electrode gains/loses weight?
Look at half reactions!!
Which forms solid metal?
Which forms dissolved ions?
Ox:
Zn0 Zn+2 + 2e-
Red:
Cu+2 + 2e- Cu0
Dissolved ion
Solid metal

12. “The negative ions complete the circuit”
Which way do the ions in the salt
bridge “migrate” or move?
Remember:
“The negative ions complete the circuit”
(The ions actually end up moving towards
the solution of opposite charge that forms.)
1:30

13. Draw and label Battery Mg/Mg+2//Al+3/Al
What is oxidized ________reduced_______
Neg. electrode_____ Positive electrode____
What is the anode _______cathode_______
Which way do e- flow in wire? To the ________
+ ions flow _____ - ions flow _____in salt bridge?
Table J Mg Al

14. Mg/Mg+2//Al+3/Al Battery
Ox. Half Reaction: Red. Half Reaction: Net Equation: Which electrode gains mass ____ Which electrode loses mass ____

15. Means the reaction in the battery has
Dead Battery
Voltage = 0
Means the reaction in the battery has
reached EQUILIBRIUM.

16. Practice
 Given the balanced ionic equation representing the reaction in an operating voltaic cell: Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)
The flow of electrons through the external circuit in this cell is from the
(1) Cu anode to the Zn cathode
(2) Cu cathode to the Zn anode
(3) Zn anode to the Cu cathode
(4) Zn cathode to the Cu anode

17. In the completed external circuit, the electrons flow from
Given the balanced equation representing the reaction occurring in a voltaic cell: Zn(s) + Pb2+(aq) Zn2+(aq) + Pb(s)
In the completed external circuit, the electrons flow from
(1) Pb(s) to Zn(s)
(2) Pb2+(aq) to Zn2+(aq)
(3) Zn(s) to Pb(s)
(4) Zn2+(aq) to Pb2+(aq)

18. Which statement is true for any electrochemical cell?
(1) Oxidation occurs at the anode, only.
(2) Reduction occurs at the anode, only.
(3) Oxidation occurs at both the anode and cathode.
(4) Reduction occurs at both the anode and cathode

19. Finding Voltage of a Battery (Honors)
Use Voltage Table
Find your half reactions and record voltage
Note:
All ½ reactions shown are reductions.
For oxidation, reverse the sign of the voltage
DO NOT multiply voltage by coefficients in balanced eq.

20. Nerntz Equation (Honors)