1. Electrochemistry

2. Electrochemical Cells/ Chemical Cells
Also called voltaic or galvanic cells
A redox reaction produces electricity
Occurs spontaneously

3. Electrochemical Cell

4. Half Cells Each ½ of the redox reaction occurs in a separate container
One for oxidation and one for reduction
They are connected by a salt bridge
Salt Bridge: allows ions to flow between the two cells

5. Electrodes
Metals which provide a surface for oxidation or reduction to occur
Solids
Oxidation Number = 0
Anode
Cathode

6. Reduction at the Cathode
ANODE
Oxidation occurs at the anode
Negative electrode
CATHODE
Reduction occurs at the cathode
Positive electrode
Red Cat – An Ox
Reduction at the Cathode
Oxidation at the Anode

7. Flow of Electrons The electrodes are connected by a wire
Electrons flow from the anode to the cathode through the wire

8. Why does the cell produce electricity?
There is a difference of electric potential between the two electrodes
Electrons will flow between the two electrodes until equilibrium is reached
At equilibrium the cell’s voltage would be zero

9. - + Zn + CuSO4 Cu + ZnSO4 Zn Zn2+ + 2e- Cu2+ + 2e - Cu0 e- e- e- e- e-
Red Cat -reduction takes place…electrons are gained.
An Ox -oxidation takes place…electrons are lost.
Zn Zn2+ + 2e-
Cu2+ + 2e Cu0 e- e- e- e- e- - e- + e- e-
Electrons needed here for reduction
Electrons released here by oxidation e- e- e-

10. Batteries
Use a redox reaction which produces electricity spontaneously
Batteries are recharged by reversing the reaction
Dry Cell (Acid or Alkaline), Lead Storage (Car), Rechargeable (Ni/Cd)

11. Corrosion Oxidation of a metal
Metal combines with element (usually oxygen)
Example: 4Fe + O Fe2O3 (rust)

12. Prevention of Rust
Cover the metal – paint, oil, another (more reactive) metal
Cathodic Prevention
metal is placed in contact with a more reactive metal
That metal will be oxidized (acts as the anode), the original metal acts as the cathode
Alloys – mixture of metals
Brass, stainless steel (Fe + Cr), cast iron (C + Si)

13. Electrolytic Cells Also called electrolysis
An electric current is used to produce a chemical reaction
An electric current is used to force a non-spontaneous reaction to occur

14. Oxidation occurs at the anode Reduction occurs at the cathode
Electrons flow from anode to cathode
The cathode is the negative electrode
The anode is the positive electrode
This is opposite of the chemical cell because the external current causes the polarities to switch

16. Electroplating Object to be plated is the CATHODE, negative
Metal to be plated onto the object is the ANODE, positive
Solution must contain ions of the metal to be plated

17. Silver Plating Cathode = Anode = Solution =
What happens to the mass of each electrode during the reaction?

18. Electrolysis of Water 2 H2O  2 H2 + O2
The H+ is reduced at the (-) cathode, producing H2 (g), which is trapped in the tube
The O2 is oxidized at the (+) anode, yielding O2 (g), which is trapped in the tube

19. Hydrogen Fuel Cells
Uses hydrogen gas as the fuel
2 H2 + O2  2 H2O