1. From Chemistry to Electricity
Galvanic Cells
From Chemistry to Electricity

2. From Chemistry to Electricity . . . And back again!
Electrolytic Cells
From Chemistry to Electricity And back again!

3. Recall: the Galvanic Cell
Zn2+
Cu2+
Cu(s)
Zn(s)
Zn2+
Zn2+
Cu2+
Cu2+

4. Recall: the Galvanic Cell
Load
Current →
Conductor
Salt Bridge
Zn2+
Cu2+
Cu(s)
Zn(s)
Electrolyte
Anode
Cathode
Zn2+
Cu(s)
Zn2+
Cu2+
Oxidation happens here
Reduction happens here

5. Questions: Which way did the electrons go? Why?
What happens when we use a different pair of metals?

6. 
Voltage
Voltage is also known as electromotive force and potential difference
It is a measure of how much energy electrons have to get them moving
It is related to the distance between two metals are on the activity series

7. Analogy Potential Difference e- e- Lithium Potassium Barium Calcium
Sodium
Magnesium
Aluminium
Zinc
Iron
Nickel
Lead
(Hydrogen)
Copper
Silver
Gold
Analogy e- e-
Potential Difference

8. Question:
Can we push the electrons back up again?

9.  The Electrolytic Cell + - External Voltage Na+ Anode Cl- Cathode
Electrolyte: eg. NaCl

10.  The Electrolytic Cell + - External Voltage Cl2(g) Na(s) Anode
Cathode
Electrolyte: eg. NaCl

11. Similarities and Differences
Similarities and Differences
Galvanic Cells
Oxidation occurs at the anode
Reduction occurs at the cathode
Anode is negative
Cathode is positive
Does not require external voltage source
Changes chemical reactions into electrical energy
Electrolytic Cells
Oxidation occurs at the anode
Reduction occurs at the cathode
Anode is positive
Cathode is negative
Requires external voltage source
Changes electrical energy into chemical reactions

12. Etymology
Electrolysis comes from two Greek words: electron and lysis (meaning to break.) Therefore, the word means “breaking apart using electrons

13. Water Reaction 2 H2O(l) → O2(g) + 4 H+(aq) + 4 e-
2 H2O(l) + 2 e- → H2(g) + 2 OH-(aq)

14. Water Reaction 2 H2O(l) → O2(g) + 4 H+(aq) + 4 e-
4 H2O(l) + 4 e- → 2 H2(g) + 4 OH-(aq)
6 H2O(l) → 2 H2(g) + O2(g) + 4 H+ + 4 OH-(aq)

15. The Electrolytic Cell + - O2(g) H2(g) External Voltage Anode Cathode
Electrolyte

16. Practice Where would the hydrolysis reaction be useful?
Draw an electrolytic cell for AgBr(l).
Draw a galvanic cell for the reaction
Au+3 (aq) + Ag(s)  Ag+1 (aq) + Au (s)