1. from a battery or other external energy source
Electrolysis
Voltaic and galvanic cells use spontaneous redox reactions to generate electricity
Electrolysis is the opposite!
from a battery or other external energy source
Electrolysis uses electrical energy to FORCE a non-spontaneous redox reaction to occur.

2. Example: 2H2 + O2  2H2O -∆G Reduc: O2 + 4e-  2 O-2
Oxid: 2H2  4H e-

3. Example: 2H2 + O2  2H2O -∆G 2H2O  2H2 + O2 +∆G
e-’s flow spontaneously
Example:
Reduc: O e-  2 O-2
2H2 + O2  2H2O
-∆G
Oxid: 2H2  4H e-
Oxid: 2 O-2  O e-
2H2O  2H2 + O2
+∆G
Reduc: 4H e-  2H2
an external voltage must force the e-’s to flow

4. Doing Electrolysis Electrolysis takes place in an “electrolytic” cell
Oxid: 2 O-2  O e-
2H2O  2H2 + O2
+∆G
Reduc: 4H e-  2H2

5. Doing Electrolysis A power supply is needed, not a voltmeter
No need for two half cells
Electrodes are some other inert substance (C, Pt, Au)
Oxid: 2 O-2  O e-
2H2O  2H2 + O2
+∆G
Reduc: 4H e-  2H2

6. Doing Electrolysis A power supply is needed, not a voltmeter
No need for a salt bridge
The substance must be a liquid to allow particle flow
Oxid: 2 O-2  O e-
2H2O  2H2 + O2
+∆G
Reduc: 4H e-  2H2

7. Doing Electrolysis
RED CAT still applies, so e-’s still flow towards the cathode
Why bubbles???
Oxid: 2 O-2  O e-
2H2O  2H2 + O2
+∆G
Reduc: 4H e-  2H2

8. Other Electrolysis Examples:
Electrolysis of molten salts
Na(s) + Cl2(g)  NaCl -∆G
A voltage applied to molten NaCl will cause the reverse rxn to occur.
Answer the questions on the handout …

9. Other Electrolysis Examples:
Electrolysis of molten salts
a. What is the net reaction that occurs as a voltage is applied to molten sodium chloride?
NaCl(l)  Na(s) + Cl2(g)

10. Other Electrolysis Examples:
Electrolysis of molten salts
b. Write the two balanced half reactions that take place as the cell operates. Label which one takes place at the anode and which one takes place at the cathode.

11. Other Electrolysis Examples:
Electrolysis of molten salts
c. Bubbles will be observed at one of the inert electrodes being used in this cell. What half reaction is taking place there? Label it as the anode or cathode.

12. Other Electrolysis Examples:
Electrolysis of molten salts
d. The other electrode will increase it’s mass. What is being deposited on this electrode?

13. Other Electrolysis Examples:
Electrolysis of molten salts
e. What is the minimum voltage that must be applied to allow the cell to operate?

14. Other Electrolysis Examples:
2. Electrolysis of salt solutions
If electricity is applied to a salt solution, the oxidation / reduction could involve water OR could involve the ions

15. Other Electrolysis Examples:
Electrolysis of NaCl solution
Possible reductions:
2H2O + 2e-  H2 + 2OH-
Na+ + e-  Na(s)

16. Other Electrolysis Examples:
Electrolysis of NaCl solution
Possible oxidations:
2H2O  O H+ + 4e-
2Cl-  Cl2 + 2e-

17. Other Electrolysis Examples:
Electrolysis of NaCl solution
Answer the questions on the handout concerning the electrolytic cell shown.

18. Other Electrolysis Examples:
Electrolysis of NaCl solution
Answer the questions on the handout concerning the electrolytic cell shown.

19. Quantitative Stuff with Electrochemical Cells