1. Electrochemistry
Chapter 17

2. Electrochemistry is…
The study of the interchange of chemical and electrical energy.
Something we’ve already touched on. Remember:
Oxidation = loss of electrons, performed by reducing agent.
Reduction = gain of electrons, performed by oxidizing agent.
Balancing redox reactions via half-reactions.

3. Galvanic Cell
This is the device in which chemical energy is changed into electrical energy.
Parts:
Anode
Cathode
Salt Bridge

4. Cell Potential
The pull on electrons is the cell potential. This is sometimes called electrochemical force (emf)
The sum of the potential for each half reaction is equal to the cell potential of the reaction.
½ cell reduction potentials are based upon the assumption that the Hreaction is set to 0.

6. Calculating Cell Potential for a Reaction
The chart only gives reduction potentials.
One half will have to be reversed.
When a reaction is reversed, cell potential charge is reversed.
When a reaction is multiplied or divided by an integer, cell potential does NOT change.

7. Try Me
Write the balanced redox reaction and calculate the cell potential using this unbalanced equation:

8. Try Me Again
Find the cell potential and balanced equation for:

9. More Cell Potential Units are Volts (Joules/Coulomb)
Work flow out of the cell is negative. Thus, when the cell does work, cell potential is positive.
This value is a maximum amount…an ideal value

10. Line Notation for Cells
Anode, oxidation reaction on the LEFT
Cathode, reduction reaction on the RIGHT
Separated by 2 vertical lines (salt bridge).

11. How to Describe a Cell
Calculate the cell potential and write the balanced equation.
Discern the flow of electrons.
Pick out a substance for each electrode.
- If no conducting metal involved
in the rxn, use inert platinum
electrode.

12. Describe the Cell

13. Cell Potential and Gibbs
By a series of plugging in of equations, it can be determined that:
Positive Cell Potential = Negative Gibbs Energy
SPONTANEOUS!

14. Cell Potential and Concentration
All cell potentials are determined assuming solutions are 1M.
When concentration changes, LeChatelier rules apply.

15. Consider the Following:
[Al3+] = 2.0M, [Mn2+] = 1.0M
[Al3+] = 1.0M, [Mn2+] = 3.0M

16. A different Type of cell
Concentration Cell
Same contents on both sides of cell
Different concentrations
Electrons flow from low to high concentration.

17. The Nernst Equation!
Relates concentrations of the reaction to cell potential.
DG = DGo + RTln(Q)
–nFE = -nFEo + RTln(Q)
E = Eo + RTln(Q)
-nF
E = Eo – log (Q), at 25oC n
NERNST

18. Try Me! Calculate the cell potential when…
4H3BO3(aq) + 3O2(g)  4B(s) + 4O3(g) + 3H2O(l)
Eo = 1.48V [H3BO3]: 0.40M [O3]: 0.40M [O2]: 0.10M

19. Spontaneity of Cells
An electrochemical cell will discharge spontaneously until it reaches equilibrium.
At Equilibrium, Q = K and Eo = O, creating...
A DEAD BATTERY

20. Electrolysis
Forcing a current through a cell that causes the cell potential to be negative.
“undoing” the redox reaction

21. Stoichiometry of Electrolysis
An Ampere is a coulomb/second
If we know how long the reaction has gone on at a certain current, we know the charge.
1 mole of electrons has a charge of one Faraday, and 96,485 coulombs equal 1 Faraday (1 mole electrons / 96,485 Coulombs)

22. More Stoichiometry
Half reactions provide a mole ratio between electrons and reaction materials.

23. Try Me:
How long must a current of 5.00 A be applied to a solution of Ag+ to produce 10.5 g of silver metal?

24. Try Another:
What volumes of H2(g) and O2(g) at STP are produced from the electrolysis of water by a current of 2.50 A in 15.0 minutes?

25. Electrolysis Mixtures of Ions
Determine the order of reduction/oxidation processes done during electrolysis
Use standard reduction potentials.
More positive processes will occur first.
Water has an OVERVOLTAGE. This means it is a freak and actually requires more voltage than predicted.

26. Practice Problems: http://science.widener.edu/svb/tutorial/
Go to Chapter 20
Correctly complete 2 balancing redox reactions
Correctly complete 2 calculating Eo problems
Correctly complete 2 Faraday’s Laws problems
Correctly complete 2 Nernst Equation problems