1. Electrochemistry - Section 1 Voltaic Cells
Chemistry - Chapter 21
Electrochemistry - Section 1
Voltaic Cells

2. Half-Reactions
Two terms that you must know:
Oxidation
Reduction

3. Half-Reactions Two terms that you must know: Oxidation
The process of loosing electrons
Example: Zn  Zn e-

4. Half-Reactions Two terms that you must know: Reduction
The process of gaining electrons
Example: Cu e-  Cu

5. Half-Reactions Two terms that you must know:
Oxidation and reduction occur in pairs in all chemical reactions
Remember this: OIL RIG
(Oxidation Is Loosing, Reduction Is Gaining)

6. Setting up the Redox Reaction
Keeping the Half-Reactions separate is important.
Creating a path for the flow of electrons is a must! (done with a wire and salt bridge)

7. Electrochemical Cells
The Salt Bridge
allows the
charge to
balance.

8. Electrochemical Cells
Note that the metal
strip is in contact
with a solution that
is similar.
i.e. Zinc in a solution
of zinc nitrate and
copper in solution
of copper II nitrate.

9. Half-Reactions and Cells
Each cell has a half-reaction taking place within.
The oxidation takes place at the anode
The reduction takes place at the cathode
The reaction proceeds in such a way as to end with a more stable system: the electrical potential of the cell

10. Calculating Cell Potential
Reduction potential is the tendency of a substance to gain electrons.
Measured in volts
Must be determined in connection with another substance
Determine the difference in potential of the two cells
Standard Hydrogen electrode is used to compare all cells
This cell is defined as having a potential of 0.0 V

12. Calculating Cell Potential
One like this
is found on
page 667 in
your text

13. Calculating Cell Potential
The value of the cell potential is calculated by subtraction of the standard reduction potential of the oxidation half-reaction from the standard reduction potential of the reduction half reaction.
Eocell
Eoreduction
Eooxidation = -

14. Calculating Cell Potential
Using cell notation we see this:
Cu(s)ᅵCu2+(aq)║Zn2+(aq)ᅵZn(s)
Cathode half-cell
Anode half-cell
Salt Bridge

15. Calculating Cell Potential
Eocell = EoCu2+ǀCu - EoZnǀZn2+
For this reaction, then, we have the
following:
Eocell = V - ( V)
= V