1. Cell Potential and the Nernst Equation
Electrochemistry
Cell Potential and the Nernst Equation

2. The Electrochemical Cell Lead-Acid (car) Battery
Producing Copper Lab
Source:
Source:
Alkaline Battery
Lead-Acid (car) Battery

3. The Electrochemical Cell
The species being oxidized LOSES electrons
Occurs at the anode (both start with vowels!)
is the reducing agent
is the more active metal
Will go from metal to ion, thus putting out electrons
From the producing copper lab…
2Cl- (aq) → Cl2 (g) + 2e-

4. The Electrochemical Cell
The species being reduced GAINS electrons
Occurs at the cathode (both start with consonants!)
is the oxidizing agent
is the less active metal
Will go from ion to metal, thus taking in electrons
From the producing copper lab…
Cu+2 (aq) + 2e- → Cu (s)

5. The Electrochemical Cell Cu2+ (aq) + Zn (s) → Zn2+ (aq) + Cu (s)
Copper
Zinc
CuSO4
ZnSO4
Write the oxidation half-reaction
Write the reduction half-reaction
What is the oxidizing agent?
What is the reducing agent?
Where is the cathode?
Where is the anode?
Image:

6. The Electrochemical Cell Cu2+ (aq) + Zn (s) → Zn2+ (aq) + Cu (s)
Copper
Zinc
CuSO4
ZnSO4
How can we determine the voltage (the cell potential) created by an electrochemical cell?
Electrons flow from anode to cathode. We can measure this.
Image:

7. The Electrochemical Cell Cu2+ (aq) + Zn (s) → Zn2+ (aq) + Cu (s)

8. Determining Cell Potentials Ecell = Eoreduction + Eooxidation
Write the oxidation and reduction half-reactions
Use the standard reduction table to determine:
Ecell = Eoreduction + Eooxidation
*Remember to flip the sign if you flip the half-reaction!
Determine if spontaneous or not:
+ Ecell = spontaneous
- Ecell = not spontaneous

9. Cell Potential Example
Determine the cell potential and say if the reaction is spontaneous as written:
Mn2+(aq) + 4H2O(l) + Sn2+(aq) → MnO4-(aq) + 8H+(aq) + Sn(s)

10. The Nernst Equation
Until now, we have been calculating cell potentials at standard conditions (1 M, 25oC, and 1 atm).
How do we calculate cell potentials under NON standard conditions?
At standard temp, this simplifies to:

11. Nernst Equation Example
Find the cell potential for the following reaction at 25°C if [Cd2+] = M and [Pb2+] = M.
Cd2+ (aq) + Pb (s) → Pb2+ (aq) + Cd (s)