# Lesson 12: potential difference ```Cell Potential
Objective
lesson 3
chapter 13
You will be able to calculate the potential
difference of a voltaic cell
Standard Cell
Definition
A voltaic cell in which all of the electrolytic solutions are at
1.0 mol/L and they are at SATP.
Recall SATP is 25˚C and 101.325 kPa.
Symbol is E˚
It is a measure of the potential energy (voltage) of the
electrons in the cell.
It depends upon the
&middot; Make up of the half cells
&middot; Concentration of the electrolytes
&middot; temperature
Reduction Half Potential
Each half reaction in the data book has a standard
reduction potential associated with it. (E˚R)
This is a measure of the attraction for electrons.
The stronger the OA, the higher the reduction potential.
Cell Potential
Cathode
Positive electrode
The half cell with the greater reduction potential.
Anode
Negative electrode
Has lower reduction potential
E˚cell = E˚cathode – E˚anode
Example 1
What is the cell potential of a voltaic cell that is
composed of a copper half cell and a silver half cell?
Note
A positive number indicates a spontaneous reaction.
Example 2
What is the standard cell potential of a voltaic cell
composed of cadmium and zinc half cells.
Measuring Cell Potential Difference
Potential differences are measured with a voltmeter.
A voltmeter measures the difference in potential
between two areas. This means that it must be
measured across both half cells.
Since a half cell cannot have a potential difference, it
must be compared to a reference cell.
Reference Half Cell
Hydrogen was arbitrarily chosen as the reference point.
You will notice from the listing of E˚ that the reaction that
has a potential of zero is
+
2H (aq) + 2e H2(g)
Example 3
A hydrogen half cell is connected to an I2 | I-(iodine |
iodide) half cell.
Label the cathode, anode and write the half reactions.
Example 4
Label the electrodes, write the half reactions, and
calculate the cell potential for an aluminum and
hydrogen cell.
If another element had been chosen as the reference
cell, how would that affect the half cell potentials?
How would it affect cell potentials?
Example 5
Determine a revised set of cell potentials for copper,
zinc, and hydrogen if copper is assigned a potential of
zero.
Cu2+ + 2e-➔Cu +0.34 V 0.00 V
2H+ + 2e- ➔  H 0.00 V
2
Zn2+ + 2e- ➔  Zn-0.76 V
Assignment
Do the worksheet.
0.00 V
```