Standard Reduction Potentials
So
how can we predict the voltage produced by two different reactions in
a galvanic cell (Eºcell)?
The answer is with “standard reduction potentials,” which you'll
find in a table in your textbook (or on Wikipedia).
This is best done with an example:
This is best done with an example:
|
Q: Find Eºcell for
|
 |
|
A: First, we need half-reactions. Note that we need 2 Cl- ions on the right side, since each Cl2 molecule has 2 chlorine atoms.
|
 |
Second,
we need to find the Eºcell
values for each of these reactions by looking them up in a table.
Third,
add these two reactions together to calculate Eºcell.
In reality, I would NOT write out the total reaction like I did here
... I'd just add together the Eº values to get the final answer.
But, it might help you to see what happened:
If
Eºcell
is positive, the reaction goes forward as written.
If Eºcell is negative, the reaction goes backwards from what is written.
If Eºcell is negative, the reaction goes backwards from what is written.
