Untitled - Kelly Walsh High School

Electrochemistry 271
We can use this table of standard reduction potentials to write the overall cell
reaction and to calculate the standard cell potential, the potential (voltage)
associated with the cell at standard conditions. There are a couple of things to
remember when using these standard reduction potentials to generate the cell
reaction and cell potential:
1. Since the standard cell potential is for a galvanic cell, it must be a positive
value, E > 0.
2. Since one half-reaction must involve oxidation, we must reverse one of the
half-reactions shown in the table of reduction potentials in order to indicate
the oxidation. If we reverse the half-reaction, we must also reverse the sign
of the standard reduction potential.
3. Since oxidation occurs at the anode and reduction at the cathode, the standard
cell potential can be calculated from the standard reduction potentials of
the two half-reactions involved in the overall reaction by using the equation:
E cell E cathode – E anode > 0
But remember both the E cathode and E anode values are shown as reduction
potentials, used directly from the table without reversing.
Once you have calculated the standard cell potential, then the reaction can be
written by reversing the half-reaction associated with the anode (show it as oxidation)
and adding the two half-reactions.
Don’t forget that the number of electrons lost must equal the number of electrons
gained. If they are not equal, use appropriate multipliers to ensure that
they are equal.
Calculate the potential of a cell using the following half-cells:
Ni2 2 e l Ni(s) E 0.25 V
Ag e l Ag(s) E 0.80 V
First, calculate the cell potential using:
E cell E cathode E anode > 0
Since the cell potential must be positive (a galvanic cell) there is only one
arrangement of 0.25 and 0.80 V than can result in a positive value:
Ecell 0.80 V (0.25 V) 1.05 V
This means that the Ni electrode is the anode and is involved in oxidation.
Therefore, we reverse the reduction half-reaction involving Ni, changing the