Electromotive Series
Definition and meaning of Electromotive Series in chemistry.
The electromotive series is an ordered list of metals (and hydrogen) arranged according to their standard electrode potentials, ranked from the most easily oxidized (most reactive) to the least easily oxidized (most noble).
In more detail
Also called the activity series or electrochemical series, it is built by measuring each half-reaction's standard reduction potential (E°) against the standard hydrogen electrode, defined as 0.00 V. Metals near the top have large negative E° values, lose electrons readily, and act as strong reducing agents, while metals near the bottom have positive E° values and resist oxidation. Chemists use the series to predict whether a metal will displace another metal's ions from solution and to determine which electrode serves as the anode versus cathode in a galvanic cell.
Key facts
| Field | Physical Chemistry |
|---|---|
| Also known as | Activity series, electrochemical series |
| Reference point | Standard hydrogen electrode (SHE), E° = 0.00 V |
| Most reactive metal | Lithium, E° = -3.04 V |
Zinc (E° = -0.76 V) sits above copper (E° = +0.34 V) in the series, so a strip of zinc metal placed in a copper(II) sulfate solution displaces copper: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), with zinc oxidized and copper ions reduced.
Frequently asked questions
What does a metal's position in the electromotive series tell you?
Its relative tendency to be oxidized (lose electrons). A metal higher in the series is a stronger reducing agent than one below it.
How does the series predict displacement reactions?
A metal higher in the series will reduce (displace) the cation of any metal listed below it in solution, but not vice versa.