Deducing a reactivity order from experimental results

A reactivity order can be worked out by comparing how substances behave in the same test under comparable conditions. A substance that reacts more readily or more vigorously provides evidence that it is more reactive than one that reacts less readily or less vigorously.

For a fair comparison, conditions that affect the observations should be kept similar. For example, when comparing metals in the same acid, the acid concentration, temperature and amount and surface area of each metal should be comparable.

Combining the comparisons

Suppose three metals are tested with the same acid under comparable conditions:

• Metal A produces bubbles rapidly.
• Metal B produces bubbles more slowly.
• Metal C shows no visible reaction during the test.

A reacts more vigorously than B, so the result places A above B. B reacts while C shows no visible reaction, so the result places B above C. Combining the comparisons gives the experimental order:

A > B > C, where $$>$$ means “is more reactive than”.

A lack of visible reaction places C below a substance that does react in that test; it does not prove that C can never react. If two substances both show no visible reaction, that result alone does not establish which is more reactive.

The order should include only substances that can be placed using the evidence given. Do not assume positions for other substances from a full reactivity series when they were not tested.