Final answer:
Iron is more reactive than nickel because it ranks higher in the activity series and can replace elements below it, such as copper, while nickel cannot replace iron. Iron's multiple oxidation states and its reactivity demonstrated in reactions add to its higher reactivity over nickel.
Step-by-step explanation:
The reactivity of metals like iron (Fe) and nickel (Ni) can be explained by the activity series, which ranks metals based on their tendency to undergo single-replacement reactions. Iron is higher up in the activity series compared to nickel, meaning it is more reactive and can replace elements below it in the series. For example, when nickel reacts with iron (III) nitrate, no reaction occurs because nickel cannot replace the more reactive iron in the compound.
Furthermore, iron's reactivity can be understood by considering oxidation numbers. For instance, in FeO, iron has an oxidation number of +2. The reactivity of iron is also influenced by its ability to take on multiple oxidation states, making it more versatile in reactions compared to nickel.
A specific reaction demonstrates the reactivity difference as well:
Fe+CuSO4 → FeSO4 + Cu. In this reaction, iron replaces copper in the sulfate compound, oxidizing from zero to +2, while copper reduces from +2 to 0. This reflects iron's higher position relative to copper in the activity series, similarly helping us understand why iron is more reactive than nickel.