A more reactive metal can displace a less reactive metal from its salt solution. The reactivity order is connected to the tendency of metal atoms to form positive ions.
Use the actual pair of metals. Zinc in copper(II) sulfate can form zinc sulfate and copper. Copper in zinc sulfate does not give the reverse displacement under the stated conditions.
At Higher tier, the displacing metal is oxidised by losing electrons. The dissolved metal ion is reduced by gaining electrons. Charge and atoms must both balance.
A balanced equation is necessary but not sufficient. Writing the reverse of a known equation does not establish that the reverse reaction happens spontaneously.
Worked example
Zn + CuSO₄ → ZnSO₄ + Cu. Zinc forms Zn²⁺ while Cu²⁺ forms copper metal.
Zn → Zn²⁺ + 2e⁻ and Cu²⁺ + 2e⁻ → Cu. The spectator sulfate ions do not participate in the net electron transfer.
Specification references
AQA 4.4.1.2 and Higher 4.4.1.4; Edexcel 4.1–4.3, with electron-transfer explanation at Higher tier. These questions use the named solutions at room temperature.
Copy these details if you'd like to report a problem. Your answers and history aren't included. Nothing is sent automatically.
Write an explanation
Critique the claim “Copper will displace zinc because the zinc–copper equation can be written backwards.”
Compare your explanation with the points below. The text you type isn't marked, saved or sent anywhere.
Compare with the example
Check your explanation for
Separate conservation from chemical feasibility.
Use the reactivity ordering.
Explain the direction supported by evidence.
Example answer
The reversed equation could conserve atoms without describing the observed chemistry. Zinc is above copper in the supplied reactivity order, so zinc displaces copper ions. Copper does not displace zinc ions under these conditions.
An answer to improve
Any balanced equation is a possible reaction in either direction.
Improve your answer
Replace an unsupported generalisation with the named substances, conditions and evidence. Add the causal link that your first explanation omitted.
Save your progress
Your progress stays in this browser. Turn on saving if you want to keep it when you leave the page.