🎓 Prepared by students from Boğaziçi University

What are Single Displacement Reactions?

Single displacement reactions occur when one element replaces another element in a compound. They follow the pattern A + BC → AC + B. These reactions depend on the activity series, which ranks elements by their tendency to lose electrons.

Short answer

A single displacement reaction involves one element replacing another in a compound: A + BC → AC + B. Only a more active element can displace a less active one. Example: Fe + CuSO₄ → FeSO₄ + Cu (iron displaces copper).

Single Displacement: Element Replaces Element in Compound

Before

•Element A (more active)
•Compound BC (B is less active)

After

•New compound AC (A and C bonded)
•Released element B (free)

Step-by-step worked examples

Iron (Fe) reacts with copper sulfate (CuSO₄). Iron is more active than copper, so it displaces it. Write and balance.

Unbalanced: Fe + CuSO₄ → FeSO₄ + Cu
Fe: 1 on each side ✓
Cu: 1 on each side ✓
S: 1 on each side ✓
O: 4 on each side ✓
Balanced: Fe + CuSO₄ → FeSO₄ + Cu

Zinc (Zn) is more active than hydrogen. When Zn reacts with HCl, Zn displaces H. Write the balanced equation.

Unbalanced: Zn + HCl → ZnCl₂ + H₂
Zn: 1 on each side ✓
H: 1 on left, 2 on right (unbalanced)
Cl: 1 on left, 2 on right (unbalanced)
Balance: need 2 HCl on left, 1 H₂ on right
Balanced: Zn + 2HCl → ZnCl₂ + H₂

Magnesium (Mg) is more active than zinc. When Mg reacts with ZnCl₂, Mg displaces Zn. Balance this.

Unbalanced: Mg + ZnCl₂ → MgCl₂ + Zn
Mg: 1 on each side ✓
Zn: 1 on each side ✓
Cl: 2 on each side ✓
Balanced: Mg + ZnCl₂ → MgCl₂ + Zn

Flashcards

Quick quiz

Q1.Which equation shows single displacement?

Correct answer: B. Zn + HCl → ZnCl₂ + H₂ shows Zn replacing H in the compound.

Q2.In A + BC → AC + B, what happens?

Correct answer: C. Element A is more active and displaces element B from compound BC.

Q3.Can copper displace hydrogen from HCl?

Correct answer: B. Hydrogen is more active than copper in the activity series.

Q4.In Fe + CuSO₄ → FeSO₄ + Cu, why does Fe displace Cu?

Correct answer: B. Iron is higher in the activity series than copper, so it can displace it.

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Common mistakes

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Any element can displace any other. — Correct: Only a more active element can displace a less active one (by activity series).

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Single displacement has one product. — Correct: Single displacement has two products: a new compound and a free element.

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The activity series is random. — Correct: The activity series ranks elements by their tendency to lose electrons — more active elements are higher.

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Copper can displace iron. — Correct: No, iron is more active. Iron can displace copper, but not the reverse.

FAQ

What is single displacement?

Single displacement is when one element replaces another in a compound: A + BC → AC + B.

Why do only active elements displace?

More active elements have a greater tendency to lose electrons and form bonds, so they can replace less active elements.

What is the activity series?

The activity series ranks elements by their tendency to lose electrons. More active elements (higher on the list) can displace less active ones.

Give an example of single displacement.

Zinc reacting with hydrochloric acid: Zn + 2HCl → ZnCl₂ + H₂. Zinc displaces hydrogen.