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A displacement reaction is where a more reactive element takes the place of a less reactive element in a compound. Free notes and 13 questions answered.
Displacement Reactions and the Extended Reactivity Series is part of Reactivity of metals in GCSE AQA Higher Chemistry.
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A displacement reaction is where a more reactive element takes the place of a less reactive element in a compound. Free notes and 13 questions answered.
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Use this lesson to stay inside Reactivity of metals while connecting the detail back to the wider Topic 4: Chemical changes topic.
Read the core explanations from Displacement Reactions and the Extended Reactivity Series before testing yourself from memory.
Drop a piece of zinc into copper sulphate solution and watch the displacement reaction happen. The blue solution fades, copper appears, and the zinc slowly dissolves as the ions swap places. This is a chemical reaction, not magic - it's a displacement reaction, and it reveals something fundamental about how metals compete for electrons.
Think of it like a queue for the most popular ride at a theme park. The more reactive metals are like the pushier people who can barge to the front. They kick out the less reactive metals from their compounds.
You know the metal reactivity series from potassium down to gold. But here's where it gets interesting - hydrogen and carbon aren't metals, yet they appear in our reactivity series. This extended version is crucial for understanding real-world chemistry.
The Extended Reactivity Series (most to least reactive):Potassium > Sodium > Lithium > Calcium > Magnesium > Aluminium > Carbon > Zinc > Iron > Tin > Lead > Hydrogen > Copper > Silver > Gold > Platinum
Notice carbon sits above zinc, and hydrogen sits above copper. This positioning isn't random - it tells us exactly which metals we can extract using these non-metals as reducing agents.
The golden rule is simple: a more reactive element can displace a less reactive element from its compound. But you need to be careful about what 'more reactive' actually means in the extended series.
Worked example: Predicting if Displacement Will Occur
Will magnesium displace hydrogen from hydrochloric acid?
Answer: Yes, magnesium will displace hydrogen from hydrochloric acid, producing hydrogen gas.
Trap alert: Many students think hydrogen and carbon are 'special cases'. They're not - they follow exactly the same displacement rules as metals. Carbon above zinc means carbon can displace zinc. Hydrogen above copper means hydrogen can displace copper (though this rarely happens in practice).
Displacement reactions aren't just lab curiosities - they're the foundation of how we extract metals from ores and why some metals are more expensive than others.
Metal Extraction: Metals above carbon in the reactivity series (like aluminium) need expensive electrolysis. Metals below carbon (like iron and zinc) can be extracted cheaply using carbon as a reducing agent. This is why aluminium was once more valuable than gold, despite being the most abundant metal in Earth's crust.
Thermite Reactions: Aluminium powder mixed with iron oxide creates a displacement reaction so vigorous it's used to weld railway tracks. The reaction reaches over 2500°C because aluminium is much more reactive than iron.
Exam questions love to combine displacement reactions with mass calculations. The key is getting your balanced equation right first, then using molar ratios.
Worked example: Mass Calculation in Displacement
What mass of copper is produced when 6.5g of zinc displaces copper from copper sulphate solution? [4 marks]
Answer: 6.35g of copper is produced
Displacement questions appear in every GCSE chemistry paper. Here's how to nail them every time.
Common exam mistakes: Writing 'copper is less reactive' instead of 'copper is less reactive than zinc'. Examiners want the comparison made explicit. Also, many students forget that hydrogen and carbon follow the same displacement rules as metals - they're not exceptions.
Exam precision note: In Displacement Reactions and the Extended Reactivity Series - The reactivity series - Reactivity of metals, always identify the key chemical idea first, then link it to evidence, data, or an equation. A high-scoring GCSE answer names the particles involved, states what changes, and justifies the conclusion using correct scientific language. Where calculations are used, show each step with units and keep significant figures sensible. Finally, check that terminology matches AQA wording so your answer is unambiguous and mark-scheme friendly.
In displacement reactions, a more reactive element takes the place of a less reactive element in a compound. Observations depend on the reaction: in a metal-salt displacement the solution colour may change and a new solid may appear, while in an acid reaction a gas may be produced. The reactivity series helps predict which changes will actually happen.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
A displacement reaction is a reaction where a more reactive element takes the place of a less reactive element in a compound. For example, zinc displaces copper from copper sulphate solution: the blue solution fades, copper appears and the zinc dissolves.
The thermite reaction is a displacement reaction in which aluminium powder reacts with iron oxide, reaching over 2500°C because aluminium is much more reactive than iron. It is so vigorous it is used to weld railway tracks.
When zinc is added to copper sulphate solution, a displacement reaction happens: the blue solution fades, copper appears and the zinc slowly dissolves. Zinc is more reactive than copper, so it takes the place of copper in the compound.
Carbon is more reactive than zinc, so it sits higher than zinc in the extended reactivity series. Carbon follows the same displacement rules as metals, so it can displace zinc, which is why zinc and iron can be extracted cheaply using carbon as a reducing agent.
The balanced equation is Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s), with 1 Zn, 1 Cu, 1 S and 4 O on each side. The 1:1 ratio means 6.5g (0.1 mol) of zinc produces 0.1 mol, or 6.35g, of copper.
The observations in a displacement reaction depend on the reaction. In a metal-salt displacement the solution colour may change and a new solid may appear, such as copper appearing as blue copper sulphate fades, while in an acid reaction a gas such as hydrogen may be produced.
In the extended reactivity series, carbon sits between aluminium and zinc, and hydrogen sits between lead and copper. Their positions show which metals carbon can extract as a reducing agent and which metals can displace hydrogen from acids.
A displacement reaction happens only if the free element is more reactive than the element in the compound. For example, magnesium is higher than hydrogen in the reactivity series, so it displaces hydrogen from hydrochloric acid: Mg + 2HCl → MgCl₂ + H₂.
6.5g of zinc produces 6.35g of copper in Zn + CuSO₄ → ZnSO₄ + Cu. The moles of zinc are 6.5 ÷ 65 = 0.1 mol, the ratio is 1:1, so the mass of copper = 0.1 × 63.5 = 6.35g.
The extended reactivity series adds the non-metals carbon and hydrogen to the metals: potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, tin, lead, hydrogen, copper, silver, gold, platinum. Their positions show which metals carbon and hydrogen can displace.
Magnesium can displace hydrogen from hydrochloric acid because magnesium is higher than hydrogen in the reactivity series. The equation is Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g), and bubbling shows hydrogen gas is produced.
Aluminium was once more valuable than gold, despite being the most abundant metal in Earth's crust, because it is more reactive than carbon. It can't be extracted cheaply using carbon, so it needs expensive electrolysis.
Hydrogen can in theory displace copper, because hydrogen sits higher than copper in the extended reactivity series, though this rarely happens in practice. It also explains why copper doesn't react with dilute acids: copper is less reactive than hydrogen.