Displacement Reactions

Equations and Reaction Types

What is a displacement reaction?

A reaction in which one element replaces another element in a compound.

What happens in a metal displacement reaction?

A more reactive metal displaces a less reactive metal from its compound.

What determines whether one metal can displace another?

Their relative reactivities.

Can a less reactive metal displace a more reactive metal from its compound?

No.

What are the products of a typical metal displacement reaction?

A different metal and a different metal compound.

Are displacement reactions redox reactions?

Yes.

Why are displacement reactions redox reactions?

Electrons are transferred between species.

What does oxidation mean in terms of electrons?

Loss of electrons.

What does reduction mean in terms of electrons?

Gain of electrons.

What is the full equation for magnesium reacting with copper(II) sulfate?

Mg(s) + CuSO₄(aq) → Cu(s) + MgSO₄(aq)

Which metal displaces copper from copper(II) sulfate?

Magnesium.

Why does magnesium displace copper from copper(II) sulfate?

Magnesium is more reactive than copper.

What is the full ionic equation for magnesium reacting with copper(II) sulfate?

Mg(s) + Cu²⁺(aq) + SO₄²⁻(aq) → Cu(s) + Mg²⁺(aq) + SO₄²⁻(aq)

Which ion is the spectator ion when magnesium reacts with copper(II) sulfate?

SO₄²⁻.

What is the simplified ionic equation for magnesium reacting with copper(II) ions?

Mg(s) + Cu²⁺(aq) → Cu(s) + Mg²⁺(aq)

What happens to magnesium atoms during this reaction?

They lose electrons and form Mg²⁺ ions.

Is magnesium oxidised or reduced when it displaces copper?

Oxidised.

What happens to Cu²⁺ ions during this reaction?

They gain electrons and form copper atoms.

Are Cu²⁺ ions oxidised or reduced?

Reduced.

In Mg + Cu²⁺ → Cu + Mg²⁺, which species loses electrons?

Mg.

In Mg + Cu²⁺ → Cu + Mg²⁺, which species gains electrons?

Cu²⁺.

Where are electrons transferred in the magnesium–copper displacement reaction?

From magnesium atoms to Cu²⁺ ions.

What colour is copper(II) sulfate solution?

Blue.

What happens to the blue colour when magnesium is added to copper(II) sulfate solution?

It becomes paler.

What happens if excess magnesium is added to copper(II) sulfate solution?

The solution becomes colourless as magnesium sulfate forms.

What visible change occurs to magnesium during its reaction with copper(II) sulfate?

It changes from silvery to brown as copper forms on its surface.

What causes the brown coating on magnesium in copper(II) sulfate solution?

Solid copper being deposited.

What is the equation for aluminium reacting with iron(III) oxide?

2Al(s) + Fe₂O₃(s) → 2Fe(s) + Al₂O₃(s)

Which element is displaced from iron(III) oxide in the thermite reaction?

Iron.

Why can aluminium displace iron from iron(III) oxide?

Aluminium is more reactive than iron.

What is the simplified ionic equation for the thermite reaction?

2Al(s) + 2Fe³⁺ → 2Fe + 2Al³⁺

What happens to aluminium in the thermite reaction?

Aluminium loses electrons and is oxidised.

What happens to Fe³⁺ ions in the thermite reaction?

They gain electrons and are reduced.

From which species to which species are electrons transferred in the thermite reaction?

From aluminium atoms to Fe³⁺ ions.

Is the thermite reaction a redox reaction?

Yes.

Does the thermite reaction require energy to start?

Yes, a very high temperature is required.

What type of reaction is the thermite reaction in terms of energy transfer?

Highly exothermic.

What metal is produced in the thermite reaction?

Iron.

What state is the iron initially produced in the thermite reaction?

Molten iron.

What is the thermite reaction used for?

Joining railway rails.

Why is the thermite reaction useful for joining railway rails?

It produces enough heat to form molten iron, which flows into the gap and joins the rails when it cools.

What mixture is used in the thermite process?

Aluminium and iron(III) oxide.

What can be used to ignite the thermite mixture?

A magnesium fuse.

Can displacement reactions occur with halogens?

Yes.

What happens in a halogen displacement reaction?

A more reactive halogen displaces a less reactive halogen from its compound.

Can chlorine displace bromine from a bromide compound?

Yes.

Why can chlorine displace bromine from bromide ions?

Chlorine is more reactive than bromine.

What is the full equation for chlorine reacting with potassium bromide?

Cl₂(aq) + 2KBr(aq) → Br₂(aq) + 2KCl(aq)

What is the full ionic equation for chlorine reacting with potassium bromide?

Cl₂(aq) + 2K⁺(aq) + 2Br⁻(aq) → Br₂(aq) + 2K⁺(aq) + 2Cl⁻(aq)

Which ion is the spectator ion when chlorine reacts with potassium bromide?

K⁺.

What is the simplified ionic equation for chlorine displacing bromine?

Cl₂(aq) + 2Br⁻(aq) → Br₂(aq) + 2Cl⁻(aq)

What happens to bromide ions when they react with chlorine?

They lose electrons and form bromine.

Are bromide ions oxidised or reduced in a chlorine–bromide displacement reaction?

Oxidised.

What happens to chlorine molecules in a reaction with bromide ions?

They gain electrons and form chloride ions.

Is chlorine oxidised or reduced when it reacts with bromide ions?

Reduced.

Where are electrons transferred in the chlorine–bromide reaction?

From bromide ions to chlorine.

Why is a halogen displacement reaction a redox reaction?

One species loses electrons while another gains electrons.

What is the general rule for metal displacement reactions?

A more reactive metal displaces a less reactive metal from its compound.

What is the general rule for halogen displacement reactions?

A more reactive halogen displaces a less reactive halogen from its compound.

How can displacement reactions be used to compare reactivity?

If one element displaces another from its compound, the displacing element is more reactive.

Write the full equation for iron reacting with silver nitrate.

Fe(s) + 2AgNO₃(aq) → 2Ag(s) + Fe(NO₃)₂(aq)

Write the full ionic equation for iron reacting with silver nitrate.

Fe(s) + 2Ag⁺(aq) + 2NO₃⁻(aq) → 2Ag(s) + Fe²⁺(aq) + 2NO₃⁻(aq)

What is the spectator ion when iron reacts with silver nitrate?

NO₃⁻.

Write the simplified ionic equation for iron reacting with silver ions.

Fe(s) + 2Ag⁺(aq) → Fe²⁺(aq) + 2Ag(s)

What happens when zinc and copper(II) oxide are heated together?

Zinc displaces copper from copper(II) oxide.

Write the equation for zinc reacting with copper(II) oxide.

Zn(s) + CuO(s) → ZnO(s) + Cu(s)

Why can zinc displace copper from copper(II) oxide?

Zinc is more reactive than copper.

Which species is oxidised when zinc reacts with copper(II) oxide?

Zinc.

Which species is reduced when zinc reacts with copper(II) oxide?

Cu²⁺ ions in copper(II) oxide.