displacement reaction
Displacement reactions 9-30-2024
L.O:
· Relate ionic and full equations, with state symbols, to observations from simple test-tube reactions, for displacement reactions.
What is a displacement reaction?
A displacement reaction is a type of chemical reaction in which one element is replaced by another element in a compound. This occurs when a more reactive element replaces a less reactive element.
Displacement reactions involving metals
o The reactivity of metals decreases going down the reactivity series which means that a more reactive metal will displace a less reactive metal from its compounds.
o A metal can react with:
ü A metal oxide (by heating) or;
ü an aqueous solution of a metal compound
Example 1: zinc + copper (II) oxide → zinc oxide + copper
Zn + CuO → ZnO + Cu
Example 2: Iron nail + copper (II) chloride → Copper + iron (II) chloride
Fe + CuCl2 → Cu + FeCl2
Metal displacement reactions in aqueous solutions
Let’s take an example of magnesium that is more reactive than copper. It displaces copper from copper sulfate solution:
magnesium + copper sulfate → magnesium sulfate + copper
Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s)
In this displacement reaction:
· magnesium becomes coated with copper
· The magnesium changes in appearance from silvery to brown as copper forms on it.
· the blue colour of the solution becomes paler. If an excess of magnesium is added, the solution becomes colourless, as magnesium sulfate forms.
· Electrons are transferred from magnesium atoms to copper (II) ions, so magnesium atms are oxidized (loss of electron) and copper (II) ions are reduced (gain of electrons). So this is a redox reaction
The ionic equation for this reaction
Mg(s) + Cu2+ (aq) + SO42-(aq) → Cu(s) + Mg2+ (aq) + SO42-(aq)
Canceling the spectator ions: Mg(s) + Cu2+ (aq) + → Cu(s) + Mg2+ (aq)
Metal displacement reactions in the solid state
o Thermite method: an exothermic reaction which is for reducing metallic oxides using finely divided aluminum powder.
o The mixture of aluminum and the oxide (Fe2O3) is ignited, causing the aluminum to be
oxidized and the metal oxide to be reduced to the metal which causes it to release a large amount of energy.
o It is so exothermic that the iron is formed as a molten metal which flows into the gap between the two rails. The molten iron cools, joining the rails together.
2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
The ionic equation for this reaction
2Al(l) + 2Fe3+(l) + 3O2-(l) → 2Fe(l) + 2Al3+(l) + 3O2-(l)
2Al(l) + 2Fe3+(l) → 2Fe(l) + 2Al3+(l)
o Electrons are transferred from aluminum atoms to iron (III) ions, so aluminum atoms are oxidised (loss of electrons) and iron (III) are reduced (gain of electrons), so this is a redox reaction.
Displacement reactions involving Halogens
o A halogen displacement reaction occurs when a more reactive halogen displaces a less reactive halogen from an aqueous solution of its halide
o The reactivity of Group VII non-metals increases as you move up the group
o Out of the three commonly used halogens, chlorine, bromine and iodine, chlorine is the most reactive and iodine is the least reactive
o Example: Chlorine will displace Bromine from a potassium bromide solution.
The ionic equation for this reaction
Cl2(aq) + 2KBr(aq) → Br2(aq)+2KCl (aq)
Cl2(aq) + 2K+(aq) + 2Br-(aq) → Br2(aq)+ 2K+(aq) + 2Cl- (aq)
Cl2(aq) + 2Br-(aq) → Br2(aq) + 2Cl- (aq)
o As with the metal displacement reactions, this is a redox reaction. Electrons are transferred from bromide ions to chlorine, so bromide ions are oxidised (loss of electrons) and chlorine is reduced (gain of electrons).