Displacement reactions

 

Displacement reactions

Displacement reactions are chemical reactions where a metal and a compound with another metal react.

These compounds with metals and non-metals are salts. For example, iron (a metal) and copper sulfate (a salt with copper) react.

In a displacement reaction, a more reactive metal takes the place of a less reactive metal in its compound.

A metal and a salt with the same metal do not react. For example, iron and iron chloride (a salt) do not react.

 

Below is an example of a displacement reaction between iron and copper sulfate:

 

Iron displaces copper in copper sulfate

 

In this example, we can say that the iron (Fe) displaced copper (Cu), as it has swapped positions with copper. Iron is now bonded to the sulfate (SO4) to form iron sulfate (FeSO4), while the metal in the solution has become copper, which is now on its own.

The word equation for this reaction is:

Iron + Copper sulfate → Iron sulfate + Copper

These reactions take place due to differences in reactivity. Let’s take a look at the reactivity series:

 

 

The reactivity series with carbon

 

For a displacement reaction to take place, the element on its own must be more reactive than the element that is in the compound.

In the previous example, iron is more reactive than copper, so it can take its place in a compound. When iron is put in a solution of copper sulfate (CuSO4), it displaces the copper and forms iron sulfate (FeSO4).

This means:

iron dissolves and makes a new solution with sulfate copper comes out of the solution and covers the iron as a solid.

 

Let’s look at an example that wouldn’t work:

 

Iron + Magnesium sulfate →
Fe + MgSO4 →

 

As iron is more reactive than magnesium, it won’t displace magnesium, and therefore the reaction won’t occur.

 

 

What happens in a displacement reaction?

A displacement reaction occurs when a more reactive metal is placed in a solution of a metal salt that contains a less reactive metal. The more reactive metal takes the place of the less reactive metal in the compound, and the less reactive metal is released.

In this process:

 

• the more reactive metal gradually disappears as it forms a new compound in the solution.
• the less reactive metal appears as a solid coating on the surface of the more reactive metal as it is separated from its compound.

 

🧪 Knowledge Check: Displacement Reactions

Test your understanding of the rules governing displacement reactions and the reactivity of metals.

1. In a displacement reaction, which type of metal can take the place of another in a compound?

• A less reactive metal
• A more reactive metal
• Any metal, regardless of reactivity

2. If magnesium is added to copper sulfate solution, what are the resulting products?

• Magnesium sulfate and copper
• Copper magnesium and sulfur
• No reaction occurs

3. Which of the following combinations will result in NO reaction?

• Zinc added to iron sulfate
• Iron added to magnesium sulfate
• Magnesium added to zinc sulfate

4. What is the general rule for metals higher up in the reactivity series?

• They are easily displaced by metals below them.
• They can displace any metal below them in the series.
• They only react with copper compounds.

5. In the reaction Magnesium + Copper Sulfate → Magnesium Sulfate + Copper, what has happened to the copper?

• It has been displaced from the solution.
• It has become more reactive than magnesium.
• It has evaporated into the air.

Click to Reveal Answers

1. A more reactive metal (It has the power to push out the weaker one).
2. Magnesium sulfate and copper (The magnesium takes the sulfate part for itself).
3. Iron added to magnesium sulfate (Iron is lower in the reactivity series than magnesium).
4. They can displace any metal below them (Reactivity increases as you go up the series).
5. It has been displaced (It is left as a solid metal after being forced out of the compound).

 

 

Summary:

 

• A more reactive metal can take the place of a less reactive metal in its compound. This is called a displacement reaction.
• The reactivity series is a list of metals from the most reactive to the least reactive. It can help us to know which displacement reactions will happen.
• We can do some experiments to see how metals react with each other and make a reactivity series from the results.