Displacement Reaction (Single and Double Displacement Reactions)

Displacement reactions are very important chemical reactions of chemistry. They are used in many ways in various fields. For example, we use electroplating to prevent iron objects from rusting which is based on displacement reaction.

Displacement Reaction Definition 

The type of reaction in which part of one reactant is displaced by another reactant is called displacement reaction. It is also called a  replacement reaction. As replacement of one ion of reactant takes place by another ion of reactant. 

Example – $$Fe+CuS{O}_4\to FeS{O}_4+Cu$$

There are two types of displacement reactions –

1. Single displacement reaction 

2. Double displacement reaction 

What is Single Displacement Reaction?

Those reactions in which one element replaces another element from its salt or compound are called single displacement reactions. These are also called single replacement reactions. General representation can be written as well –

A + B-C $$\to$$ A-C + B

It will occur if A is more reactive than B. Generally, metals and their salts give single displacement reactions. In these reactions, more reactive metal displaces less reactive metal from its salt. For example, potassium is more reactive than magnesium, so potassium replaces magnesium from magnesium chloride. The reaction between potassium and magnesium chloride occurs as follows –

$$2K+MgC{l}_2\to 2KCl+Mg$$

What is Reactivity Series? 

Reactivity series is the series of metals based on their reactivity from highest to lowest. So, the reactivity series of metals can be defined as a series of metals, in order of reactivity from highest to lowest. It is also known as activity series. The reactivity of metals is because of their incomplete outer orbitals or due to their electronic configuration. Metals form positively charged ions as they tend to lose electrons. Metals with high atomic numbers tend to be more reactive as their electrons are far from the positively charged nucleus. So, they can be removed easily.

Types of Chemical Reaction

1. Synthesis Reactions

Synthesis reactions happen when two separate atoms or molecules come together to generate a new molecule or substance.

Eg. Water: $$2H_2(g)+O_2(g)\to 2H_{2}O(g)$$

2. Decomposition Reactions

The following are the three main types of breakdown reactions:

1. Reaction of Thermal Decomposition:

A decomposition reaction that is activated by thermal energy is known as a thermal decomposition reaction.

Eg. $$CaC{O}_3\to CaO+C{O}_2$$

Calcium carbonate decomposes into calcium oxide and carbon dioxide when heated. This procedure is used to make quick lime, which is a critical ingredient in a variety of industries. 

2. Reaction of Electrolytic Decomposition:

The activation energy for decomposition in an electrolytic decomposition reaction is delivered in the form of electrical energy. The electrolysis of water is an example of an electrolytic breakdown reaction, which may be represented by the chemical equation:

Eg. $$2H_{2}O\to 2H_2+O_2$$

3. Photo Decomposition/photolytic Breakdown/photochemical Decomposition are all Terms for the same thing:

A photodecomposition reaction is a sort of decomposition process in which the reactant absorbs energy from photons and breaks down into its parts. The breakdown of dioxygen and an oxygen radical, as indicated by the chemical equation below, is an example of a photodecomposition process.

Eg.$$O_3+h\nu \to O_2+O$$.

Replacement Reactions

1. Single-Replacement Reactions

A single replacement reaction, also known as a single displacement reaction, occurs when one element in a molecule is swapped for another.

Eg.$$2K+2H_{2}O\to 2KOH+H$$.

2. Double-Replacement Reactions

When components of two ionic compounds are swapped, two new compounds are formed. Double replacement reactions are also known as double displacement, exchange, or metathesis processes.

Eg. $$BaC{l}_2(aq)+N{a}_{2}S{O}_4(aq)\to BaS{O}_4(s)+2NaCl(aq)$$

Combustion Reactions

A combustion reaction is a type of chemical reaction that involves the interaction of a molecule with an oxidant to create heat and a new product.

Eg. $$C{H}_4+O_2\to C{O}_2+H_{2}O$$.

Uses of Displacement Reaction

1. Welding using Thermite

Railway joints are welded together using an alloy of aluminium (Al) and ferric oxide (Fe2O3).

The following is the reaction:

$$2Al+F{e}_2{O}_3\to A{l}_2{O}_3+2Fe$$

2. Iron Ore Extraction

By reacting with carbon, iron may be removed from its ore.

$$3C+2F{e}_2{O}_3\to 4Fe+3C{O}_2$$

3. Metals are Extracted

Other metals, such as chromium, can be extracted via a displacement reaction.

$$3C+2C{r}_2{O}_3\to 4Cr+3C{O}_2$$

4. Neutralisation of Acids

Indigestion is caused by the production of HCl acid in our stomach. Antacids are made up of a base that causes a displacement response in the body.

$$Mg(OH{)}_2+2HCl\to MgC{l}_2+2H_{2}O$$

Examples of Single Displacement Reaction

1. Reaction between hydrochloric acid and zinc:

$$2HCl(aq)+Zn(s)\to ZnC{l}_2(aq)+H_2(g)$$

2. Reaction between sodium chloride and fluorine:

$$2NaCl(aq)+F_2(g)\to 2NaF(s)+C{l}_2(g)$$

3. Reaction between calcium iodide and chlorine:

$$Ca{I}_2(s)+C{l}_2(g)\to CaC{l}_2(s)+l_2(s)$$ 

4. Reaction between calcium and fluoride and bromine:

$$Ca{F}_2(s)+B{r}_2(\ell )\to CaB{r}_2(s)+F_2(g)$$

Examples of Double Displacement Reaction

1. Reaction between silver nitrate and sodium chloride:

$$AgN{O}_3+NaCl\to AgCl+NaN{O}_3$$

2. Reaction between sodium chloride and calcium sulphate:

$$2NaCl+CaS{O}_4\to N{a}_{2}S{O}_4+CaCl$$.

3. Reaction between sulphuric acid and lithium hydroxide:

$$H_{2}S{O}_4+2LiOH\rightleftarrows Li{O}_{2}S{O}_4+2H_{2}O$$.

4. Reaction between silver nitrate and hydrochloric acid:

$$AgN{O}_3+HCl\rightleftarrows AgCl+HN{O}_3$$.

5. Reaction between lead(II) nitrate and sodium chloride:

$$Pb(N{O}_3{)}_2+2NaCl\rightleftarrows 2NaN{O}_3+PbCl$$.

6. The reaction between hydrochloric acid and sodium hydroxide:

$$HCl+NaOH\to NaCl+H_{2}O$$.

7. The reaction between aluminium sulphate and ammonium hydroxide:

$$A{l}_2(S{O}_4{)}_3+6N{H}_{4}OH\to 2Al(OH{)}_3+3(N{H}_4{)}_{2}SO$$.

Reactivity Series of Metals is given Below

Hydrogen is a non-metal but still, it has been included in the reactivity series as it helps in the comparison of reactivity of metals. 

Examples of Displacement Reactions 

• Examples of single displacement reaction:

• Reaction between zinc and copper sulphate –

$$Zn+CuS{O}_4\to ZnS{O}_4+Cu$$

• Reaction between copper and silver nitrate –

$$Cu+2AgN{O}_3\to CuN{O}_3+2Ag$$

• Reaction between iron and copper sulphate –

$$Fe+CuS{O}_4\to FeS{O}_4+Cu$$

• Reaction between lead and copper chloride –

$$Pb+CuC{l}_2\to PbC{l}_2+Cu$$

• Reaction between chlorine and sodium bromide –

$$C{l}_2+2NaBr\to 2NaCl+B{r}_2$$

Examples of Double Displacement Reaction

• Reaction between potassium nitrate and aluminum chloride –

$$KN{O}_3+AlC{l}_3\to Al(N{O}_3{)}_3+KCl$$

• Reaction between lead nitrate and potassium iodide –

$$Pb(N{O}_3{)}_2+2KI\to 2KN{O}_3+Pb{l}_2$$

• Reaction between iron chloride and barium hydroxide –

$$FeC{l}_3+Ba(OH{)}_2\to Fe(OH{)}_3+BaC{l}_2$$

• Reaction between lead nitrate and sodium sulphate –

$$Pb(N{O}_3{)}_2+N{a}_{2}S{O}_4\to PbS{O}_4+2NaN{O}_3$$

• Reaction between barium chloride and copper sulphate –

$$BaC{l}_2+CuS{O}_4\to BaS{O}_4+CUC{l}_2$$

Applications of Displacement Reactions 

Displacement reactions have many applications in various fields. Some of them are given below –

• It is used in thermite welding. In which aluminium displaces iron from its oxide.

• It is used in steel making. In which carbon displaces iron from its oxide.

• It is largely used in the extraction of metals. 

• It is used in acid indigestion. 

• It is used in flame photometry. 

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