Decomposition Reactions – Definition, Classification, Applications, Practice Problems and FAQ

Cakes are the best desserts to have ever existed. What could be a better end to a meal than a piece of cake?

Have you ever wondered how the dough is baked into a fluffy cake? From where does the cake get this fluffy texture?

The special ingredient that makes the cakes fluffy is ‘Baking soda’ (NaHCO3). When the dough mixed with baking soda is kept in an oven and heated, the baking soda decomposed producing sodium bicarbonate, water and carbon dioxide gas. This carbon dioxide gas escapes through the dough and thus making it porous and eventually fluffy. So, to put it in other words, the fluffy cakes we eat are a result of a decomposition reaction.

TABLE OF CONTENTS

• Decomposition Reaction
• Double Decomposition reactions
• Decomposition Reactions – Classification
• Thermochemical Decomposition Reaction
• Electrolytic Decomposition Reaction
• Photo Decomposition Reaction
• Decomposition Reaction – Applications
• Practice Problems
• Frequently Asked Questions – FAQ

Decomposition Reaction

A chemical reaction known as decomposition occurs when one reactant separates into two or more products from one another. It is the opposite of a combination reaction. The atom is replaced with an atom from a different element, for instance, in a displacement reaction. A chemical equation will demonstrate the chemical reaction. It symbolises the transition from reactants to products. The reactant side is represented on the left, and the product side is represented on the right. There are many parenthetical annotations for each chemical, such as those for the terms "solid (s), liquid (l), gas (g), and aqueous" (aq).

The chemical equation for a decomposition reaction takes the following form

A(aq)+B(g)C(s)+D(aq)

The conversion of hydrogen peroxide into oxygen and hydrogen gas is a decomposition reaction.

H₂O₂H₂(g)+O₂(g)

Double Decomposition reactions

Double decomposition reactions are a type of double displacement reaction in which one or more reactants are insoluble in the solvent. However, this term was frequently used to refer to an older version of double displacement reactions.

As an illustration, the reaction between zinc sulphide and hydrochloric acid results in zinc chloride and hydrogen sulphide gas. There, in an aqueous medium, zinc sulphide is both solid and undissolved.

ZnS(s)+2HCl(aq)ZnCl₂(aq)+H₂S(g)

Decomposition Reactions – Classification

There are three types of decomposition reactions.

Thermolysis: Thermolysis is the term for heat-induced breakdown.

Electrolysis: Electrolysis is the process of decomposing through electricity.

Photolysis: Photolysis is the term for light-induced decomposition.

1. Thermochemical Decomposition Reaction

Heat-induced chemical reaction in which one material splits into two or more compounds is called a thermochemical decomposition reaction. This heat is necessary to dissolve the chemical link between the components. It is an endothermic process.

1. Calcium Carbonate Decomposition Reaction

In the heat, limestone or calcium breaks down into calcium oxide, sometimes known as quicklime, and CO₂.

CaCO₃(s)+HeatCaO(s)+CO₂(g)

2. Potassium Chlorate Decomposition Reaction

During heating, potassium chlorate breaks down into potassium chloride and oxygen. The process is used to create oxygen. The decomposition is carried out with manganese dioxide acting as a catalyst present.

3. Hydrated Oxalic Acid Decomposition Reaction

In the presence of heat, hydrated oxalic acid breaks down into oxalic acid and water. Heat converts H2C2O4.2H2O to H2C2O4 and 2H2O.

H₂C₂O₄.2H₂O+HeatH₂C₂O₂+2H₂O

2. Electrolytic Decomposition Reaction

Aqueous solutions of a substance are exposed to an electric current during this reaction. For instance, water electrolysis.

2H₂O(l)2H₂(g)+O₂(g)

Reaction of Sodium Chloride Decomposition

Molten sodium chloride is transformed into sodium and chlorine when electricity is passed to it.

2NaCl(s)2Na(s)+Cl₂(g)

3. Photo Decomposition Reaction

In the presence of sunshine, this process takes place.

The reaction of Silver Chloride Decomposition

The colour of the crystal changes to grey when a tiny amount of AgCl is added to a watch glass. Silver chloride is transformed into silver using this process.

2AgCl(s)2Ag(s)+Cl₂(g)

The decomposition of carbonates into metal oxide and carbon dioxide following heating is one example of a decomposition reaction.

CaCO₃(s)CaO(s)+CO₂(g)

Na₂CO₃(s)Na₂O(s)+CO₂(g)

Decomposition Reaction – Applications

1. It is utilised to extract the metal.

2. It facilitates the production of cement.

3. It aids in providing indigestion relief.

4. It is employed in the decomposition of silver chloride into silver.

5. Thermite welding is another application for it.

6. Breaking the bonds of a chemical involves reactions including light, heat, and electricity.

7. A reaction of decomposition is what causes the fizz in a soda bottle.

8. It's a component in the production of quicklime.

Practice Problems

1. Which of the following is a decomposition reaction?

1. 3H₂(g)+N₂(g)2NH₃(g)
2. Na₂O(s)+CO₂(g)Na₂CO₃(s)
3. 2HCl(s)H₂(g)+Cl₂(g)
4. MgO(s)+H₂O(l)Mg(OH)₂(aq)

Answer: C
A chemical reaction known as decomposition occurs when one reactant separates into two or more products from one another. It is the opposite of a combination reaction. The reactions given in options A, B and D are examples of combination reactions as products in these reactions are obtained by the combination of the reactants. But in the reaction given in option C, the reactant decomposes to give the products. Therefore, it is an example of a decomposition reaction.

So, option C is the correct answer.

2. Which of the following are types of decomposition reactions?

1. Thermite Decomposition Reaction
2. Pyrolysis Decomposition Reaction
3. Pericyclic Decomposition Reaction
4. Photo Decomposition Reaction

Answer: D
There are three types of decomposition reactions, Thermochemical decomposition reactions, Electrolytic decomposition reactions and Photo decomposition reactions.

So, option D is the correct answer.

3. Which of the following is decomposition reaction?

1. Zn(s)+FeSO₄(aq)Fe(s)+ZnSO₄(aq)
2. 4Al(s)+3O₂(g)2Al₂O₃(s)
3. NH₄Cl(g)NH₃(g)+HCl(g)
4. NO(g)+O₂(g)NO₂(g)

Answer:
A chemical reaction known as decomposition occurs when one reactant separates into two or more products from one another. It is the opposite of a combination reaction. The reactions given in options B and D are examples of combination reactions as products in these reactions are obtained by the combination of the reactants. The reaction given in option A is a displacement reaction. But in the reaction given in option C, the reactant decomposes to give the products. Therefore, it is an example of a decomposition reaction.

So, option C is the correct answer.

4. Which of the following statements is incorrect for decomposition reactions?

1. Thermochemical decomposition reactions are those which need light for the reaction to take place.
2. Electrolytic decomposition reactions are those which need heat for the reaction to take place.
3. Photo decomposition reactions are those which need light for the reaction to take place.
4. Thermochemical decomposition reactions are those which need electricity for the reaction to take place.

Answer: D
Thermochemical decomposition reactions, Electrolytic decomposition reactions and Photo decomposition reactions are those which need heat, electricity and light for the reaction to take place, respectively. Hence, the statement given in option D is incorrect.

So, option D is the correct answer.

Frequently Asked Questions – FAQ

1. Are all processes involving decomposition endothermic?
Answer: No, not all decomposition processes involve heat transfer. Both endothermic and exothermic reactions can take place during decomposition. The latter is more typical than the former, though.

2. What are some uses for decomposition reactions?
Answer: The extraction of metals from their ores is one of the significant uses of decomposition processes. For instance, by putting calamine through a decomposition reaction, zinc can be extracted. The same process can be used to make sodium from sodium chloride (NaCl).

3. Describe the double decomposition reaction.
Answer: A double decomposition reaction is a sort of decomposition process in which two constituent reactants exchange positive and negative ions to create two new molecules.

4. Is decomposition a physical or chemical process?
Answer: Decomposition involves the breakdown of a chemical compound into smaller molecules. Therefore it is a chemical process rather than a physical process.

5. Why is hydrogen peroxide stored in dark bottles?
Answer: Hydrogen peroxide is susceptible to decomposition when exposed to light. This phenomenon is called photodecomposition. To avoid this, hydrogen peroxide is stored in dark bottles or containers.

6. Does pH affect decomposition reaction?
Answer: The decomposition of a compound increases with temperature and pH. pH is one of the factors that affect decomposition reaction. For instance, the pH at which hydrogen peroxide is optimally stable is 4.5. When the pH is increased above 5, the decomposition increases exponentially.

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