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Decomposition Reactions

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Decomposition reactions occur when complex chemical compounds break down into smaller components. Decomposition reactions often require energy input. The chemical breakdown of hydrogen peroxide to water and oxygen, and the breakdown of water to hydrogen and oxygen, are some common examples of Decomposition Reactions. Hence, a decomposition reaction can simply be defined as a chemical reaction in which one reactant decomposed into two or more products. Let’s understand more concepts like What is a decomposition reaction, Examples, Types, Double Decomposition Reactions, Uses, and FAQs on them, in this article!

What is a Decomposition Reaction?

A decomposition reaction is a chemical process in which the molecule or reactant breakdown into simpler products. Thus, when one reactant breaks down into two or more products, which can be represented by the following equation:

AB → A + B 

In the above reaction, AB represents the reactant which is a chemical compound of A and B that starts the reaction, while A and B represent the products obtained by the reaction. and the arrow represents the direction in which the reaction occurs.

The decomposition reaction is just the opposite of the combination reaction. In a combination reaction, a substance is formed as a result of a chemical combination however, in a decomposition reaction, the substance breaks into new substances.

The process of decomposition requires heat hence, it is also named a thermal decomposition reaction. The energy required for breaking down of product can be in the form of heat, light, or electricity. The electrolysis process is an excellent example of a decomposition reaction. The reaction takes place by breaking down molecules by passing electricity.

H2O ⇢ 2H2+ O2

Decomposition Reaction Examples 

Here are some important examples of Decomposition Reaction:

Decomposition Reaction of Hydrogen Peroxide

Hydrogen peroxide breaks down into water and oxygen in the presence of light, as shown below:

Decomposition Reaction of Hydrogen Peroxide

 

Decomposition Reaction of Metal Carbonates

When metal carbonates are heated, it gets decomposed into their metal oxides and carbon dioxide. For Example, Calcium carbonate get decomposed to Calcium oxide and Carbon Dioxide while, Sodium Carbonate get decomposed to Sodium oxide and Carbon Dioxide, as shown below:

Decomposition Reaction of Metal Carbonates

 

Decomposition Reaction of Metal Hydroxides 

On heating, metal hydroxides break down into metal oxides and water. Thus, Water and sodium oxide are produced during the breakdown of sodium hydroxide, as shown below:

Decomposition Reaction of Metal Hydroxides

 

Decomposition Reaction of Oxy Acids

The decomposition of oxy acids leads to the production of carbon dioxide and water as shown below:

Decomposition Reaction of Oxy Acids

 

Double Decomposition Reaction

A double decomposition reaction is a reaction between two compounds in which components of each substance are exchanged out to create two new compounds. 

A double replacement reaction is a reaction between two compounds in which the positive ion of one molecule is exchanged for the positive ion of the other component. One or more of the reactants in a double decomposition reaction are insoluble in the solvent, which is a type of double displacement reaction. 

For example, zinc chloride and hydrogen sulphide gas are produced when zinc sulphide and hydrochloric acid react. There, zinc sulphide is both solid and undissolved in an aqueous medium.

Double Decomposition Reaction

 

Types of Decomposition Reaction

The decomposition reactions are majorly classified into three types:

  1. Thermal decomposition reaction
  2. Electrolytic decomposition reaction
  3. Photo decomposition reaction

Thermal Decomposition Reaction (Thermolysis)

A single substance can split into two or more simple substances when heated in a chemical process known as thermal decomposition. Since heat is necessary to break the substance’s bonds, the reaction is usually endothermic.

For example, zinc chloride and hydrogen sulphide gas are produced when zinc sulphide and hydrochloric acid react. There, zinc sulphide is both solid and undissolved in an aqueous medium, as shown below:

Thermal Decomposition of potassium chlorate

 

Electrolytic Decomposition Reaction (Electrolysis)

When an electric current is passed through an aqueous solution of a substance, electrolytic decomposition may occur. Water electrolysis works as a good example for Electrolytic Decomposition Reaction (shown below).

Electrolytic Decomposition of Water

 

Photo Decomposition Reaction

Photo decomposition is a chemical reaction in which a chemical compound is splits up into simple substances by exposure to light (photons). 

For example, when a small amount of silver chloride (AgCl) is taken in a watch glass and expose it to the sun for a while. The crystals gradually start to turn grey. Analysis reveals that silver chloride has broken down into silver and chlorine due to sunshine as shown below:

Photo Decomposition of Silver Chloride

 

Decomposition Reaction in our Body

A chemical reaction is a process of changing one substance into another. Living bodies also depend on these reactions for proper functioning, nutrients gaining, digestion, growth, etc. When we see the functioning of our body everything depends on chemical reactions. Digestion is the process of breaking down molecules or food into simpler forms. The salivary glands secret a special chemical substance called enzyme which helps in the breakdown. The starch of food decomposes into glucose in the body.

The reactant or organic food item consisting of carbohydrates, fats, and proteins is broken down into simpler products, and energy is also released. These products are carried throughout the body through the bloodstream for the functioning of the body.

Glucose + Oxygen ⇢ Carbon dioxide + Water + Heat

or

C6H12O6 (aq) + 6O2 (g) ⇢ 6CO2 (g) + 6H2O (l) + Heat

Similarly, proteins are decomposed into simpler forms called amino acids which promote growth. Proteins are broken down into amino acids through hydrolysis. The amino acids are produced to dissolve in blood and are carried out throughout the tissues of the body.

Uses of Decomposition Reactions

  • Decomposition reactions are widely used to extract the metal.
  • Decomposition reactions helps to manufacture cement or calcium oxide.
  • The decomposition reaction cause the fizz in a soda bottle.
  • This reaction is very helpful to break down hazardous waste.
  • Also, it is important for the human digestive system to digest food.

FAQs on Decomposition Reaction

Question 1: Why are Decomposition Reactions called the opposite of Combination Reactions?

Answer:

The decomposition reaction is just the opposite of the combination reaction. In a combination reaction, a substance is formed as a result of a chemical combination however, in a decomposition reaction, the substance breaks into new substances.

Question 2: Are all Decomposition Reactions Endothermic?

Answer:

Yes, almost all decomposition reactions required heat to breakdown, therefore are endothermic in nature. 

Question 3: State important uses of Decomposition Reaction.

Answer:

The following are some of the important uses of Decomposition Reaction:

  • Decomposition reactions are widely used to extract the metal.
  • The decomposition reaction cause the fizz in a soda bottle.
  • This reaction is very helpful to break down hazardous waste.
  • Also it is important in the human digestive system to digest the food.

Question 4: What is an Electrolytic Decomposition Reaction?

Answer:

When an electric electric current is passed through an aqueous solution of a substance, electrolytic decomposition may occur. Water electrolysis works as a good example for Electrolytic Decomposition Reaction.

Question 5: What is a Double Decomposition Reaction?

Answer:

A double replacement reaction is a reaction between two compounds in which the positive ion of one molecule is exchanged for the positive ion of the other component. One or more of the reactants in a double decomposition reaction are insoluble in the solvent, which is a type of double displacement reaction. 

For example, zinc chloride and hydrogen sulphide gas are produced when zinc sulphide and hydrochloric acid react. There, zinc sulphide is both solid and undissolved in an aqueous medium.

Question 5: What is a Thermal Decomposition Reaction?

Answer:

When a single substance split into two or more simple substances when heated in a chemical process known as thermal decomposition. Since heat is necessary to break the substance’s bonds, the reaction is usually endothermic.

Question 6: What is the difference between Combination and Decomposition Reactions?

Answer:

The major difference between Combination and Decomposition Reaction is that in a combination reaction, the reactants combine to form the product. However, in a decomposition reaction, one reactant can form two or more products by the breakage of bonds.

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Last Updated : 08 Nov, 2022
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