Question

Ferrous sulphate when heated decomposes with the evolution of gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.
A. \[2FeS{{O}_{4}}\xrightarrow{\Delta }F{{e}_{2}}{{O}_{3}}+\text{ }S{{O}_{2}}+\text{ }S{{O}_{3}}\], Displacement reaction
B. \[2FeS{{O}_{4}}\xrightarrow{\Delta }F{{e}_{2}}{{O}_{3}}+\text{ }S{{O}_{2}}\], Decomposition reaction
C. \[2FeS{{O}_{4}}\xrightarrow{\Delta }F{{e}_{2}}{{O}_{3}}+\text{ 2}S{{O}_{2}}\], Displacement reaction
D. \[2FeS{{O}_{4}}\xrightarrow{\Delta }F{{e}_{2}}{{O}_{3}}+\text{ }S{{O}_{2}}+\text{ }S{{O}_{3}}\], Decomposition reaction

Answer 1

Hint: We should first carefully read the question. As the question says, ferrous sulphate decomposes when heated and gives a gas with sulphur in it. It is an endothermic reaction as it involves absorption of heat.

Step by step answer:
We should know that a decomposition reaction is a type of chemical reaction in which a single compound breaks down into two or more elements or new compounds. These reactions often involve an energy source such as heat, light, or electricity that breaks apart the bonds of compounds.
We know that ferrous sulphate is green in colour. When we heat ferrous sulphate, it undergoes decomposition that it breaks into two or more than two products on absorption of energy.
Ferrous sulphate crystals contain water molecules (\[FeS{{O}_{4}}.7{{H}_{2}}O\]). When we heat ferrous sulphate crystals, they lose water and anhydrous ferrous sulphate (\[FeS{{O}_{4}}\]) is formed. So their colour changes from light green to white.
On further heating, anhydrous ferrous sulphate decomposes to form ferric oxide (\[F{{e}_{2}}{{O}_{3}}\]), sulphur dioxide\[(S{{O}_{2}}\]) and sulphur trioxide (\[S{{O}_{3}}\] ). So, the gas emitted smells like burning sulphur. In this reaction, the single reactant \[FeS{{O}_{4}}\]decomposes to form three different products. So, the reaction is a decomposition reaction.
\[2FeS{{O}_{4}}\left( s \right)\xrightarrow{\Delta }F{{e}_{2}}{{O}_{3}}\left( s \right)\text{+ }S{{O}_{2}}\left( g \right)+S{{O}_{3}}\left( g \right)\]
So, from the reaction we came to know that our correct answer is option D. Because, in option D, there is decomposition of ferrous sulphate. And in this option, sulphur dioxide and trioxide is produced by decomposition of ferrous sulphate.

Note: We should know about the term pyrolysis. Pyrolysis is the chemical decomposition of a compound caused by temperatures above $250 – 300^{o}$C is commonly known as pyrolysis. The decomposition takes place because chemical bonds have limited thermal stability and can break due to heat. This type of decomposition usually leads to the formation of smaller molecules.