Question

A reaction in which a compound breakdown into two or,more simpler substances is

• A. Displacement reaction.
• B. Neutralisation reaction.
• C. Decomposition reaction.
• D. Endothermic reaction.

Answer 1

The correct option is C

Decomposition reaction.

The explanation for the correct answer

Option C

• A decomposition reaction is a type of reaction in which one reactant breakdown into two or more different products.
• Generally, a decomposition reaction is represented as:

$\underset{\mathrm{Reactant}}{\mathrm{AB}}\to \underset{\mathrm{Product}1}{\mathrm{A}}+\underset{\mathrm{Product}2}{\mathrm{B}}$

• Decomposition reaction always requires an input of energy.
• Example: When $\mathrm{Calcium}\mathrm{carbonate}\left({\mathrm{CaCO}}_3\right)$ is heated, it breaks up into $\mathrm{Calcium}\mathrm{oxide}\left(\mathrm{CaO}\right)$ and $\mathrm{Carbon}\mathrm{dioxide}\left({\mathrm{CO}}_2\right)$.

Chemical equation: $\underset{\mathrm{Calcium}\mathrm{carbonate}}{{\mathrm{CaCO}}_3\left(\mathrm{s}\right)}\stackrel{∆}{\to }\underset{\mathrm{Calcium}\mathrm{oxide}}{\mathrm{CaO}\left(\mathrm{s}\right)}+\underset{\mathrm{Carbon}\mathrm{dioxide}}{{\mathrm{CO}}_2\left(\mathrm{g}\right)}$

The explanation for the incorrect answer

Option A

• A displacement reaction is a type of reaction in which more reactive metal displaces less reactive metal from its compound.
• Generally, a displacement reaction is represented as: $\mathrm{AB}+\mathrm{C}\to \mathrm{AC}+\mathrm{B}$
• The basic principle behind the displacement reaction is the reactivity of metals.
• A reactivity series contains a list of metals that are arranged in the decreasing order of their reactivity. This series is helping us to know which metals displace other metals.
• Since $\mathrm{Iron}\left(\mathrm{Fe}\right)$ is more reactive than $\mathrm{Copper}\left(\mathrm{Cu}\right)$. Hence $\mathrm{Iron}\left(\mathrm{Fe}\right)$ displaces $\mathrm{Copper}\left(\mathrm{Cu}\right)$ from a solution of $\mathrm{Copper}\left(\mathrm{II}\right)\mathrm{sulphate}$.

$\underset{\mathrm{Iron}}{\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{Copper}\mathrm{sulphate}}{{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{Ferrous}\mathrm{sulphate}}{{\mathrm{FeSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{Copper}}{\mathrm{Cu}\left(\mathrm{s}\right)}$

Option B

• Neutralisation reaction is a kind of double displacement reaction, in which acid reacts with a base to form salt and water.
• Generally, a neutralization reaction is represented as: $\mathrm{Acid}+\mathrm{Base}\to \mathrm{Salt}+\mathrm{Water}$
• The product salt always contains cation from the base and anion from the acid.
• Example: When a solution of $\mathrm{Sodium}\mathrm{hydroxide}\left(\mathrm{NaOH}\right)$ reacts with $\mathrm{Hydrochloric}\mathrm{acid}\left(\mathrm{HCl}\right)$, salt $\mathrm{Sodium}\mathrm{chloride}\left(\mathrm{NaCl}\right)$ and water(${\mathrm{H}}_2\mathrm{O}$) are formed.

$\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\mathrm{NaOH}\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydrochloric}\mathrm{acid}}{\mathrm{HCl}\left(\mathrm{aq}\right)}\stackrel{}{\to }\underset{\mathrm{Sodium}\mathrm{chloride}}{\mathrm{NaCl}\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}$

Option D

• A chemical reaction that absorbs heat from the surroundings is called an endothermic reaction.
• Example: On heating, $\mathrm{Calcium}\mathrm{carbonate}\left({\mathrm{CaCO}}_3\right)$ decomposed into $\mathrm{Calcium}\mathrm{oxide}\left(\mathrm{CaO}\right)$ and $\mathrm{Carbon}\mathrm{dioxide}\left({\mathrm{CO}}_2\right)$.

Thus, option C i.e., Decomposition reaction is the correct answer.