Question

When lead nitrate is heated, it breaks down into lead monoxide, nitrogen dioxide and oxygen.
$2Pb{{\left( N{{O}_{3}} \right)}_{2}}\to 2PbO+4N{{O}_{2}}+{{O}_{2}}$
The reaction is an example of
(A) Combination reaction
(B) Decomposition reaction
(C) Double decomposition reaction
(D) Displacement reaction

Answer 1

Hint: If a compound is complex in nature, it breaks down into simpler compounds. Lead nitrate is a compound which can easily break down into lead oxide, nitrogen dioxide and oxygen. Thus we see that the above reaction is simply a reaction regarding the breaking down of a molecule into simpler molecules leading to various products from 1 single reactant.

Complete step by step solution:
-To be able to answer the above question, we must be familiar with all the types of reactions that occur in nature. There are various ways of classification of reactions. Based on the energy and stability, reactions can be classified as exothermic and endothermic. Based on the feasibility, reactions can be classified as feasible and infeasible reactions.
-Reactions are classified on the basis of the reactant and product structure. On that basis, they are classified as combination reactions, single displacement reactions, double displacement reactions, decomposition reactions, redox reactions and neutralization reactions.
-Reactions in which 2 or more simple compounds or molecules or elements react to give a single compound are called combination reactions. In this, all the reactants combine together to give a single product.
The characteristic equation for this reaction can be denoted as
\[A+B\to AB\]
Eg. \[2{{H}_{2}}+{{O}_{2}}\to 2{{H}_{2}}O\]
Here, 2 simpler molecules combine to give a complex molecule.
-Reactions opposite to this are called decomposition reactions. In this, a complex compound is broken down into 2 or more simple molecules or compounds or elements. The characteristic equation for this reaction is $AB\to A+B$
Eg. $2{{H}_{2}}O\to 2{{H}_{2}}+{{O}_{2}}$
-There are certain types of reactions in which an atom or ion is replaced by another atom/ion of a different compound. Such reactions are called single displacement reactions. In this, the atom or group of atoms detaches itself from a molecule and combines with the other atom/molecule. Its characteristic equation can be shown as
$\begin{align}
& A+BC\to AB+C \\
& \text{or} \\
& \text{A+BC}\to \text{AC+B} \\
\end{align}$
Eg $Zn+2HCl\to ZnC{{l}_{2}}+{{H}_{2}}$
-Reactions in which 2 or more compounds have different ions and all the ions of all the compounds are interchanged with one another. Such types of reactions are called double displacement reactions. Their characteristic equation can be shown as
\[\begin{align}
& AB+CD\to AC+BD \\
& or \\
& AB+CD\to AD+BC \\
\end{align}\]
Eg. $AgN{{O}_{3}}+NaCl\to AgCl+NaN{{O}_{3}}$
-Reactions of acids and bases that result in the formation of salts and water as products are called neutralization reactions. Acids have hydrogen ions and bases have hydride ions which combine to form water. So, the characteristic reaction can be shown as $HA+BOH\to BA+HOH\left( {{H}_{2}}O \right)$
Eg $HCl+NaOH\to {{H}_{2}}O+NaCl$
-Reactions in which one reactant oxidises and one reactant reduces itself are called redox reactions. They occur due to the transfer of electrons from one molecule to another. It is shown in 2 steps- oxidation and reduction
Reduction : ${{A}^{-}}\to A+{{e}^{-}}$
Oxidation : $B+{{e}^{-}}\to {{B}^{-}}$
-Now, seeing the given reaction in the question, we can see that a single reactant is forming different simpler products.
$2Pb{{\left( N{{O}_{3}} \right)}_{2}}\to 2PbO+4N{{O}_{2}}+{{O}_{2}}$
Lead nitrate is a complex compound and it is decomposing itself into simpler compounds.

Therefore, the above reaction is a decomposition reaction and the correct option is (B). Decomposition reaction.

Note: Not all the complex compounds easily decompose to give the products. Sometimes external agents are required to make the reaction feasible such as temperature, pressure, catalysts, etc.
Eg. $CaC{{O}_{3}}\xrightarrow{heat}CaO+C{{O}_{2}}$
This reaction does not occur at room temperature as the reactant is stable at room temperature. The heat has to be applied to complete this reaction.