Question

Thermal decomposition of lead nitrate result in the emission of brown fumes and a residue is left behind when the activity gets over.
i) State the reaction that takes place in the above mentioned activity in the form of a balanced chemical equation.

ii) Identify the brown fumes and residue giving their chemical names.

Answer 1

2 Pb(NO)3)2------->2PbO + 4 NO2 + O2

Answer 2

Answer: i. Decomposition , $2Pb(NO_3)_2(s)\rightarrow PbO(s)+4NO_2(g)+O_2(g)$

ii. Brown fumes - Nitrogen dioxide

Residue - Lead Oxide

Explanation:

Decomposition is a type of chemical reaction in which one reactant gives two or more than two products.

$A\rightarrow B+C$

According to the law of conservation of mass, mass can neither be created nor be destroyed. Thus the mass of products has to be equal to the mass of reactants. The number of atoms of each element has to be same on reactant and product side. Thus chemical equations are balanced.

The balanced chemical equation for decomposition of lead nitrate:

$2Pb(NO_3)_2(s)\rightarrow 2PbO(s)+4NO_2(g)+O_2(g)$

The brown fumes are of $NO_2$ which is nitrogen dioxide and the residue is $PbO$ which is lead oxide.