Question

Justify that the following reaction is redox reaction: $2NH_{3}(g)+5O_{2}(g)\longrightarrow 4NO(g)+6H_{2}O(g)$

Answer 1

Step 1: Write the reaction along with oxidation number of each element that is present in the reactants as well as the products of the reaction.

$\begin{matrix}\quad -3\quad+1\quad \quad \quad \quad 0\quad \quad \quad +2\quad -2\quad \quad +1\quad -2 \\ 4N{ H }_{ 3 }(g)+{ 5O }_{ 2 }(g)\longrightarrow 4NO(g)+{ 6H }_{ 2 }O(g) \end{matrix}$            

Step 2: Notice that the oxidation number of nitrogen is -3 in the reactants but it is +2 in the products. So there is an increase in the oxidation number of nitrogen during the chemical reaction. Hence it is evident that $N{ H }_{ 3 }$ is oxidized to NO.

Step 3: Notice that the oxidation number of Oxygen is 0 in the reactants but it is -2 in the products. So there is a decrease in the oxidation number of hydrogen during the chemical reaction. Hence it is evident that  ${ O }_{ 2 }$ is reduced to ${ H }_{ 2 }O$.

Thus it is proved that the given reaction is a redox reaction.