Question

What is the major use of Dihydrogen$\left({\mathrm{H}}_2\right)$?

• A. Formation of ${\mathrm{HNO}}_3$.
• B. Synthesis of ammonia$\left({\mathrm{NH}}_3\right)$
• C. Fuel cell for generating electrical energy
• D. Reduction of Heavy metal oxides to metal.

Answer 1

The correct option is B

Synthesis of ammonia$\left({\mathrm{NH}}_3\right)$

Explanation of correct option:

(B) Synthesis of Ammonia$\left({\mathrm{NH}}_3\right)$.

• The major use of Dihydrogen is in the synthesis of Ammonia $\left({\mathrm{NH}}_3\right)$ in Haber's process.
• In Haber's process, nitrogen combines with dihydrogen to form ammonia in the presence of iron as catalyst and Molybdenum as a promoter.
• The balanced chemical reaction can be represented as:
• $\underset{\mathrm{Nitrogen}}{{\mathrm{N}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Hydrogen}}{3{\mathrm{H}}_2\left(\mathrm{g}\right)}\underset{150-200\mathrm{bar},\mathrm{Mo}}{\overset{723\mathrm{K}-773\mathrm{K},\mathrm{Fe}}{\rightleftharpoons }}\underset{\mathrm{Ammonia}}{2{\mathrm{NH}}_3\left(\mathrm{g}\right)}$
  

Explanation of incorrect options:

(A) Formation of ${\mathrm{HNO}}_3$

• In the formation of Nitric acid Dihydrogen is not used.
• Water is used in the synthesis of Nitric acid$\left({\mathrm{HNO}}_3\right)$.
• The reaction of the Synthesis of Nitric acid can be written as:
  $\underset{\mathrm{Nitrogen}\mathrm{dioxide}}{3{\mathrm{NO}}_2\left(\mathrm{g}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\to \underset{\mathrm{Nitric}\mathrm{acid}}{2{\mathrm{HNO}}_3\left(\mathrm{l}\right)}+\underset{\mathrm{Nitric}\mathrm{oxide}}{\mathrm{NO}\left(\mathrm{g}\right)}$

(C) Fuel cell for generating electricity

• Hydrogen in fuel cells has a maximum capacity for generating electricity that is $1volt$ .
• So on a large scale, Dihydrogen is not used in fuel cells for generating electricity.

(D) Reduction of heavy metals oxides to metals

• The dihydrogen gas is used for the reduction of only those heavy metals which are less reactive than hydrogen-like Copper(Cu), Silver(Ag), and Mercury(Hg)

Hence, the correct option is (C).