Question

What are the possible uses of dihydrogen ($H_2$) gas?

Answer 1

HINT: Think of the chemical properties of dihydrogen gas (for instance good reducing agent, reactivity with oxides, calorific value etc) and now think very carefully about what its possible uses could be.

Complete step-by-step solution -

$H_2$ is one of the most essential gases of the atmosphere, and it has many possible uses, some of which include:

● It is used as a reducing agent for experimental and industrial purposes. In metallurgical processes, it is used to reduce heavy metal oxides to metals. However, it can only reduce those oxides in which reactivity of the metal is lesser than that of Hydrogen (For eg. Cu, Ag, Hg etc).
 $AgO\text{ + }H_2\text{ }\to \text{ }Ag\text{ + }H_2O$
● It is used in the manufacture of vanaspati fat oils like soybean, cotton seeds etc.
● The most important use of dihydrogen is in the mass manufacturing of ammonia by Haber process which is carried out in the presence of Fe catalyst with temperature between 450 – $500^o$C with the pressure at about 150 – 200 bar.

$3H_2\text{ + $N_2$ }\xrightarrow[150-200bar]{723-773K,\text{ Fe }}\text{ 2}NH_3$

● It is used in the preparation of many compounds such as metal hydrides, hydrogen chloride, water gas, methanol and fertilizers such as urea etc.
● It is also used as a rocket fuel for space programs and research due to its incredibly high calorific value with $H_2$ possessing Gross Calorific Value (GCV) of 341.

NOTE: This is an incredibly conceptual question and while one could possibly work out its answer if they are familiar enough with its physical and chemical properties, it is advisable to be very clear on these concepts beforehand.