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How does cooling the gases allow ammonia to be separated from unused hydrogen and nitrogen, and state what happens to these unused gases?

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Last updated date: 25th Jun 2024
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Answer
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Hint: The ammonia gas is a condensable gas. A condensable gas is the gas the vapours of which upon cooling get added to the liquid. Non-condensable gases do not condense on cooling.

Complete step by step answer:
Ammonia is produced through a process called Haber process. It is also known as Haber-Bosch process. Two German chemists, Fritz Haber and Carl Bosch, have successfully developed a method for the synthesis of ammonia.
For this the nitrogen present in the atmosphere is utilized to generate ammonia gas. The reaction was carried out at high temperature and pressure with nitrogen gas and hydrogen gas in presence of a metal catalyst. The reaction is exothermic in nature with release of heat energy.
${N_2}(g) + 3{H_2}(g) \to 2N{H_3}(g),\Delta H = - 92KJ/mol$
The answer to the given question lies on the effect of cooling on different gases. In general heavier gases or gases which are made of heavier molecules are condensed on cooling and lighter gases or gases with lower molecular weights do not condense upon cooling.
In this regard the ammonia gas is a heavier gas and is a condensable gas while methane, ethane, hydrogen or nitrogen is non-condensable gas. As ammonia is obtained in the form of condensed liquid so it is easier to separate it from hydrogen and nitrogen.
The unreacted and volatile gases (hydrogen and nitrogen) are recycled back through the reactor. Thus the equilibrium is disturbed as the concentration of the reactant gases in the chamber increases which leads to precede the reaction in the forward direction.
Further the removal of the ammonia gas derives the equilibrium of the reaction in the right hand side according to Le Chatelier’s principle.

Note:
The huge difference of boiling points between ammonia and nitrogen and hydrogen gas enables the successful condensation of the ammonia gas rather than hydrogen and nitrogen gas. The recycling of the unreacted starting material allows the reaction to yield good amounts of product formation.