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

1 Answer
anor277
Feb 9, 2017

Ammonia is a condensable gas..........

Explanation:

...........whereas dinitrogen and dihydrogen are essentially incondensable.

So for the reaction:

#1/2N_2(g) + 3/2H_2(g) rightleftharpoons NH_3(g)#

The small amount of ammonia that is present at equilibrium may be condensed on a cold finger; cf. #"normal b.p."# #NH_3=-33.3# #""^@C#; #"normal b.p."# #N_2=-195.8# #""^@C#; #"normal b.p."# #H_2=-252.9# #""^@C#. The substantial difference in boiling point is about the only thing this reaction has got going for it.

The unreacted, volatile reactant gases may be recycled back thru the reactor, so that the equilibrium may recommence, and good turnovers can be achieved. With each pass thru the reactor, only 5-10% conversions may be achieved, however, removal of the ammonia product drives the equilibrium to the right.

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