Given the equation representing a system at equilibrium: #N_2(g) + 3H_2(g) rightleftharpoons 2NH_3(g) + "energy"#, what changes occur when the temperature of this system is decreased?

1 Answer
Mar 9, 2017

#"Le Chatelier's principle"# states that when a system at......


#"Le Chatelier's principle states that when a system at....."#
#"equilibrium is subject to an external stress, the equilibrium"#
#"will move so as to oppose the external stress"#.

As I have said before (I am a broken record): #"oppose "!=" counteract"#.

And thus we try to manipulate the following equilibrium:

#N_2(g) + 3H_2(g) rightleftharpoons 2NH_3(g)+Delta#

Should the temperature be decreased, we are in effect removing heat from the reaction. And thus (all things being equal) the equilibrium should move to the right, to restore the lost heat. Of course, under the new reaction conditions, a new equilibrium constant might pertain (we don't really have a way to assess this unless we are given more specifics).

The industrial synthesis of ammonia, which has been INTENSELY STUDIED, is performed at a reasonably elevated temperature (approx. #500-600# #""^@C#) so as to maintain an acceptable rate and turnover of reaction. The ammonia gas, as it is formed, can be removed from the equilibrium on a cold finger, the reactant gases recycled, and thus the equilibrium can be driven to the right. Of course, a catalyst is used to provide an acceptable rate.