The synthesis of ammonia gives off heat:
(g) +
(g)
H
(298) = -22.1 kcal per 2 moles of
Ammonia molecules absorb heat when they dissociate.
The energy released in forming one NN
and three
HH
bonds is not enough to break apart six NH
bonds in the two ammonia molecules.
Raising the temperature therefore should favor dissociation, because
the extra thermal energy is put to work pulling molecules apart.
This is borne out by the measured values of
for the reaction.
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