Will NH3 decompose into N2 and H2?

Question

In chemical kinetics , we learn that in a reversible reaction ,both the forward reaction and reverse reaction occur at the same time. At equilibrium , the rates are the same. For example:Production of ammonia NH3 .During the production of ammonia both the forward & reverse reaction is present .

$\ce{ 3H_2(g) + N_2(g) ⟶ 2NH_3(g)}$ forward reaction

$\ce{2NH_3(g) ⟶ 3H_2(g) + N_2(g)}$ reverse reaction

Now come to the Gibbs free energy.

Under standard condition(298K) , it can be calculated that the reaction is forwardly favored (forward reaction is spontaneous,and thus the decomposition of NH3 is non-spontaneous). I understand H2 and N2 will produce more NH3.My question is at this situation will NH3 decompose into H2 and N2 to some extent(though it is a non-spontaneous process)?.But chemical kinetics tells that both reaction(not necessarily same rate) have to be present to create equilibrium in future .

Answer 1

Under standard conditions (100kPa, 0°C), nitrogen and hydrogen do not react with each other in any measurable way. It follows logically that also ammonia cannot decompose (as it would to a small extent in an equillibrium reaction), because otherwise it would decompose completely with time, although it is stable.

In equillibrium, the forward and backward reaction rates must be identical and finite.

Answer 2

In equilibrium, as you say, forward and backward reactions have same velocity of conversion (that is equilibrium). Out of equilibrium, you could probably see that the non-spontaneous direction of the process has a very small rate.

Microscopically, a molecule of product can collide another molecule absorbing its energy, and then -because of the high energy- be converted in a reactant. Following your example, a very small quantity of $\ce{NH3}$ produced will be converted into a reactant. In short: it is improbable but occurs.