For the reaction N2 (g) + 3H2 (g) 2NH3 (g), what will happen if more nitrogen gas is added?

N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)

Le Chatelier's principle basically states that whatever change we add into a closed system, the system is going to try to undo it---to counteract it.

If we add more N₂ (g), the system will try to reduce that added concentration in the reactants (nitrogen gas is a part of the reactants) by

Shifting the equilibrium to the products (shift to the right)

This results in the following:

The concentration of N₂ (nitrogen) decreases.

The concentration of H₂ (hydrogen) decreases.

The concentration of NH₃ (ammonia) increases.

The reaction will shift toward the products.

Adding more reactant will shift the reaction to the product.