When hydrogen gas is added to the following reaction,

The reaction will proceed to wards the right to regain the equilibrium.

Explanation:

The given problem can be better understand by using the Le chatelier principle.

This principle states that when the equilibrium of system is disturbed the the system shifts the equilibrium to overcome this change and regain the equilibrium.

Equilibrium:

This is the state of reaction in which the rate of forward reaction and reverse reaction are same.

There are three factors that effect the equilibrium condition.

The change in concentration

The change in volume

The change in temperature

In given equilibrium reaction,

3H₂ + N₂  ⇄  2NH₃

when amount of H₂ is increased it means more amount of reactants are on left side and equilibrium is disturb. Thus equilibrium is shifted toward the right produces more ammonia and regain the equilibrium.