The reaction below is allowed to come to equilibrium at a given temperature. After equilibrium is reached, some NO₂ gas is added to the container. Which statement below describes a change that will be observed as the system returns to an equilibrium state at the same temperature?

NO₂Cl (g) + NO (g) ⇄ NOCl (g) + NO₂ (g)

Answer: Le Chatlier Principle

Explanation: Le Chatlier Principle states that if stress is being applied to an equilibrium, the reaction would move in hat direction in which the stress is been relaxed.

Thus the given reaction is

NO₂Cl (g) + NO (g) ⇄ NOCl (g) + NO₂ (g)

When equilibrium is reached, some NO₂ gas is added to the container, now there will occur a change which will disturb the equilibrium, We can observe that the NO₂ is the one of the product constituent, thus addition of the same should have shifted to the equilibrium in forward direction. In order to nullify this, the equilibrium will shift in backward reaction.

Thus the equilibrium will shift in backward direction as the system returns to an equilibrium state at the same temperature.