Video: Identifying the Change That Would Increase the Amount of N₂(g) Given the Equilibrium Equation for the Decomposition of N₂O(g)

In the given reaction, which of the following would increase the amount of N₂ (g) in the system? 2N₂O (g) ⇌ 2N₂ (g) + O₂ (g) + energy [A] Adding O₂ (g) to the system [B] Adding an inert gas [C] Increasing the temperature at constant pressure [D] Increasing the pressure of the system at constant temperature [E] Adding some N₂O (g).

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Video Transcript

In the given reaction, which of the following would increase the amount of N₂ gas in the system? 2N₂O gas in equilibrium with 2N₂ gas plus O₂ gas plus energy. A) Adding O₂ gas to the system. B) Adding an inert gas. C) Increasing the temperature at constant pressure. D) Increasing the pressure of the system at constant temperature. Or E) Adding some N₂O gas.

Because the reaction we’re given is in equilibrium, we’re going to use Le Chatelier’s principle to answer this question. Le Chatelier’s principle states that, for a system that’s in dynamic equilibrium, if the conditions change, the position of equilibrium will shift to counteract the change. You can think of a system as being in equilibrium like a balanced scale. If we do something that disrupts that balance, like adding more of a product or reactant or changing one of the conditions, the position of equilibrium will shift in a way that restores balance.

We’re looking for some kind of change that will increase the amount of N₂ gas in the system. So let’s look through each of our answer choices to figure out which one will cause this change. Our first answer choice is adding O₂ gas to the system. If we increase the amount of O₂ gas, the position of equilibrium will shift in a way that will decrease the amount of O₂ gas so that equilibrium can be restored.

O₂ gas is a product. So Le Chatelier’s principle tells us that the position of equilibrium will shift to the left towards the reactants to counteract the addition of O₂ gas. This would have the opposite effect of we’re looking for. Adding O₂ gas to the system would decrease the amount of N₂ gas.

Our next answer choice is adding an inert gas. Since the inert gas doesn’t participate in this equilibrium reaction, adding an inert gas would have no effect on the position of equilibrium. So adding an inert gas wouldn’t increase the amount of N₂ gas in the system.

The next answer choice is increasing the temperature of the system at a constant pressure. In the forward direction, this chemical reaction produces energy. When energy is produced as a result of a chemical reaction, that has the effect of increasing the temperature. So because the reaction produces energy, which will increase the temperature. If we increase the temperature that the reaction is occurring at, the position of equilibrium will shift to the left to counteract that change. Increasing the temperature will have the effect of shifting the equilibrium towards the reactants, which will decrease the amount of N₂ gas in the system. So answer choice C isn’t correct.

Answer choice D is increasing the pressure of the system at constant temperature. If the pressure is increased, the position of equilibrium will shift so that the pressure can decrease. The pressure of the system can be decreased if there are fewer moles of gas present. In other words, the position of equilibrium will shift towards the side that has fewer molecules of gas.

On our reactant side, we have two molecules of gas. But on our products, we have a total of three gas molecules. So if the pressure is increased, the position of equilibrium will shift towards the reactants because there’s fewer moles of gas on the reactant side. So increasing the pressure would also decrease the amount of N₂ gas in the system, not increase it.

This leaves us with answer choice E, which is adding some N₂O gas. N₂O gas is a reactant in this reaction. So according to Le Chatelier’s principle, the position of equilibrium will shift in a way that will decrease the concentration of N₂O gas so that equilibrium can be restored, which would be accomplished by shifting the position of equilibrium towards the products. And since N₂ gas is a product, adding some N₂O gas will increase the amount of N₂ gas in the system.

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