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Question Video: Determining How Adding More of a Reactant Will Effect the Position of Equilibrium Chemistry • 10th Grade

Sulfur trioxide is produced as part of the process of manufacturing sulfuric acid as shown: 2 SO₂ (g) + O₂ (g) ⇌ 2 SO₃ (g), △𝐻 = −196 kJ/mol. What effect will adding more oxygen have on the position of the equilibrium?

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Video Transcript

Sulfur trioxide is produced as part of the process of manufacturing sulfuric acid as shown: two SO2 gas plus O2 gas in equilibrium with two SO3 gas. △𝐻 for this reaction is negative 196 kilojoules per mole. What effect will adding more oxygen have on the position of the equilibrium? (A) The equilibrium will not move. (B) The equilibrium will move to the right. (C) The equilibrium will move to the left.

If we want to understand what effect some change will have on the position of an equilibrium, we should refer to Le Chatelier’s principle. Le Chatelier’s principle states that for a dynamic equilibrium, if the conditions change, the position of equilibrium will move to counteract the change.

In this question, the conditions that changes is that more oxygen is added. To counteract this change, the position of equilibrium will move to decrease the amount of oxygen. We’ll use this diagram to help us visualize this change. We start off with an equilibrium mixture of the three gases participating in the reaction. When more oxygen is added, the system is no longer in equilibrium. This also means that more oxygen gas is available to react with sulfur dioxide. When the excess oxygen gas has reacted to form more sulfur trioxide, a new equilibrium will be established.

Comparing this new equilibrium system to the original one, we can see that there are now more products present. So we can say the position of equilibrium has moved towards the products as a result of adding more oxygen. Since the products are on the right-hand side of the equation, we’ll often say the position of equilibrium has moved to the right when the new equilibrium favors the products. So answer choice (B) is the correct answer to this question. The effect that adding more oxygen will have on the position of the equilibrium is the equilibrium will move to the right.

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