WAEC 2015 Chemistry · Question 7

Consider the following equilibrium system: 2SO2(g) + O2(g) 2SO3(g) The addition of more O2(g) to the system…

Question

Consider the following equilibrium system: 2SO2(g) + O2(g) $\rightleftharpoons$ 2SO3(g) The addition of more O2(g) to the system will shift the equilibrium position to the

A.Right leading to the production of more SO3(g)
B.Right leading to the production of more SO2(g)
C.Left leading to the production of more SO2(g)
D.Left leading to the production of more SO3(g)

Answer: A. Right leading to the production of more SO3(g)

Explanation written with AI and checked against the answer key

1. Analyze the question We have the equilibrium 2SO₂(g) + O₂(g) ⇌ 2SO₃(g). More O₂, a reactant, is added. We must decide which way the equilibrium shifts and what is produced.

2. Concept: Le Chatelier's Principle When a system at equilibrium is disturbed, it shifts in the direction that opposes the change.

Adding a reactant shifts the equilibrium to the side that uses up that reactant, which is the product side (right).
Removing a reactant shifts it to the left.

3. Solution

O₂ is on the left (reactant side), and adding more increases its concentration.
The system tries to reduce the extra O₂ by consuming it.
O₂ is consumed when it reacts with SO₂ to form SO₃, so the forward reaction is favoured.
The equilibrium shifts to the right.
The result is more SO₃ and less SO₂ (SO₂ is used up).

Checking the options:

A: Right, more SO₃ ✔
B: Right, more SO₂ ✘ (SO₂ is consumed, not produced)
C: Left, more SO₂ ✘ (the shift is not to the left)
D: Left, more SO₃ ✘ (a left shift cannot produce more SO₃)

4. Answer: A

5. Exam tip Think "reactant added, go right; product added, go left". Always check that the direction and the substance produced are consistent. A right shift means more product (SO₃), and a left shift means more reactants. Options B and D are inconsistent in this way, so you can eliminate them immediately.

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