Question

Consider the following equation: $2 SO _2(g)+ O _2(g) \rightleftharpoons 2 SO _3(g), \Delta H =-190 \,kJ$. The number of factors which will increase the yield of $SO _3$ at equilibrium from the following is _______ 
A. Increasing temperature 
B. Increasing pressure 
C. Adding more $SO _2$ 
D. Adding more $O _2$ E Addition of catalyst

Answer 1

Correct Answer: 3

To determine which factors will increase the yield of SO₃ at equilibrium in the given reaction:

2 SO₂(g) + O₂(g) ⇌ 2 SO₃(g), ΔH = -190 kJ

we analyze each option based on Le Chatelier's principle and chemical equilibrium concepts.

1. Increasing temperature: The reaction is exothermic (ΔH is negative), releasing heat. According to Le Chatelier's principle, increasing temperature will favor the endothermic direction (reverse reaction), decreasing the yield of SO₃. This does not increase SO₃ yield.
2. Increasing pressure: The reaction involves a reduction in the number of gas moles (3 moles of reactant form 2 moles of product). Higher pressure will favor the side with fewer moles, thus increasing SO₃ yield. Increases SO₃ yield.
3. Adding more SO₂: Increasing concentration of reactant shifts equilibrium to the right, producing more SO₃. Increases SO₃ yield.
4. Adding more O₂: Similar to adding SO₂, this shifts equilibrium to the right, increasing SO₃ production. Increases SO₃ yield.
5. Addition of catalyst: A catalyst speeds up the attainment of equilibrium but does not shift its position. Therefore, it does not change the yield of SO₃. This does not increase SO₃ yield.

Considering the analysis, 3 factors increase the yield of SO₃:

• Increasing pressure
• Adding SO₂
• Adding O₂

The computed result, 3, is within the provided range (3,3).