Equilibrium: JEE Main Chemistry Question with Solution
Consider the following equation:2SO2(g)+O2(g)⇌2SO3(g),ΔH=−190 kJThe number of factors which will increase the yield of SO3 at equilibrium from the following is
A. Increasing temperature
B. Increasing pressure
C. Adding more SO2
D. Adding more O2
E. Addition of catalyst
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Hint 1 of 4
How does an increase in temperature affect the equilibrium position of this reaction?
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Step-by-step solutionView
Correct answer
Exactly 3 factors (increasing pressure, adding more SO2, and adding more O2) will increase the equilibrium yield of SO3.
Option analysis
Why each option works or fails
Reviewed route
Solution
StepWorking
01given
Reaction: 2SO2(g)+O2(g)⇌2SO3(g), with ΔH=−190 kJ (exothermic, Δng=2−(2+1)=−1). Proposed factors: A (increasing T), B (increasing P), C (adding SO2), D (adding O2), E (adding catalyst).
02find
Count the total number of factors among A, B, C, D, E that shift equilibrium forward and increase the yield of SO3.
03strategise
Apply Le Chatelier's principle:
- Exothermic reaction (ΔH<0): Increasing temperature favors the endothermic (backward) direction, decreasing yield.
- Decrease in moles of gas (Δng<0): Increasing pressure shifts equilibrium toward fewer gaseous moles (forward), increasing yield.
- Adding reactants (extSO2 or extO2): Shifts equilibrium forward to consume reactants, increasing yield.
- Addition of catalyst: Increases the rate of both forward and backward reactions equally; does not alter equilibrium yield or position.
04execute
Evaluating each option:
- A: False (decreases yield)
- B: True (shifts forward)
- C: True (shifts forward)
- D: True (shifts forward)
- E: False (no effect on equilibrium yield)
Total valid factors = 3 (B, C, D).
✓verify
Catalysts only affect kinetics (rate), not thermodynamics/equilibrium yield. Increasing T of an exothermic process lowers K_eq. B, C, D clearly shift the system to the right. The count is exactly 3.
Hints that build this answer step by step
How does an increase in temperature affect the equilibrium position of this reaction?
It shifts the equilibrium to the left, decreasing the yield of SO3.
How does increasing the total pressure affect the yield of SO3?
It increases the yield because the forward reaction produces fewer moles of gas (3 moles → 2 moles).
What effect do adding reactants (SO2 or O2) and adding a catalyst have on the equilibrium yield?
Adding reactants increases the yield of SO3, while a catalyst has no effect on equilibrium yield.
Counting all the factors listed (A through E), how many increase the yield of SO3 at equilibrium?
Does adding a catalyst increase the yield of product formed at equilibrium?
No, a catalyst speeds up the approach to equilibrium. It lowers the activation energy equally for both forward and reverse paths. Therefore, it does not change the equilibrium constant or the equilibrium composition.