JEE MainChemistry

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Applying Le Chatelier's Principle to Exothermic Gas Reactions

Q: 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.

Consider the following equation: 2SO_2(g) + O_2(g) rightleftharpoons 2SO_3(g), ΔH = -190kJ 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

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Correct answer

Exactly 3 factors (increasing pressure, adding more ${SO}_{2}$ , and adding more $O_{2}$ ) will increase the equilibrium yield of ${SO}_{3}$ .

Option analysis

Why each option works or fails

Reviewed route

Solution

StepWorking

01Given

Reaction: $2 {SO}_{2} (g) + O_{2} (g) ⇌ 2 {SO}_{3} (g)$ , with $Δ H = - 190 kJ$ (exothermic, $Δ n_{g} = 2 - (2 + 1) = - 1$ ). Proposed factors: A (increasing T), B (increasing P), C (adding ${SO}_{2}$ ), D (adding $O_{2}$ ), 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 ${SO}_{3}$ .

03Strategise

Apply Le Chatelier's principle: - Exothermic reaction ( $Δ H < 0$ ): Increasing temperature favors the endothermic (backward) direction, decreasing yield. - Decrease in moles of gas ( $Δ n_{g} < 0$ ): Increasing pressure shifts equilibrium toward fewer gaseous moles (forward), increasing yield. - Adding reactants ( $e x t {S O}_{2}$ or $e x t O_{2}$ ): 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 ${SO}_{3}$ .
How does increasing the total pressure affect the yield of ${SO}_{3}$ ?
It increases the yield because the forward reaction produces fewer moles of gas (3 moles $\to$ 2 moles).
What effect do adding reactants ( ${SO}_{2}$ or $O_{2}$ ) and adding a catalyst have on the equilibrium yield?
Adding reactants increases the yield of ${SO}_{3}$ , while a catalyst has no effect on equilibrium yield.
Counting all the factors listed (A through E), how many increase the yield of ${SO}_{3}$ at equilibrium?
3 factors (B, C, and D)

✓ Source and academic review

Question type: Numerical
Exam relevance: JEE Main · Chemistry
Academic status: Answer verified against the official NTA key
Source: Previous-year question
Editorial review: 9 September 2026

Quick checks

Students also ask

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.

Answer

Exactly 3 factors (increasing pressure, adding more ${SO}_{2}$ , and adding more $O_{2}$ ) will increase the equilibrium yield of ${SO}_{3}$ .

Why each option works or fails

Step-by-step solution

Given: Reaction: $2 {SO}_{2} (g) + O_{2} (g) ⇌ 2 {SO}_{3} (g)$ , with $Δ H = - 190 kJ$ (exothermic, $Δ n_{g} = 2 - (2 + 1) = - 1$ ). Proposed factors: A (increasing T), B (increasing P), C (adding ${SO}_{2}$ ), D (adding $O_{2}$ ), E (adding catalyst).
Find: Count the total number of factors among A, B, C, D, E that shift equilibrium forward and increase the yield of ${SO}_{3}$ .
Strategise: Apply Le Chatelier's principle: - Exothermic reaction ( $Δ H < 0$ ): Increasing temperature favors the endothermic (backward) direction, decreasing yield. - Decrease in moles of gas ( $Δ n_{g} < 0$ ): Increasing pressure shifts equilibrium toward fewer gaseous moles (forward), increasing yield. - Adding reactants ( $e x t {S O}_{2}$ or $e x t O_{2}$ ): 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.
Execute: 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.

Applying Le Chatelier's Principle to Exothermic Gas Reactions

What feels right?

Exactly 3 factors (increasing pressure, adding more ${SO}_{2}$ , and adding more $O_{2}$ ) will increase the equilibrium yield of ${SO}_{3}$ .

Why each option works or fails

Solution

01Given

02Find

03Strategise

04Execute

✓Verify

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