Questions on Le Châtelier's Principle
Multiple-Choice Questions: Le Châtelier's Principle
1. What does Le Châtelier’s Principle state?
A) Equilibrium favors the side with fewer moles
B) When a stress is applied to a system at equilibrium, the system shifts to oppose the stress
C) The concentration of products is always greater than reactants
D) A catalyst changes the equilibrium position
E) The equilibrium constant increases with temperature
2. Which of the following is considered a "stress" on a system at equilibrium?
A) Changing catalyst
B) Adding more product or reactant
C) Keeping temperature constant
D) Decreasing volume in a solid
E) Adding inert gas at constant volume
3. What will happen if more reactant is added to a system at equilibrium?
A) The equilibrium constant decreases
B) The system shifts to the left
C) The system shifts to the right
D) The system stops reacting
E) No change occurs
4. For the reaction: N₂ + 3H₂ ⇌ 2NH₃, what happens if H₂ is removed?
A) The reaction shifts to the right
B) The equilibrium remains unchanged
C) The reaction shifts to the left
D) The pressure increases
E) K_eq increases
5. In the reaction: 2SO₂ + O₂ ⇌ 2SO₃, what happens if pressure is increased?
A) Reaction shifts to the right
B) Reaction shifts to the left
C) No change
D) Reaction stops
E) K_eq becomes zero
6. If temperature is increased for an exothermic reaction at equilibrium, the system will:
A) Shift toward the products
B) Shift toward the reactants
C) Stay the same
D) Form a precipitate
E) Decompose the reactants
7. What effect does a catalyst have on equilibrium position?
A) Shifts it to the right
B) Shifts it to the left
C) Increases product formation
D) No effect
E) Increases K_eq
8. In a gaseous reaction with unequal moles, decreasing the volume will shift equilibrium:
A) To the side with more moles
B) To the side with fewer moles
C) To the side with liquids
D) To the side with inert gases
E) Not at all
9. For an endothermic reaction, increasing temperature will:
A) Favor the reactants
B) Stop the reaction
C) Favor the products
D) Decrease rate
E) Precipitate solids
10. Which change will NOT shift the position of equilibrium?
A) Change in temperature
B) Change in pressure (for gases)
C) Addition of a catalyst
D) Addition of more reactant
E) Removal of product
11. In the reaction: A + B ⇌ C + D, removing product C will:
A) Shift the reaction to the left
B) Shift the reaction to the right
C) Stop the reaction
D) Decrease K_eq
E) Produce more reactant
12. Le Châtelier's Principle applies to systems that are:
A) Closed and at equilibrium
B) Open and dynamic
C) Always irreversible
D) Static and balanced
E) Catalyzed reactions only
13. In an exothermic reaction, what happens when temperature is decreased?
A) Shift left
B) Shift right
C) No change
D) K_eq decreases
E) Catalyst is deactivated
14. Which of the following would cause a shift in equilibrium for a gaseous reaction?
A) Adding an inert gas at constant volume
B) Adding an inert gas at constant pressure
C) Adding a catalyst
D) Increasing particle size
E) Removing catalyst
15. Which of the following increases the rate of reaching equilibrium but doesn’t shift the equilibrium?
A) Increasing concentration
B) Removing product
C) Adding catalyst
D) Increasing temperature
E) Changing volume
16. In a reaction where Δn (moles of gas) = 0, what is the effect of pressure change on equilibrium?
A) Shifts left
B) Shifts right
C) No effect
D) Reaction reverses
E) Catalyst is needed
17. If temperature is increased and the equilibrium shifts right, the reaction is:
A) Exothermic
B) Endothermic
C) Irreversible
D) Not temperature dependent
E) Catalytic
18. What happens if both products are removed in a reaction at equilibrium?
A) Shift left
B) No change
C) Shift right
D) K_eq decreases
E) Reaction stops
19. In the reaction: CaCO₃(s) ⇌ CaO(s) + CO₂(g), what will happen if CO₂ is removed?
A) Shift left
B) No change
C) Shift right
D) Decrease temperature
E) K_eq becomes 1
20. Which factor is not considered when applying Le Châtelier’s Principle?
A) Temperature
B) Concentration
C) Pressure (for gases)
D) Catalyst
E) Volume (for gases)
- Questions on Chemical Equilibrium
- Questions on Equilibrium Constant (K_eq) and Calculations
- Questions on Nonreversible Reactions
Answer Key with Explanations
1. B – Le Châtelier’s Principle explains how a system opposes stress to restore equilibrium.
2. B – Changing concentration is a common stress that shifts equilibrium.
3. C – Adding reactant causes the system to shift right (form more products).
4. C – Removing H₂ shifts the equilibrium left to replace the removed reactant.
5. A – Increasing pressure shifts equilibrium to the side with fewer gas moles (2 vs 3).
6. B – For exothermic reactions, heat is a "product", so increasing temperature shifts left.
7. D – A catalyst does not affect equilibrium position, only speeds up reaching it.
8. B – Decreasing volume increases pressure and shifts equilibrium to the side with fewer moles.
9. C – Endothermic reactions absorb heat; more heat favors the products.
10. C – A catalyst has no effect on the equilibrium position.
11. B – Removing a product shifts the reaction right to produce more product.
12. A – Le Châtelier’s Principle applies to closed systems at equilibrium.
13. B – Decreasing temperature in an exothermic reaction shifts right (heat is "removed").
14. B – Adding an inert gas at constant pressure increases volume, decreasing pressure and shifting equilibrium.
15. C – A catalyst speeds up the forward and reverse rates equally but doesn’t affect the position.
16. C – If Δn = 0, pressure changes have no effect on equilibrium.
17. B – If heat causes a shift to products, the reaction is endothermic.
18. C – Removing products always shifts equilibrium right.
19. C – Removing CO₂ drives the reaction forward to replace it.
20. D – Catalysts do not affect equilibrium and are not part of Le Châtelier’s analysis.
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