Questions on Chemical Equilibrium
Multiple-Choice Questions: Chemical Equilibrium
1. What is chemical equilibrium?
A) When the reaction stops completely
B) When all reactants are converted to products
C) When the rates of the forward and reverse reactions are equal
D) When the reactants are equal in mass
E) When only products are present
2. At equilibrium, the concentration of reactants and products:
A) Continue changing
B) Are always equal
C) Are always zero
D) Remain constant
E) Become infinite
3. Which symbol represents a reversible reaction reaching equilibrium?
A) →
B) ⇌
C) =
D) ⟶
E) ←
4. In a closed system at equilibrium:
A) Only the forward reaction occurs
B) Both forward and reverse reactions stop
C) The reaction is irreversible
D) No observable changes occur, but molecules still react
E) The system consumes energy continuously
5. What is the equilibrium constant expression for the reaction: aA + bB ⇌ cC + dD?
A) [A]^a[B]^b / [C]^c[D]^d
B) [C]^c[D]^d / [A]^a[B]^b
C) [A][B] / [C][D]
D) [C][D] - [A][B]
E) aA + bB = cC + dD
6. Which of the following does NOT appear in the equilibrium constant expression?
A) Gases
B) Aqueous solutions
C) Solids
D) Products
E) Reactants
7. A reaction with K_eq >> 1 favors:
A) Reactants
B) Equilibrium
C) Products
D) Catalyst
E) Energy
8. If K_eq << 1, the reaction mixture at equilibrium contains mostly:
A) Products
B) Equal amounts of reactants and products
C) Reactants
D) Catalysts
E) Energy
9. Which of the following can disturb a chemical equilibrium?
A) Addition of a catalyst
B) Increasing temperature
C) Keeping volume constant
D) Using an inert gas
E) Measuring pressure
10. According to Le Chatelier’s Principle, increasing the concentration of reactants will:
A) Stop the reaction
B) Shift the equilibrium to the right
C) Shift the equilibrium to the left
D) Have no effect
E) Change the value of K_eq
11. What effect does a catalyst have on equilibrium?
A) Shifts it to the right
B) Shifts it to the left
C) Changes the value of K_eq
D) Speeds up attainment of equilibrium
E) Increases product formation
12. At equilibrium, what is the value of the reaction quotient Q compared to K_eq?
A) Q > K_eq
B) Q < K_eq
C) Q = K_eq
D) Q = 0
E) Q is undefined
13. In an exothermic reaction, increasing the temperature will:
A) Shift equilibrium to the right
B) Shift equilibrium to the left
C) Not affect equilibrium
D) Increase K_eq
E) Turn the reaction endothermic
14. The equilibrium constant depends on:
A) Catalyst
B) Temperature
C) Pressure
D) Volume
E) Surface area
15. For the reaction N₂ + 3H₂ ⇌ 2NH₃, decreasing the pressure will shift the equilibrium:
A) To the right
B) To the left
C) No effect
D) Toward ammonia
E) Toward equilibrium
16. Which statement is true about equilibrium in a chemical reaction?
A) The reaction has stopped
B) The forward reaction is faster
C) The system is dynamic
D) Only reverse reactions occur
E) The pressure always increases
17. What happens to the equilibrium position if the product is continuously removed?
A) It remains unchanged
B) It shifts to the left
C) It shifts to the right
D) The reverse reaction speeds up
E) The value of K_eq decreases
18. Which condition is required for a chemical system to reach equilibrium?
A) Open container
B) Constant temperature and closed system
C) Low pressure
D) High catalyst concentration
E) Rapid stirring
19. If Q > K_eq, then the system:
A) Is at equilibrium
B) Will form more products
C) Will form more reactants
D) Has too many reactants
E) Stops reacting
20. If the forward and reverse reactions occur at different rates, the system is:
A) At equilibrium
B) Not at equilibrium
C) In dynamic balance
D) Closed
E) A constant-pressure system
Answer Key with Explanations
1. C – At equilibrium, the forward and reverse reaction rates are equal.
2. D – Concentrations remain constant, but not necessarily equal.
3. B – ⇌ represents a reversible reaction at equilibrium.
4. D – At equilibrium, the system appears static but is dynamically active.
5. B – K_eq = [C]^c[D]^d / [A]^a[B]^b for the balanced equation.
6. C – Solids (and liquids) are not included in K_eq expressions.
7. C – A large K_eq (>1) means equilibrium favors products.
8. C – A small K_eq (<1) means equilibrium favors reactants.
9. B – Temperature changes affect equilibrium position.
10. B – Adding reactants shifts equilibrium to form more products.
11. D – A catalyst speeds up both forward and reverse reactions equally, without shifting equilibrium.
12. C – At equilibrium, Q = K_eq.
13. B – For exothermic reactions, increasing temperature shifts equilibrium to the left.
14. B – K_eq is affected only by temperature.
15. B – Decreasing pressure favors the side with more moles of gas (left side here).
16. C – Chemical equilibrium is dynamic, not static.
17. C – Removing product drives the reaction forward (to the right).
18. B – Closed system and constant temperature are essential for equilibrium.
19. C – If Q > K_eq, the system will shift left to form more reactants.
20. B – If rates are not equal, the system is not at equilibrium.
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