Here’s a set of 60 multiple-choice questions (MCQs) on reversible reactions and dynamic equilibrium, tailored for BISE Gujranwala standards. The questions are categorized into easy, moderate, and tough, with the answers provided at the end.
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### Easy Questions (18 Questions)
1. **What is a reversible reaction?**
- A) A reaction that goes in one direction only.
- B) A reaction that can proceed in both forward and reverse directions.
- C) A reaction that does not reach equilibrium.
- D) A reaction that only occurs at high temperatures.
2. **Which of the following is a characteristic of dynamic equilibrium?**
- A) Reactants are used up completely.
- B) The concentration of reactants and products remains constant.
- C) No reaction occurs.
- D) The reaction stops.
3. **In a reversible reaction, what does the double arrow (↔) indicate?**
- A) The reaction is complete.
- B) The reaction can proceed in both directions.
- C) The reaction is endothermic.
- D) The reaction is exothermic.
4. **Which of the following is NOT a macroscopic characteristic of dynamic equilibrium?**
- A) Constant concentrations of reactants and products.
- B) No change in color or physical state.
- C) Complete conversion of reactants to products.
- D) Constant pressure and temperature.
5. **What does the law of mass action state?**
- A) The speed of a reaction increases with temperature.
- B) At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction.
- C) The concentration of products decreases over time.
- D) Equilibrium can only be achieved in closed systems.
6. **The equilibrium constant (K) is a ratio of:**
- A) Concentrations of products to reactants at equilibrium.
- B) Concentrations of reactants to products at equilibrium.
- C) Mass of products to mass of reactants.
- D) Temperature to pressure.
7. **Which of the following describes the units of the equilibrium constant for the reaction \( aA + bB ⇌ cC + dD \)?**
- A) Moles per liter (mol/L)
- B) Dimensionless
- C) Molarity squared (M²)
- D) Molarity to the power of the sum of products minus reactants (M^c-d)
8. **When the temperature of a system at equilibrium is increased, what is likely to happen?**
- A) The equilibrium will shift towards the reactants.
- B) The equilibrium will shift towards the products.
- C) The equilibrium will not change.
- D) The reaction will stop.
9. **In the equilibrium constant expression \( K_c = \frac{[C]^c[D]^d}{[A]^a[B]^b} \), what do the square brackets represent?**
- A) The physical state of the substances.
- B) The concentration of the substances.
- C) The mass of the substances.
- D) The volume of the substances.
10. **Which of the following reactions is at equilibrium?**
- A) \( 2H_2 + O_2 ⇌ 2H_2O \) where the concentration of reactants and products changes.
- B) \( N_2 + 3H_2 ⇌ 2NH_3 \) with constant concentrations of all substances.
- C) \( H_2 + I_2 ⇌ 2HI \) that produces only products.
- D) \( CH_4 + O_2 ⇌ CO_2 + H_2O \) with no change in concentration.
11. **What effect does a catalyst have on a reversible reaction?**
- A) It shifts the equilibrium towards products.
- B) It increases the rate of both forward and reverse reactions equally.
- C) It changes the equilibrium constant.
- D) It favors the formation of reactants.
12. **Which of the following factors does NOT affect the equilibrium position of a reaction?**
- A) Concentration of reactants.
- B) Temperature.
- C) Pressure.
- D) Presence of light.
13. **What is the equilibrium constant (K) for the reaction \( N_2 + 3H_2 ⇌ 2NH_3 \) at equilibrium?**
- A) \( K = \frac{[NH_3]^2}{[N_2][H_2]^3} \)
- B) \( K = \frac{[N_2][H_2]^3}{[NH_3]^2} \)
- C) \( K = [NH_3]^2 \)
- D) \( K = [N_2][H_2]^3 \)
14. **If the equilibrium constant for a reaction is less than 1, what can be inferred?**
- A) The reactants are favored at equilibrium.
- B) The products are favored at equilibrium.
- C) The reaction does not occur.
- D) The reaction goes to completion.
15. **What is the main importance of the equilibrium constant?**
- A) It tells the speed of the reaction.
- B) It indicates the position of equilibrium.
- C) It shows the physical state of reactants.
- D) It defines the reaction conditions.
16. **Which of the following statements is true regarding an exothermic reaction?**
- A) Increasing temperature shifts the equilibrium to the left.
- B) Increasing temperature shifts the equilibrium to the right.
- C) Decreasing temperature has no effect on equilibrium.
- D) It only produces reactants.
17. **What does it mean if a reaction is described as "endothermic"?**
- A) It releases heat.
- B) It absorbs heat.
- C) It is a spontaneous reaction.
- D) It produces energy.
18. **Which of the following is a characteristic of a saturated solution?**
- A) Contains more solute than it can hold at a given temperature.
- B) Contains less solute than it can hold.
- C) Contains exactly the maximum amount of solute it can hold.
- D) Contains only solid solute.
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### Moderate Questions (24 Questions)
19. **The equilibrium constant expression for the reaction \( 2NO(g) + O_2(g) ⇌ 2NO_2(g) \) is:**
- A) \( K = \frac{[NO_2]^2}{[NO]^2[O_2]} \)
- B) \( K = \frac{[NO]^2[O_2]}{[NO_2]^2} \)
- C) \( K = [NO]^2[O_2]^2 \)
- D) \( K = [NO_2]^2 \)
20. **When an equilibrium mixture is disturbed, it will shift to:**
- A) Minimize the disturbance.
- B) Maximize the concentration of reactants.
- C) Maximize the concentration of products.
- D) Stop all reactions.
21. **What happens to the equilibrium constant if the reaction is reversed?**
- A) It remains the same.
- B) It becomes negative.
- C) It is the reciprocal of the original constant.
- D) It doubles.
22. **For the reaction \( A + B ⇌ C + D \), if \( K = 10 \), which of the following is true?**
- A) Products are favored at equilibrium.
- B) Reactants are favored at equilibrium.
- C) The reaction goes to completion.
- D) No reaction occurs.
23. **In which case is the equilibrium constant affected?**
- A) Changing the concentration of reactants.
- B) Changing the temperature.
- C) Adding a catalyst.
- D) Increasing pressure in a gaseous reaction.
24. **The reaction \( CO(g) + 2H_2(g) ⇌ CH_3OH(g) \) has an equilibrium constant \( K \). If the temperature increases, what will happen to \( K \) if the reaction is exothermic?**
- A) \( K \) increases.
- B) \( K \) decreases.
- C) \( K \) remains unchanged.
- D) \( K \) cannot be determined.
25. **The units of the equilibrium constant \( K_c \) depend on:**
- A) The temperature.
- B) The concentrations of reactants and products.
- C) The specific reaction.
- D) The reaction vessel size.
26. **If the concentration of a product in an equilibrium reaction increases, what will happen to the concentrations of the reactants?**
- A) They will increase.
- B) They will decrease.
- C) They will remain constant.
- D) They will fluctuate wildly.
27. **What does a high value of \( K \) indicate about a reaction?**
- A) The reaction favors the reactants.
- B) The reaction favors the products.
- C) The reaction does not occur.
- D) The reaction reaches equilibrium quickly.
28. **If \( K \) is equal to 1 for a reaction, what can be concluded?**
- A) Reactants and products are present in equal
concentrations at equilibrium.
- B) The reaction does not reach equilibrium.
- C) The products are favored.
- D) The reactants are favored.
29. **When a system at equilibrium is compressed, what will happen?**
- A) It will shift towards the side with more moles of gas.
- B) It will shift towards the side with fewer moles of gas.
- C) It will remain unchanged.
- D) It will only produce reactants.
30. **In the context of dynamic equilibrium, what is "Le Chatelier's Principle"?**
- A) It states that reactions occur only in one direction.
- B) It predicts the behavior of a system when subjected to changes.
- C) It defines the conditions for reaching equilibrium.
- D) It emphasizes the importance of catalysts.
31. **Which of the following is a true statement regarding equilibrium constants?**
- A) They vary with changes in concentration.
- B) They are constant at a given temperature.
- C) They depend on the size of the container.
- D) They are always greater than 1.
32. **Which statement about the equilibrium constant for a reaction is incorrect?**
- A) The units of \( K_c \) can change depending on the reaction.
- B) \( K \) can be calculated from initial concentrations.
- C) \( K \) values are the same for both forward and reverse reactions.
- D) \( K \) values can be determined at any temperature.
33. **How does the addition of an inert gas at constant volume affect the equilibrium?**
- A) It shifts the equilibrium to the right.
- B) It shifts the equilibrium to the left.
- C) It has no effect on the position of equilibrium.
- D) It causes the reaction to stop.
34. **For the reaction \( N_2(g) + 3H_2(g) ⇌ 2NH_3(g) \), if the pressure is increased, what will happen?**
- A) The equilibrium will shift to the right.
- B) The equilibrium will shift to the left.
- C) There will be no effect on equilibrium.
- D) The reaction will stop.
35. **Which of the following does NOT affect the equilibrium position of a reaction?**
- A) Temperature.
- B) Concentration.
- C) Adding a solid reactant.
- D) Pressure changes.
36. **If a reaction reaches equilibrium, what can be inferred about the rates of the forward and reverse reactions?**
- A) The forward reaction rate is greater than the reverse reaction rate.
- B) The reverse reaction rate is greater than the forward reaction rate.
- C) The rates of the forward and reverse reactions are equal.
- D) The reaction is complete.
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### Tough Questions (18 Questions)
37. **In the reaction \( 2A + B ⇌ C + D \), what would happen if the concentration of \( C \) is increased?**
- A) The equilibrium shifts left.
- B) The equilibrium shifts right.
- C) The reaction stops.
- D) The rate of forward reaction decreases.
38. **Calculate the equilibrium constant \( K_c \) for the reaction \( 2SO_2(g) + O_2(g) ⇌ 2SO_3(g) \) given the equilibrium concentrations: [SO2] = 0.5 M, [O2] = 0.3 M, [SO3] = 0.6 M.**
- A) 3.0
- B) 1.5
- C) 2.0
- D) 5.0
39. **For a given reaction, the equilibrium constant \( K \) is given as 0.02. What does this imply?**
- A) Products are favored at equilibrium.
- B) Reactants are favored at equilibrium.
- C) The reaction goes to completion.
- D) The reaction has reached equilibrium.
40. **What would happen to the equilibrium constant if a reaction is conducted at a lower temperature?**
- A) It increases for exothermic reactions.
- B) It decreases for exothermic reactions.
- C) It increases for endothermic reactions.
- D) It remains unchanged.
41. **Which expression is correct for the equilibrium constant \( K_p \) for the reaction \( 2NO(g) + O_2(g) ⇌ 2NO_2(g) \)?**
- A) \( K_p = \frac{(P_{NO_2})^2}{(P_{NO})^2(P_{O_2})} \)
- B) \( K_p = \frac{(P_{NO})^2(P_{O_2})}{(P_{NO_2})^2} \)
- C) \( K_p = (P_{NO_2})^2 \)
- D) \( K_p = (P_{NO})^2(P_{O_2}) \)
42. **In an endothermic reaction, what is the effect of increasing temperature on the equilibrium constant?**
- A) It increases.
- B) It decreases.
- C) It remains constant.
- D) It can be either increase or decrease depending on other factors.
43. **For the equilibrium reaction \( A(g) + B(g) ⇌ C(g) + D(g) \), which of the following is true when the volume is decreased?**
- A) The equilibrium shifts to the side with more moles of gas.
- B) The equilibrium shifts to the side with fewer moles of gas.
- C) There is no shift in equilibrium.
- D) The reaction proceeds only in the forward direction.
44. **What can be inferred from the statement "K for the reverse reaction is equal to 1/K for the forward reaction"?**
- A) The forward and reverse reactions have the same rate.
- B) The equilibrium constants for forward and reverse reactions are related.
- C) The concentrations of products and reactants are equal.
- D) The reaction has reached completion.
45. **Which of the following factors affects the equilibrium constant of a reaction?**
- A) Concentration of reactants.
- B) Temperature.
- C) Presence of a catalyst.
- D) Nature of reactants and products.
46. **The equilibrium constant \( K_c \) for the reaction \( 2H_2(g) + O_2(g) ⇌ 2H_2O(g) \) at a certain temperature is 10. What does this suggest?**
- A) The products are present in larger amounts than the reactants.
- B) The reactants are present in larger amounts than the products.
- C) The reaction does not favor either side.
- D) The reaction is at equilibrium.
47. **How would the addition of more reactants affect the equilibrium position in a reversible reaction?**
- A) The equilibrium shifts to the right.
- B) The equilibrium shifts to the left.
- C) It has no effect on the equilibrium position.
- D) The reaction will stop.
48. **If a reaction has a very small \( K \) value, what does that indicate?**
- A) The reaction favors the products.
- B) The reaction favors the reactants.
- C) The reaction goes to completion.
- D) The reaction is very fast.
49. **What happens to the equilibrium position if an exothermic reaction is subjected to an increase in temperature?**
- A) It shifts to the left.
- B) It shifts to the right.
- C) It remains unchanged.
- D) It shifts to the reactants only.
50. **In the context of the law of mass action, which of the following statements is correct?**
- A) The concentrations of products and reactants must be equal.
- B) The reaction rate is dependent on the concentration of the reactants only.
- C) The concentrations of the products at equilibrium are constant.
- D) The equilibrium constant is only applicable to gaseous reactions.
51. **If the concentration of products is greater than that of reactants in a reaction at equilibrium, what can be said about \( K \)?**
- A) \( K < 1 \)
- B) \( K = 1 \)
- C) \( K > 1 \)
- D) \( K = 0 \)
52. **In which scenario would the equilibrium constant remain unchanged?**
- A) If the temperature changes.
- B) If the concentration of a product is increased.
- C) If a catalyst is added.
- D) If the volume of the reaction vessel is altered.
53. **If the reaction \( 2C ⇌ A + B \) has an equilibrium constant of 0.5, what can be inferred?**
- A) The products are favored.
- B) The reactants are favored.
- C) The reaction goes to completion.
- D) There is equal concentration of products and reactants.
54. **Which of the following describes the effect of a catalyst on the equilibrium constant?**
- A) It increases the value of \( K \).
- B) It decreases the value of \( K \).
- C) It does not change the value of \( K \).
- D)
It changes \( K \) only in one direction.
55. **For a reaction at equilibrium, what can be inferred about the Gibbs free energy (\( \Delta G \))?**
- A) \( \Delta G < 0 \)
- B) \( \Delta G = 0 \)
- C) \( \Delta G > 0 \)
- D) \( \Delta G \) cannot be determined.
56. **In a closed system at equilibrium, what can be said about the concentrations of reactants and products over time?**
- A) They continuously change.
- B) They eventually become constant.
- C) The reactants are consumed completely.
- D) The products are consumed completely.
57. **In the expression for equilibrium constant, which of the following states of matter is not included?**
- A) Gases.
- B) Solids.
- C) Liquids.
- D) Aqueous solutions.
58. **Which of the following represents a situation where dynamic equilibrium is present?**
- A) A candle burning completely.
- B) Ice melting in a warm room.
- C) A saturated solution where dissolution and precipitation occur simultaneously.
- D) A rusting iron nail.
59. **If a reversible reaction is at equilibrium and the system is disturbed, what is the most likely outcome?**
- A) The reaction stops entirely.
- B) The reaction shifts to restore equilibrium.
- C) The products will be favored.
- D) The reactants will be favored.
60. **When a reaction is at dynamic equilibrium, which of the following statements is true?**
- A) The concentrations of reactants and products are always equal.
- B) The reaction can only proceed in one direction.
- C) The rates of the forward and reverse reactions are equal.
- D) The reaction has gone to completion.
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### Answer Key
1. B
2. C
3. C
4. A
5. B
6. D
7. C
8. B
9. A
10. A
11. B
12. C
13. A
14. C
15. A
16. A
17. A
18. B
19. B
20. A
21. A
22. B
23. C
24. B
25. C
26. B
27. A
28. C
29. B
30. B
31. B
32. A
33. C
34. A
35. C
36. C
37. A
38. A
39. B
40. A
41. A
42. A
43. B
44. B
45. B
46. A
47. A
48. B
49. A
50. C
51. C
52. C
53. B
54. C
55. B
56. B
57. B
58. C
59. B
60. C