PU CET Lahore (Engineering & CS) Chemistry Chemical Equilibrium — Set 2

Chemical Equilibrium MCQs set 2 for PU CET Lahore (Engineering & CS) Chemistry — 20 solved questions.

PU CET Lahore (Engineering & CS) Chemistry Chemical Equilibrium — Set 2

  1. Question 1

    Q1. For the reaction N2 + 3H2 ⇌ 2NH3, if the initial concentrations are 1 M each, what is the equilibrium constant expression?

    • A) Kc = [NH3]² / [N2] [H2]³
    • B) Kc = [N2] [H2]³ / [NH3]²
    • C) Kc = [NH3] / [N2] [H2]
    • D) Kc = [N2] [H2] / [NH3]

    Answer: Kc = [NH3]² / [N2] [H2]³

    Explanation: The law of mass action states that Kc = [products] / [reactants] with stoichiometric coefficients as powers.

  2. Question 2

    Q2. If Kc = 64 for the reaction A + B ⇌ C + D and initial concentrations of A and B are 1 M each, what is the equilibrium concentration of C?

    • A) 0.8 M
    • B) 0.5 M
    • C) 0.2 M
    • D) 0.1 M

    Answer: 0.8 M

    Explanation: Using the Kc expression and assuming x M of A and B react, we get 64 = x² / (1-x)², solving gives x = 0.8.

  3. Question 3

    Q3. For the reaction 2NO2 ⇌ N2O4, if the degree of dissociation is α, what is the total number of moles at equilibrium?

    • A) 1 + α
    • B) 1 - α
    • C) 1 + α/2
    • D) 1 - α/2

    Answer: 1 - α/2

    Explanation: Initially 1 mole of N2O4, at equilibrium (1-α) moles of N2O4 and 2α moles of NO2, total = 1 - α + 2α = 1 + α, but for 2NO2 ⇌ N2O4, it is 1 - α/2.

  4. Question 4

    Q4. The equilibrium constant Kp for the reaction N2 + O2 ⇌ 2NO is given by

    • A) Kp = P(NO)² / P(N2) P(O2)
    • B) Kp = P(N2) P(O2) / P(NO)²
    • C) Kp = P(NO) / P(N2) P(O2)
    • D) Kp = P(N2) / P(NO)²

    Answer: Kp = P(NO)² / P(N2) P(O2)

    Explanation: Kp is defined as the ratio of partial pressures of products to reactants, with stoichiometric coefficients as powers.

  5. Question 5

    Q5. For the reaction CO + H2O ⇌ CO2 + H2, if Kc = 4 and initial concentrations of CO and H2O are 1 M each, what is [CO] at equilibrium?

    • A) 0.33 M
    • B) 0.5 M
    • C) 0.67 M
    • D) 0.25 M

    Answer: 0.33 M

    Explanation: Using Kc = [CO2][H2]/[CO][H2O] and assuming x M react, we get 4 = x²/(1-x)², solving gives x = 2/3.

  6. Question 6

    Q6. The value of Kc for the reaction A ⇌ 2B is 4. If the initial concentration of A is 1 M, what is [B] at equilibrium?

    • A) 0.8 M
    • B) 1 M
    • C) 0.5 M
    • D) 0.2 M

    Answer: 0.8 M

    Explanation: Kc = [B]²/[A], assuming x M of A reacts, 4 = (2x)²/(1-x), solving gives x = 0.4, hence [B] = 2x = 0.8.

  7. Question 7

    Q7. For a reaction, if Kc > 1, what does it indicate?

    • A) Reaction is spontaneous
    • B) Reaction is at equilibrium
    • C) Products are favored
    • D) Reactants are favored

    Answer: Products are favored

    Explanation: Kc > 1 indicates that the concentration of products is more than reactants at equilibrium.

  8. Question 8

    Q8. For the reaction 2SO2 + O2 ⇌ 2SO3, if Kc = 100 and initial concentrations of SO2 and O2 are 2 M and 1 M, what is [SO3] at equilibrium?

    • A) 1.8 M
    • B) 1.5 M
    • C) 1 M
    • D) 0.5 M

    Answer: 1.8 M

    Explanation: Using Kc = [SO3]²/[SO2]²[O2] and assuming x M of SO2 reacts, we get 100 = x²/(2-x)²(1-x/2), solving gives x = 1.8/2 = 0.9, [SO3] = 1.8.

  9. Question 9

    Q9. For a reaction, if Δn = 0, what is the relation between Kp and Kc?

    • A) Kp = Kc
    • B) Kp = Kc(RT)
    • C) Kp = Kc/(RT)
    • D) Kp = Kc(RT)²

    Answer: Kp = Kc

    Explanation: Kp = Kc(RT)^Δn, when Δn = 0, Kp = Kc.

  10. Question 10

    Q10. The equilibrium constant Kc for the reaction H2 + I2 ⇌ 2HI is 50. If the initial concentrations of H2 and I2 are 1 M each, what is [HI] at equilibrium?

    • A) 1.56 M
    • B) 1 M
    • C) 0.5 M
    • D) 1.8 M

    Answer: 1.56 M

    Explanation: Using Kc = [HI]²/[H2][I2] and assuming x M react, 50 = (2x)²/(1-x)², solving gives x = 0.78, [HI] = 1.56.

  11. Question 11

    Q11. For the reaction N2O4 ⇌ 2NO2, if the degree of dissociation is α, what is the equilibrium constant Kp?

    • A) Kp = 4α²/(1-α²)P
    • B) Kp = 4α²/(1-α)P
    • C) Kp = α²/(1-α)P
    • D) Kp = 4α/(1-α)P

    Answer: Kp = 4α²/(1-α²)P

    Explanation: Kp = (P(NO2))²/P(N2O4), using partial pressures in terms of α and P, we get Kp = 4α²P/(1-α²).

  12. Question 12

    Q12. For a reaction, if the temperature is increased, what happens to Kc?

    • A) Increases for exothermic reactions
    • B) Decreases for endothermic reactions
    • C) Remains the same
    • D) Increases for endothermic reactions

    Answer: Increases for endothermic reactions

    Explanation: For endothermic reactions, increasing temperature favors products, hence Kc increases.

  13. Question 13

    Q13. The value of Kc for the reaction 2A ⇌ B + C is 0.5. If the initial concentration of A is 2 M, what is [B] at equilibrium?

    • A) 0.5 M
    • B) 1 M
    • C) 0.25 M
    • D) 0.75 M

    Answer: 0.25 M

    Explanation: Kc = [B][C]/[A]², assuming x M of A reacts, 0.5 = x²/(2-2x)², solving gives x = 0.5, [B] = 0.25.

  14. Question 14

    Q14. For the reaction CO2 + H2 ⇌ CO + H2O, if Kc = 0.1 and initial concentrations of CO2 and H2 are 1 M each, what is [CO] at equilibrium?

    • A) 0.27 M
    • B) 0.3 M
    • C) 0.25 M
    • D) 0.2 M

    Answer: 0.27 M

    Explanation: Using Kc = [CO][H2O]/[CO2][H2] and assuming x M react, 0.1 = x²/(1-x)², solving gives x = 0.27.

  15. Question 15

    Q15. For a reaction, if the volume is decreased, what happens to the equilibrium?

    • A) Shifts towards the side with more moles
    • B) Shifts towards the side with less moles
    • C) Remains the same
    • D) Cannot be predicted

    Answer: Shifts towards the side with less moles

    Explanation: Decreasing volume increases pressure, hence equilibrium shifts to the side with less moles to counteract the change.

  16. Question 16

    Q16. The equilibrium constant Kc for the reaction A + B ⇌ C is 4. If the initial concentrations of A and B are 1 M each, what is [C] at equilibrium?

    • A) 0.67 M
    • B) 0.5 M
    • C) 0.8 M
    • D) 0.2 M

    Answer: 0.67 M

    Explanation: Using Kc = [C]/[A][B] and assuming x M react, 4 = x/(1-x)², solving gives x = 0.67 (approx).

  17. Question 17

    Q17. For the reaction 2NO ⇌ N2 + O2, if Kc = 0.1 and initial concentration of NO is 2 M, what is [N2] at equilibrium?

    • A) 0.33 M
    • B) 0.25 M
    • C) 0.5 M
    • D) 0.1 M

    Answer: 0.25 M

    Explanation: Kc = [N2][O2]/[NO]², assuming x M of NO reacts, 0.1 = x²/(2-2x)², solving gives x = 0.25 (approx).

  18. Question 18

    Q18. For a reaction, if a catalyst is added, what happens to the equilibrium constant?

    • A) Increases
    • B) Decreases
    • C) Remains the same
    • D) Cannot be predicted

    Answer: Remains the same

    Explanation: A catalyst speeds up both forward and backward reactions equally, hence equilibrium constant remains unchanged.

  19. Question 19

    Q19. For the reaction N2 + 3H2 ⇌ 2NH3, what is the effect of increasing pressure on equilibrium?

    • A) Shifts to the right
    • B) Shifts to the left
    • C) No effect
    • D) Cannot be predicted

    Answer: Shifts to the right

    Explanation: Increasing pressure favors the side with fewer moles of gas, according to Le Chatelier's principle, so it shifts to the right.

  20. Question 20

    Q20. What is the expression for Kc for the reaction 2NO2 ⇌ N2O4?

    • A) [N2O4] / [NO2]
    • B) [N2O4] / [NO2]²
    • C) [NO2]² / [N2O4]
    • D) [NO2] / [N2O4]

    Answer: [N2O4] / [NO2]²

    Explanation: Kc = [products] / [reactants] raised to their stoichiometric coefficients, so Kc = [N2O4] / [NO2]².

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Level 1

For the reaction N2 + 3H2 ⇌ 2NH3, if the initial concentrations are 1 M each, what is the equilibrium constant expression?