PIEAS Entry Test Chemistry Reaction Kinetics — Set 2

Reaction Kinetics MCQs set 2 for PIEAS Entry Test Chemistry — 20 solved questions.

PIEAS Entry Test Chemistry Reaction Kinetics — Set 2

  1. Question 1

    Q1. For a first-order reaction, the rate constant is 0.02 s-1. What is the half-life?

    • A) 34.65 s
    • B) 43.32 s
    • C) 20 s
    • D) 50 s

    Answer: 34.65 s

    Explanation: For a first-order reaction, t1/2 = ln(2) / k = 0.693 / 0.02 = 34.65 s, using the formula t1/2 = ln(2) / k.

  2. Question 2

    Q2. The rate law for the reaction 2A + B -> C is rate = k[A]²[B]. If [A] is doubled and [B] is halved, the rate will be

    • A) double
    • B) half
    • C) unchanged
    • D) quadrupled but then halved, so doubled

    Answer: quadrupled but then halved, so doubled

    Explanation: New rate = k(2[A])²([B]/2) = k(4[A]²)([B]/2) = 2k[A]²[B], so the rate is doubled.

  3. Question 3

    Q3. For the reaction A -> B, the rate constant is 0.01 min-1. If the initial concentration of A is 1 M, what is [A] after 100 min?

    • A) 0.37 M
    • B) 0.1 M
    • C) 0.5 M
    • D) 0.25 M

    Answer: 0.37 M

    Explanation: For a first-order reaction, [A] = [A]0 * e^(-kt) = 1 * e^(-0.01*100) = e^(-1) = 0.37 M.

  4. Question 4

    Q4. The rate of a reaction is given by rate = k[A][B]. If the concentration of A is doubled, the rate will

    • A) remain the same
    • B) be doubled
    • C) be halved
    • D) be quadrupled

    Answer: be doubled

    Explanation: New rate = k(2[A])[B] = 2k[A][B], so the rate is doubled.

  5. Question 5

    Q5. For the reaction 2NO + O2 -> 2NO2, the rate law is rate = k[NO]²[O2]. The order with respect to NO is

    • A) 1
    • B) 2
    • C) 3
    • D) 0

    Answer: 2

    Explanation: The rate law is rate = k[NO]²[O2], so the order with respect to NO is 2.

  6. Question 6

    Q6. The half-life of a first-order reaction is 20 min. What is the rate constant?

    • A) 0.0347 min-1
    • B) 0.05 min-1
    • C) 0.02 min-1
    • D) 0.01 min-1

    Answer: 0.0347 min-1

    Explanation: For a first-order reaction, t1/2 = 0.693 / k, so k = 0.693 / 20 = 0.0347 min-1.

  7. Question 7

    Q7. The rate constant for a reaction is 0.05 s-1 at 300 K. If the activation energy is 100 kJ/mol, what is the rate constant at 320 K?

    • A) 0.15 s-1
    • B) 0.2 s-1
    • C) 0.1 s-1
    • D) 0.25 s-1

    Answer: 0.15 s-1

    Explanation: Using the Arrhenius equation, we can calculate k2 = 0.15 s-1.

  8. Question 8

    Q8. The rate law for a reaction is rate = k[A]. The unit of k is

    • A) s-1
    • B) M/s
    • C) M-1s-1
    • D) M-2s-1

    Answer: s-1

    Explanation: For a first-order reaction, the unit of k is s-1.

  9. Question 9

    Q9. For the reaction A + B -> C, the rate law is rate = k[A][B]. If [A] = [B] = 1 M, the rate is 0.01 M/s. What is k?

    • A) 0.01 M-1s-1
    • B) 0.1 M-1s-1
    • C) 1 M-1s-1
    • D) 0.001 M-1s-1

    Answer: 0.01 M-1s-1

    Explanation: k = rate / ([A][B]) = 0.01 / (1*1) = 0.01 M-1s-1.

  10. Question 10

    Q10. For a second-order reaction, the rate constant is 0.01 M-1s-1. If the initial concentration is 1 M, what is the half-life?

    • A) 100 s
    • B) 50 s
    • C) 200 s
    • D) 150 s

    Answer: 100 s

    Explanation: For a second-order reaction, t1/2 = 1 / (k[A]0) = 1 / (0.01*1) = 100 s.

  11. Question 11

    Q11. The rate of a reaction is given by rate = k[A]². If [A] is doubled, the rate will be

    • A) 4 times
    • B) 2 times
    • C) 8 times
    • D) unchanged

    Answer: 4 times

    Explanation: New rate = k(2[A])² = 4k[A]², so the rate is 4 times the original rate.

  12. Question 12

    Q12. For a first-order reaction, the rate constant is 0.05 min-1. What is the time required for 75% completion?

    • A) 27.72 min
    • B) 20 min
    • C) 30 min
    • D) 40 min

    Answer: 27.72 min

    Explanation: For a first-order reaction, t = (ln([A]0/[A])) / k = (ln(100/25)) / 0.05 = 27.72 min.

  13. Question 13

    Q13. The rate constant for a reaction is 0.02 s-1. If the initial concentration is 1 M, what is [A] after 50 s?

    • A) 0.37 M
    • B) 0.25 M
    • C) 0.1 M
    • D) 0.05 M

    Answer: 0.37 M

    Explanation: For a first-order reaction, [A] = [A]0 * e^(-kt) = 1 * e^(-0.02*50) = e^(-1) = 0.37 M.

  14. Question 14

    Q14. For the reaction 2A -> B, the rate law is rate = k[A]². The order with respect to A is

    • A) 1
    • B) 2
    • C) 3
    • D) 0

    Answer: 2

    Explanation: The rate law is rate = k[A]², so the order with respect to A is 2.

  15. Question 15

    Q15. The half-life of a zero-order reaction is 20 s. If the initial concentration is 1 M, what is the rate constant?

    • A) 0.025 M/s
    • B) 0.05 M/s
    • C) 0.01 M/s
    • D) 0.1 M/s

    Answer: 0.025 M/s

    Explanation: For a zero-order reaction, t1/2 = [A]0 / (2k), so k = [A]0 / (2*t1/2) = 1 / (2*20) = 0.025 M/s.

  16. Question 16

    Q16. The rate constant for a reaction is 0.01 M-1s-1. The order of the reaction is

    • A) 1
    • B) 2
    • C) 0
    • D) 3

    Answer: 2

    Explanation: The unit of k is M-1s-1, indicating a second-order reaction.

  17. Question 17

    Q17. For a first-order reaction, the rate constant is 0.02 min-1. What is the time required for 90% completion?

    • A) 115.13 min
    • B) 100 min
    • C) 120 min
    • D) 150 min

    Answer: 115.13 min

    Explanation: For a first-order reaction, t = (ln([A]0/[A])) / k = (ln(100/10)) / 0.02 = 115.13 min.

  18. Question 18

    Q18. For a first-order reaction, the rate constant (k) is related to half-life (t1/2) as

    • A) k = 0.693 / t1/2
    • B) k = t1/2 / 0.693
    • C) k = 2.303 / t1/2
    • D) k = t1/2 / 2.303

    Answer: k = 0.693 / t1/2

    Explanation: For a first-order reaction, t1/2 = 0.693 / k. Rearranging gives k = 0.693 / t1/2, using the formula for half-life of first-order reactions.

  19. Question 19

    Q19. The rate of reaction A + B -> products is given by rate = k[A][B]. The reaction is

    • A) first-order
    • B) second-order
    • C) third-order
    • D) zero-order

    Answer: second-order

    Explanation: The overall order is the sum of the orders with respect to each reactant. Here, it's 1 + 1 = 2, making it second-order.

  20. Question 20

    Q20. The activation energy (Ea) of a reaction can be determined using the

    • A) Arrhenius equation
    • B) Michaelis-Menten equation
    • C) Henderson-Hasselbalch equation
    • D) Nernst equation

    Answer: Arrhenius equation

    Explanation: The Arrhenius equation, k = Ae^(-Ea/RT), relates the rate constant (k) to activation energy (Ea), where A is the pre-exponential factor.

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Level 1

For a first-order reaction, the rate constant is 0.02 s-1. What is the half-life?