Lesson 5.1.1

5.1.1 How fast Quiz: OCR Chemistry, Unit 4

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 5.1.1, How fast: 20 multiple choice questions for the OCR Chemistry (H432), Unit 4: Physical chemistry and transition elements, written with Revision Ninja.

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The 20 questions

  1. What is the overall order of a reaction whose rate equation is rate = k[A][B]^2?

    • 3
    • 2
    • 5
    • 1

  2. What term describes the slowest step in a multi-step reaction mechanism?

    • Rate-determining step
    • Activation step
    • Propagation step
    • Overall reaction order

  3. What are the units of the rate constant k for a reaction with rate = k[A]^2?

    • mol dm^-3 s^-1
    • s^-1
    • dm^6 mol^-2 s^-2
    • dm^3 mol^-1 s^-1

  4. What term is the time taken for a reactant's concentration to decrease by half?

    • Induction period
    • Half-life
    • Reaction order
    • Rate constant

  5. How does the half-life of a first-order reaction change as reactant concentration decreases?

    • Decreases by half
    • Increases continuously
    • Doubles each time
    • Remains constant

  6. What is the shape of a concentration-time graph for a zero-order reactant?

    • Upward sloping curve
    • Downward straight line
    • Exponential decay curve
    • Horizontal straight line

  7. A rate-concentration graph for a reactant is a horizontal straight line. What is the order with respect to that reactant?

    • Zero order
    • First order
    • Second order
    • Third order

  8. A first order reaction has a half-life of 50 s. What is the rate constant k, to two significant figures?

    • 0.035 s^-1
    • 0.014 s^-1
    • 1.4 s^-1
    • 0.0069 s^-1

  9. Reactant concentration falls from 1.00 mol dm^-3 to 0.50 mol dm^-3 in 40 s in a first order reaction. How long does it take to fall from 0.50 to 0.25 mol dm^-3?

    • 20 s
    • 40 s
    • 80 s
    • 10 s

  10. Reactant concentration falls from 0.80 to 0.40 mol dm^-3 in a reaction. Over the 200 s interval the average rate is measured as the change over time. What is this average rate?

    • 0.0040 mol dm^-3 s^-1
    • 0.20 mol dm^-3 s^-1
    • 0.00050 mol dm^-3 s^-1
    • 0.0020 mol dm^-3 s^-1

  11. Initial rate experiments show that doubling [A] doubles the rate and doubling [B] increases the rate four times. What is the rate equation?

    • rate = k[A]^2[B]^2
    • rate = k[A]^2[B]
    • rate = k[A][B]
    • rate = k[A][B]^2

  12. For a reaction with rate = k[A][B]^2, the rate is 0.0032 mol dm^-3 s^-1 when [A] = 0.20 mol dm^-3 and [B] = 0.10 mol dm^-3. What is k?

    • 0.625 mol^-2 dm^6 s^-1
    • 1.6 mol^-2 dm^6 s^-1
    • 1.6 s^-1
    • 16 mol^-2 dm^6 s^-1

  13. A first order reaction has rate constant k = 0.0462 s^-1. What is its half-life?

    • 32.1 s
    • 0.0327 s
    • 15.0 s
    • 7.5 s

  14. In a clock reaction, what quantity is inversely proportional to the time measured?

    • Activation energy
    • Initial rate
    • Rate constant
    • Order of reaction

  15. For rate = k[A][B], how many molecules of A feature in the rate-determining step?

    • Two molecules
    • Three molecules
    • One molecule
    • Zero molecules

  16. A plot of ln k against 1/T for a reaction has a gradient of -4000 K. Using R = 8.31 J K^-1 mol^-1, what is the activation energy?

    • 0.48 kJ mol^-1
    • 33.2 kJ mol^-1
    • 4000 kJ mol^-1
    • 481 kJ mol^-1

  17. A plot of ln k against 1/T has a gradient of -9.0 x 10^3 K. What is the activation energy, using R = 8.31 J K^-1 mol^-1?

    • 74.8 kJ mol^-1
    • 9.0 kJ mol^-1
    • 748 kJ mol^-1
    • 1.08 kJ mol^-1

  18. What increases when temperature rises, causing the rate constant to increase?

    • Frequency of collisions
    • Overall enthalpy change
    • Total activation energy
    • Proportion exceeding Ea

  19. Which equation is the Arrhenius equation?

    • k = A e^(Ea/RT)
    • k = ln 2 / t1/2
    • k = A e^(-Ea/RT)
    • rate = k[A]^m[B]^n

  20. What is the shape of a rate-concentration graph for a second-order reactant?

    • Upward curve
    • Downward curve
    • Horizontal line
    • Sloping straight line

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