16.1.1 Rate equations and orders of reaction Quiz: Pearson Edexcel Chemistry, Unit 16

The 20 questions

1. What is the rate of a reaction?

   • The temperature rise of the reaction mixture per second
   • The number of collisions per second regardless of their energy
   • The total mass of products formed in a year
   • The change in concentration of a reactant or product per unit time

2. What is a rate equation?

   • An equation for the equilibrium constant of a reaction, which depends on the concentrations
   • An equation showing how the rate depends on reactant concentrations, such as rate = k[A]^m[B]^n
   • A balanced equation giving only stoichiometry, from which the rate can be read directly
   • An equation giving the enthalpy change of a reaction under standard conditions at 298 K

3. What is the order of reaction with respect to a reactant?

   • The mass of the reactant used in the experiment, measured at the start of each run
   • The temperature coefficient for that reactant, which describes how its rate changes with heat
   • The power to which that reactant's concentration is raised in the rate equation
   • The number of moles of that reactant in the balanced equation, which always sets the order

4. What is the overall order of a reaction?

   • The number of reactants in the balanced equation
   • The largest coefficient in the balanced equation
   • The total number of moles of products formed
   • The sum of the individual orders in the rate equation

5. What is the rate constant, k?

   • A constant that is the same at every temperature and for every reaction in the same flask
   • The constant in the rate equation, whose value depends on temperature
   • The rate when all concentrations are zero, which is measured at the start of the experiment
   • The number of collisions per second between reactants that have enough energy to react

6. What is the half-life of a reaction?

   • The time taken for the rate to double as the temperature rises by 10 K
   • The time taken for the reaction to reach completion, which is always twice the half-life
   • The time taken for the concentration of a reactant to fall to half its initial value
   • Half the time needed for equilibrium to be reached, measured from the start of the reaction

7. What is the rate-determining step of a mechanism?

   • The fastest step in the mechanism, which therefore controls the overall rate of the reaction
   • The slowest step, which controls the overall rate of the reaction
   • The first step in every mechanism, in which the reactants first collide with each other
   • The step that produces the final product, which is always the last step of the mechanism

8. For rate = k[A]^2, what is the effect of doubling [A] on the rate?

   • The rate increases by a factor of 4
   • The rate increases by a factor of 8
   • The rate is unchanged
   • The rate doubles

9. For rate = k[A][B], what is the effect of tripling [A] and halving [B]?

   • The rate halves
   • The rate increases by a factor of 1.5
   • The rate increases by a factor of 6
   • The rate triples

10. A reaction is zero order with respect to a reactant. What happens to the rate when that reactant's concentration doubles?

    • The rate doubles
    • The rate is unchanged
    • The rate quadruples
    • The rate halves

11. Initial-rate data show that doubling [A] from 0.10 to 0.20 mol dm-3 increases the rate fourfold. What is the order with respect to A?

    • 1
    • 2
    • 3
    • 0

12. A first-order reaction has a half-life of 20 s. What fraction of the reactant remains after 60 s?

    • 6.25%
    • 12.5%
    • 33%
    • 25%

13. For rate = k[A]^2, the rate is 4.0 x 10^-4 mol dm-3 s-1 when [A] = 0.20 mol dm-3. What is k?

    • 100 dm3 mol-1 s-1
    • 0.0020 dm3 mol-1 s-1
    • 0.0016 dm3 mol-1 s-1
    • 0.0100 dm3 mol-1 s-1

14. What are the units of k for a reaction that is first order in A and first order in B?

    • mol dm-3 s-1
    • dm3 mol-1 s-1
    • mol2 dm-6 s-1
    • s-1

15. If the rate equation is rate = k[NO]^2[H2], which species are included in the rate-determining step?

    • Two NO molecules and one H2 molecule
    • One NO molecule only, because the rate depends only on the nitrogen monoxide concentration
    • One NO and one H2 molecule, which are the only reactants that appear in the rate equation
    • Two H2 molecules only, since hydrogen is the species present in greatest excess

16. What is the rate constant for a first-order reaction with a half-life of 20 s?

    • 0.0100 s-1
    • 20 s-1
    • 0.0347 s-1
    • 0.693 s-1

17. Three experiments show that doubling [A] doubles the rate, and tripling [B] increases the rate ninefold. What is the overall order?

    • 4
    • 1
    • 2
    • 3

18. A student says the order of reaction must equal the stoichiometric coefficient of each reactant. Which evaluation is best?

    • True, because the rate equation is always the balanced equation
    • False, because the order can only be found from equations with three reactants
    • False, because orders must be found experimentally and need not match the coefficients
    • True, because orders are always integers equal to the coefficients

19. Which technique could be used to track the rate of a reaction that produces a gas?

    • Measuring the mass of the solid reactants before the reaction
    • Measuring the boiling temperature of the solvent
    • Collecting the gas volume over time with a gas syringe
    • Using a melting point apparatus to measure the product

20. Why does the rate constant of a first-order reaction depend only on temperature (and any catalyst)?

    • The concentration is squared in the rate equation, so k depends on the square of the concentration
    • The half-life is always 1 s, so k has a fixed value
    • First-order reactions are independent of temperature
    • k is independent of concentration and changes with temperature and catalyst for a given mechanism

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