Chemical kinetics (2)

For each question choose the answer you consider to be the best.

1. Which statement best defines rate of reaction?

A. The time taken for the reaction to reach completion.

B. The speed at which the reaction occurs.

C. The change in concentration of a reactant or product over time.

D. The increase in concentration of a reactant over time

2. Which of the following could be used to follow the rate of a reaction?

I. Change in temperature as the reaction proceeds

II. Change in colour as the reaction proceeds

III. Change in electrical conductivity as the reaction proceeds

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

3. Which would be the best method to measure the rate of the reaction between an unsaturated fat and iodine?

A. Measuring the change in mass of the contents of the reaction vessel over time.

B. Measuring the change in colour of the contents of the reaction vessel over time.

C. Measuring the volume of gas evolved over time.

D. Measuring the change in conductivity over time.

4. The table shows the concentrations of reactants and products during the reaction of X and Y to produce Z.
 

The rate of a reaction can be referenced to any reactant or product. Which is a correct statement about the rate of the reaction?

A. Rate = 0.2 mol dm^-3 s^-1 with reference to X

B. Rate = 1.0 mol dm^-3 s^-1 with reference to Y

C. Rate = – 0.2 mol dm^-3 s^-1 with reference to Y

D. Rate = 0.2 mol dm^-3 s^-1 with reference to Z

5. For two particles to react when they collide what must be true according to collision theory?

A. They must both have the same kinetic energy.

B. All their chemical bonds must be broken.

C. They must collide with the correct geometry or orientation.

D. They must be in the gaseous or liquid state.

6. Which of the following factors affect the rate of a reaction according to collision theory?

I. The frequency of the collisions between reactant particles.

II. The orientation of the particles when they collide.

III. The number of reactant particles with E greater than or equal to E_a.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

7. Which will not generally increase the rate of a chemical reaction?

A. Increasing the surface area of solid reactant particles.

B. Increasing the size of solid reactant particles.

C. Increasing the concentration of the reactant particles.

D. Decreasing the activation energy.

8. Iron reacts with sulfuric acid according to the equation

Fe(s) + H₂SO₄(aq) → FeSO₄(aq) + H₂(g)

Exactly 1.0 g of iron powder from the same bottle was added to separate samples of excess sulfuric acid in two separate experiments.

Experiment 1. Iron added to 100 cm³ of 1.0 mol dm^-3 H₂SO₄(aq)
Experiment 2. Iron added to 200 cm³ of 2.0 mol dm^-3 H₂SO₄(aq)

Which will be the same for both reactions?

A. The volume of hydrogen gas evolved.

B. The initial rate of reaction.

C. The increase in temperature of the solution.

D. The total time taken for the reaction to finish.

9. Which is a true statement about two Maxwell-Boltman energy distribution curves drawn for a fixed amount of gas at two different temperatures, T K and (T+10) K?

A. Both curves will peak at the same height.

B. The area under both curves will be the same.

C. Both curves will have the same number of particles with higher energy.

D. The average energy for both curves will be the same.

10. A reaction between an acid and a metal carbonate takes 60 seconds before it is completed. Why is the initial rate of the reaction faster than the rate after 50 seconds?

A. The concentration of the acid decreases during the reaction.

B. The temperature of the reaction decreases as it proceeds.

C. The particle size of the metal carbonate decreases as the reaction proceeds.

D. The carbon dioxide produced dissolves in the water as the reaction proceeds.

11. Which is a correct statement about the overall order of a reaction?

A. It can be deduced from the balanced equation for the reaction.

B. It changes when the concentration of the reactants change.

C. It can only be determined by experiment.

D. It is equal to the product of all the powers that the concentration of each reactant is raised to in the rate equation.

12. The following mechanism has been proposed for the reaction between nitrogen(II) oxide and oxygen to give nitrogen(IV) oxide.
2NO(g) →N₂O₂(g) fast
N₂O₂(g) + O₂(g) → 2NO₂(g) slow

What is a possible rate equation for this reaction?

A. rate = k[NO(g)]²

B. rate = k[N₂O₂(g)][O₂(g)]

C. rate = k[NO(g)]²[O₂(g)]

D. rate = k[NO(g)][O₂(g)]

13. Which is the best description of the rate determining step for a reaction?

A. The fastest step in the reaction pathway.

B. The step with the fewest number of reactant molecules.

C. The step with the lowest enthalpy change.

D. The step with the highest activation energy.

14. The rate expression for a reaction is rate = k [A][B]²

Which statement is correct?

A. As the concentration of A increases the concentration of B decreases.

B. As the temperature increases the rate constant decreases.

C. The rate constant is not affected by temperature.

D. If the concentrations of A and B are doubled the rate increases eight times.

15. Consider the following mechanism for a nucleophilic substitution reaction.

Step 1: C(CH₃)₃Br → C(CH₃)₃⁺ + Br⁻ slow

Step 2: C(CH₃)₃⁺ + OH^– → C(CH₃)₃OH fast

Which statement correctly identifies the rate-determining step with the correct explanation?

A. Step 1 because it is the slower step.

B. Step 2 because it is the faster step.

C. Step 1 because it is the first step.

D. Step 2 because it is the second step.

16. The reaction between propanone and iodine in acid solution was followed by measuring the time taken for yellow colour of the iodine present in the mixture to disappear as the concentrations of the reactants were altered. The following results were obtained.

What is the correct order of the reaction with respect to each of the three reactants?

17. The rate constant for a reaction has the units s^-1. What is the order of the reaction?

A. 0

B. 1

C. 2

D. 3

18. The rate expression for the reaction between hydrogen gas and iodine gas to produce hydrogen iodide gas is

rate = k[H₂(g)][I₂(g)]

Which is a correct statement about the rate expression for the reaction between hydrogen gas and bromine gas?

H₂(g) + Br₂(g) → 2HBr(g)

A. rate = k[H₂(g)][Br₂(g)]

B. rate = k[HBr(g)]²

C. rate = k[2HBr(g)]²

D. It is impossible to give the expression based on the information given.

19. Which of the following statements are correct?

I. The rate constant of a reaction increases with temperature.

II. The Arrhenius constant A, in the Arrhenius expression lnk = lnA – E_a/RT is related to the geometry of the collisions.

III. The activation energy of a reaction increases with temperature.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

20. The change in the value of the rate constant (k), for a reaction as the temperature (T) was increased was determined experimentally. A graph of lnk against 1/T was then plotted to determine the activation energy (E_a) and the Arrhenius constant (A) for the reaction.

Which is a true statement?

A. The gradient = – E_a/R and the intercept on the lnk axis = lnA.

B. The gradient = – E_a/RT and the intercept on the lnk axis = lnA.

C. The gradient = E_a/R and the intercept on the lnk axis = – lnA.

D. The gradient = E_a/RT and the intercept on the lnk axis = – lnA.

Answers

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