Chemical kinetics

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

1. Which are correct units for the rate of a reaction?

A. mol dm^-3

B. mol dm^-3 s^-1

C. mol s^-1

D. mol dm^-3 s

2. 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

3. Which is a correct statement about the rate of a chemical reaction?

A. It can only be determined experimentally.

B. It can be deduced from the chemical equation for the reaction.

C. It can be predicted from the sign and value of the enthalpy change, ∆H, for the reaction.

D. It only depends on the nature of the reactants not on their concentration.

4. 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

5. A student wished to follow the rate of the reaction between calcium carbonate and
hydrochloric acid. Which of the following methods would not work?

A. Measuring the volume of carbon dioxide gas evolved over time.

B. Measuring the change in mass of the contents of the flask over time.

C. Measuring the change in colour of the contents of the flask over time.

D. Measuring the change in pH of the contents of the flask over time.

6. 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.

7. Which of the following are the advantages of using a pH probe connected to a data logger to read
the pH of a reaction over time rather than mIB Docs (2) Teamally using a pH meter to take the readings?

I. The readings can be taken at precise regular intervals.

II. Regular readings can be taken at very short time intervals.

III. Regular readings can be taken at very long time intervals.

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

8. The table shows the concentrations of reactants and products during the reaction

2X + Y → 2Z

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

9. Equal masses of excess magnesium metal were added to separate solutions of hydrochloric acid.
The volume of hydrogen evolved was measured at regular time intervals and the results presented
graphically. Which curve best represents the results obtained for the different solutions of
hydrochloric acid shown below?

10. 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.

11. 100 cm³ of 1.0 mol dm^-3 sulfuric acid is added to an excess of sodium carbonate
at 298 K. Assuming the sample of sodium carbonate is kept constant and remains in
excess which will not increase the initial rate of the reaction?

12. 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

13. Which explains why increasing the temperature increases the rate of a chemical reaction?

A. More reactant particles possess energy greater than or equal to the activation energy.

B. The activation energy decreases at higher temperatures.

C. Reactant particles travel faster at higher temperatures.

D. Reactant particles are more likely to be in the gaseous state at higher temperatures.

14. 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.

15. What is the function of solid vanadium pentoxide in the Contact process?

A. It moves the position of equilibrium in favour of more products.

B. It increases the initial rate of reaction.

C. It lowers the enthalpy change for the reaction.

D. It increases the yield of products formed.

16. 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.

17. Which is a correct statement concerning the catalysed and uncatalysed pathways for a
particular reaction?

A. The enthalpy change of the catalysed reaction is equal to the enthalpy change of the
uncatalysed reaction.

B. The enthalpy change of the catalysed reaction is lower than the enthalpy change of the
uncatalysed reaction.

C. The enthalpy change of the uncatalysed reaction is lower than the enthalpy change of
the catalysed reaction.

D. The activation energy of the uncatalysed reaction is lower than the activation energy of
the catalysed reaction.

18. Which is a true statement about two Maxwell-Boltzman 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.

19. Catalysts provide an alternative pathway for a chemical reaction. What is true about
this alternative pathway?

A. It provides a lower enthalpy change for the reaction.

B. It provides a higher activation energy for the reaction.

C. It lowers the temperature of the reaction.

D. It enables the position of equilibrium to be reached faster.

20. 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.

Answers

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