1. The potential energy diagram below refers to the reversible reaction involving reactants R and products P.
What is the enthalpy change, in kJ mol–1, for the reverse reaction P → R?
A + 30
B + 10
C –10
D –40
2. The following potential diagram is for a reaction carried out with and without a catalyst.
The activation energy for the catalysed reaction is
A 30 kJ mol–1
B 80 kJ mol–1
C 100 kJ mol–1
D 130 kJ mol–1.
3. A potential energy diagram can be used to show the activation energy (EA) and the enthalpy change (ΔH) for a reaction. Which of the following combinations of EA and ΔH could never be obtained for a reaction?
A EA = 50 kJ mol–1 and ΔH = –100 kJ mol–1
B EA = 50 kJ mol–1 and ΔH = +100 kJ mol–1
C EA = 100 kJ mol–1 and ΔH = +50 kJ mol–1
D EA = 100 kJ mol–1 and ΔH = –50 kJ mol–1
4. For any chemical, its temperature is a measure of
A the average kinetic energy of the particles that react
B the average kinetic energy of all the particles
C the activation energy
D the minimum kinetic energy required before reaction occurs.
5. When a catalyst is used, the activation energy of the forward reaction is reduced to 35 kJ mol–1.
What is the activation energy of the catalysed reverse reaction?
A 30 kJ mol–1
B 35 kJ mol–1
C 65 kJ mol–1
D 190 kJ mol–1
6. A reaction was carried out with and without a catalyst as shown in the energy diagram.
What is the enthalpy change, in kJ mol–1 for the catalysed reaction?
A –100
B –50
C +50
D +100
7. Which of the following is not a correct statement about the effect of a catalyst?
The catalyst
A provides an alternative route to the products
B lowers the energy that molecules need for successful collisions
C provides energy so that more molecules have successful collisions
D forms bonds with reacting molecules.
8. a) Copy the diagrams below and mark with an arrow:-
i) the activation energy EA.
ii) the enthalpy change H
b) State whether each reaction is endothermic or exothermic.
c) Calculate the value of H and EA for each reaction
9. Copy the axes below and sketch potential energy diagrams for the following reactions, labelling the axes.
a) H = -15 kJ mol-1 EA = 20 kJ mol-1
b) H = +20 kJ mol-1 EA = 35 kJ mol-1
10. Two chemicals A and B react in solution to form C. The reaction has an activation energy of 150 kJ mol-1. If hydrogen ions are used as a catalyst the activation energy is 50 kJ mol-1. The enthalpy change for the reaction is -125 kJ mol-1. Present this information as a potential energy diagram using the template below.
Use a solid line for the uncatalysed reaction and a dotted line for the catalysed reaction.
11. The graph shows the potential energy diagram for a urease catalysis of urea.
(a) What is the enthalpy change for the reaction?
(b) Acid is a less effective catalyst than urease for this reaction.
Sketch the diagram and add a curve to the potential energy diagram to show the hydrolysis when acid is used as the catalyst.
12. (a) Graph 1 shows the distribution of kinetic energies of molecules in a gas at300C
Copy the graph and add a dotted line to show the distribution of kinetic energies at 200C.
(b) In Graph 2, the shaded area represents the number of molecules with the required energy of activation, EA, for reaction to occur.
Copy the graph and draw a line to show how a catalyst affects the energy of activation.
(c) A collision involving molecules with the required energy of activation may not result in reaction.
State a reason for this.
13. What is meant by the term “activation energy”?
14. The decomposition of an aqueous solution of hydrogen peroxide into oxygen and water can be catalysed by iodide ions, I-(aq), or by solid manganese (IV) oxide, MnO2(s).
For each of these catalysts state, with a reason, whether the catalysis is homogeneous or heterogeneous.
An advice leaflet given to motorists when catalytic converters were first used states: “Cars fitted with catalytic converters must be run on unleaded petrol only.”
(a) Outline the reasons for fitting catalytic converters, naming the substances reacting and what happens to them.
(b) Describe in terms of adsorption how catalysts work, and state the effect this has on the activation energy for the reaction.
(c) Describe how a substance poisons a catalyst.
(d) Explain the reason for the advice given at the start of the question.
15.
16. In area X
A molecules always form an activated complex
B no molecules have the energy to form an activated complex
C collisions between molecules are always successful in forming products
D all molecules have the energy to form an activated complex.
17. The reaction of oxalic acid with an acidified solution of potassium permanganate was studied to determine the effect of temperature changes on reaction rate.
The reaction was carried out at several temperatures between 40 °C and 60 °C. The end of the reaction was indicated by a colour change from purple to colourless.
(a) (i) State two factors that should be kept the same in these experiments.
(ii) Why is it difficult to measure an accurate value for the reaction time when the reaction is carried out at room temperature?
(b) Sketch a graph to show how the rate varied with increasing temperature.
18. As a rough guide, the rate of a reaction tends to double for every 10 °C rise in temperature.
Why does a small increase in temperature produce a large increase in reaction rate?
19. Enzymes are biological catalysts. They catalyse the chemical reactions which take place in the living cells of plants and animals. For example, the enzyme invertase catalyses the reaction of sucrose and water to give glucose and fructose. Enzymes are used in the manufacture of cheese, yoghurt, bread, wine, beer, lager, whisky and biological detergents. There are, therefore, many everyday examples of enzymes and they are used in many industrial processes.
a) Explain the meaning of the word catalyst.
b) Distinguish between the terms homogeneous and heterogeneous catalyst.
c) Rhodium, platinum and palladium are present as catalysts in the catalytic converters found in motor car exhaust systems. To what type of catalysts do they belong?
Explain your answer.
d) The enzyme catalase dissolves in water and the solution catalyses the decomposition of a solution of hydrogen peroxide in water. What type of catalysis is taking place?
20. Use the collision theory to explain why
a) increasing the concentration of a reactant increases reaction rate.
b) decreasing the particle size of a solid reactant increases reaction rate.
c) increasing the temperature increases the rate of reactions.
21. Many transition metals can act as catalysts. Which of the following is a
transition metal?
A Barium
B Gallium
C Vanadium
D Antimony
22. Kurt intended to study the effect of change in acid concentration on the reaction between nitric acid and limestone to produce carbon dioxide gas. He decided to monitor the mass of the flask as the reaction proceeded. Which of the following need not be kept constant?
A the temperature of the acid
B the shape of the flask
C the particle size of the limestone
D the mass of the limestone
