Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Unit
Physical Chemistry
442 practice questions
Topics covered
Practice questions
101–110 of 188 · Normal
Question 101
2 marks · Normal
Answer and see the solution →State what a reaction profile diagram shows about the effect of a catalyst on: (i) the activation energy (ii) the overall energy change (enthalpy change, ).
Question 102
4 marks · Normal
Answer and see the solution →(a)[2 marks]The diagram below shows the reaction profile for a chemical reaction without a catalyst.
Reaction profile diagram for a reaction without a catalyst. Draw on the diagram, using a dashed curve, how the reaction profile would look if a catalyst was used.
(b)[2 marks]Explain, using the diagram, how the catalyst affects the reaction.
Question 103
3 marks · Normal
Answer and see the solution →A reaction has reactants at an energy level of 95 kJ/mol, a peak (without a catalyst) at 155 kJ/mol, and products at 65 kJ/mol.
A catalyst provides an alternative pathway with a peak at 110 kJ/mol.
Calculate:
(a)[1 mark]The activation energy without a catalyst.
(b)[1 mark]The activation energy with a catalyst.
(c)[1 mark]The difference in activation energy caused by the catalyst.
Question 104
3 marks · Normal
Answer and see the solution →A student says: 'When you add a catalyst, more particles in the reaction mixture have the required activation energy to react.'
Explain, with reference to reaction profile diagrams, whether this statement is correct.
Question 105
4 marks · Normal
Answer and see the solution →The table shows energy values for a chemical reaction.
Description Energy (kJ/mol) Reactants 75 Peak without catalyst 142 Peak with catalyst 95 Products 45 (a)[1 mark]Calculate the activation energy for the uncatalysed reaction.
(b)[1 mark]Calculate the activation energy for the catalysed reaction.
(c)[1 mark]Calculate the overall energy change () for the reaction.
(d)[1 mark]State how the catalyst changes the reaction profile diagram.
Question 106
2 marks · Normal
Answer and see the solution →State two reasons why catalysts are important in industrial chemical reactions.
Question 107
4 marks · Normal
Answer and see the solution →Read the passage below and answer the questions that follow.
(a)[2 marks]Explain how a catalyst lowers the activation energy of a reaction.
(b)[1 mark]State what effect a catalyst has on the overall enthalpy change (ΔH) of the reaction.
(c)[1 mark]Does the catalyst get used up in the reaction? Explain your answer.
Question 108
3 marks · Normal
Answer and see the solution →The diagram below shows the energy changes in a reaction with and without a catalyst.
Reaction profile showing catalysed and uncatalysed paths. The activation energy for the uncatalysed reaction is 100 kJ/mol, and the activation energy for the catalysed reaction is 60 kJ/mol. The enthalpy change (ΔH) for the reaction is -40 kJ/mol.
Calculate the difference in activation energy between the catalysed and uncatalysed routes, and explain what effect this has on the rate of reaction.
Question 109
3 marks · Normal
Answer and see the solution →You are given an unknown white powder and asked to find out if it is a catalyst for the decomposition of hydrogen peroxide solution. Describe how you would show that this substance is a catalyst in the reaction.
Question 110
4 marks · Normal
Answer and see the solution →An industrial process uses iron as a catalyst for the reaction between nitrogen and hydrogen to form ammonia (the Haber process):
The data below show the percentage yield of ammonia at two different temperatures, with and without the iron catalyst.
Temperature/°C Catalyst present? Percentage yield of ammonia 400 No 15 400 Yes 15 500 No 10 500 Yes 10 Use the information in the table to answer the questions.
(a)[1 mark]Does the iron catalyst affect the percentage yield of ammonia at these temperatures? Explain your answer.
(b)[2 marks]Explain why the use of the iron catalyst is still important in this industrial process.
(c)[1 mark]Suggest one economic benefit of using a catalyst in the Haber process.