Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Section
Exothermic reactions
19 practice questions
Practice questions
11–19 of 19
Question 11
3 marks · Normal
Answer and see the solution →Describe how the energy profile diagram of an exothermic reaction differs from that of an endothermic reaction. Your answer should refer to the relative positions of reactants and products and the direction of energy change.
Question 12
4 marks · Normal
Answer and see the solution →The table shows temperature changes observed in four different reactions:
Temperature changes in different reactions Reaction Temperature change (°C) A: Displacement reaction +16 B: Dissolving ammonium chloride -8 C: Combustion of butane +22 D: Neutralisation reaction +7 (a)[2 marks]Identify the two exothermic reactions.
(b)[2 marks]Explain your answer.
Question 13
1 mark · Normal
Answer and check →Which statement about the energy profile diagram for an exothermic reaction is correct?
- A.The products are at a higher energy level than the reactants.
- B.The activation energy arrow points downward from products to reactants.
- C.The reactants are at a higher energy level than the products.
- D.The energy change, ΔH, is positive.
Question 14
2 marks · Normal
Answer and see the solution →The reaction between magnesium and dilute hydrochloric acid is exothermic.
State what you would observe if you held the test tube during this reaction. Explain your answer.
Question 15
4 marks · Normal
Answer and see the solution →The energy profile diagram below represents an endothermic reaction.
Energy profile for an endothermic reaction (a)[2 marks]Label the diagram with:
(i) The activation energy (Ea).
(ii) The enthalpy change (ΔH).
(b)[2 marks]Explain why the reaction shown is endothermic.
Question 16
3 marks · Normal
Answer and see the solution →A student investigates three different reactions in identical test tubes. She measures the temperatures before and after each reaction:
Temperature changes for three reactions Reaction Initial temperature (°C) Final temperature (°C) A 21.0 34.0 B 20.5 15.8 C 22.0 21.7 Which of these reactions is exothermic? Calculate the temperature change for each reaction to justify your answer.
Question 17
2 marks · Hard
Answer and see the solution →Hydrogen peroxide can be decomposed to form water and oxygen gas. When manganese(IV) oxide is added to hydrogen peroxide solution in a test tube, you notice that the sides of the test tube become noticeably warmer.
Explain, in terms of energy transfer, why this reaction is classified as exothermic.
Question 18
5 marks · Hard
Answer and see the solution →The decomposition of a certain substance is shown by the energy profile diagram below.
(a)[0 marks]Energy profile diagram for a chemical reaction; energies in kJ/mol (b)[2 marks]State whether this reaction is exothermic or endothermic, and explain your answer using the energy values from the diagram.
(c)[2 marks]Calculate the value of ΔH (in kJ/mol) for this reaction using the energy profile diagram.
(d)[1 mark]The activation energy for the reaction is the energy difference between the reactants and the highest point on the diagram. Use the diagram to state the value of the activation energy for this reaction.
Question 19
2 marks · Hard
Answer and see the solution →A student says that 'all reactions which produce heat and raise the temperature are exothermic.' Give one example of a reaction that is exothermic, and explain how the energy changes in this type of reaction.