Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Section
Why do reactions either give out or absorb heat?
19 practice questions
Practice questions
1–8 of 8 · Easy
Question 1
1 mark · Easy
Answer and see the solution →State what happens to energy when chemical bonds are formed.
Question 2
3 marks · Easy
Answer and see the solution →Methane reacts with oxygen as shown:
(a)[1 mark]State one bond broken in the reactants.
(b)[1 mark]State one bond formed in the products.
(c)[1 mark]Explain, using bond breaking and making, why this reaction releases heat.
Question 3
2 marks · Easy
Answer and see the solution →The equation below shows a reaction:
Bond Bond energy (kJ/mol) H–H 436 I–I 151 H–I 299 Calculate the overall enthalpy change (ΔH) for the reaction. State if it is exothermic or endothermic.
Question 4
2 marks · Easy
Answer and see the solution →Explain, in terms of bond breaking and bond making, why heating calcium carbonate is endothermic.
Question 5
3 marks · Easy
Answer and see the solution →The table shows average bond energies for some bonds:
Bond Bond energy (kJ/mol) C–C 348 C–O 358 O=O 498 Ethanol (C2H5OH) can be combusted in oxygen to form carbon dioxide and water. Use the data to answer the following:
(a)[1 mark]State which bond in the table requires the most energy to break.
(b)[1 mark]Complete the sentence: The combustion of ethanol is exothermic because the total energy released from making bonds is ____ than the energy needed to break bonds.
(c)[1 mark]Explain what the term 'average bond energy' means.
Question 6
1 mark · Easy
Answer and see the solution →What must occur to the bonds in a molecule for a reaction to absorb heat from the surroundings?
Question 7
3 marks · Easy
Answer and see the solution →The reaction below takes place:
Answer the following questions:
(a)[1 mark]State one bond broken during this reaction.
(b)[1 mark]State one bond formed during this reaction.
(c)[1 mark]Explain why energy is required for this reaction to occur.
Question 8
2 marks · Easy
Answer and see the solution →Hydrogen reacts with bromine to make hydrogen bromide:
Bond Bond energy (kJ/mol) H–H 436 Br–Br 193 H–Br 366 Calculate the enthalpy change (ΔH) for the reaction. Include units and sign.