Pearson Edexcel International GCSE (9–1) · CHEMISTRY · Section
Why do reactions either give out or absorb heat?
19 practice questions
Practice questions
11–19 of 19
Question 11
3 marks · Normal
Answer and see the solution →The reaction below occurs:
Bond energies (in kJ/mol): H–H = 436, Cl–Cl = 243, H–Cl = 431
Calculate the overall enthalpy change (ΔH) for the reaction.
Question 12
3 marks · Normal
Answer and see the solution →Describe, using bond breaking and bond making, how you can tell if a chemical reaction will be exothermic or endothermic.
Question 13
4 marks · Normal
Answer and see the solution →The table below gives average bond energies.
Average bond energies Bond Bond energy (kJ/mol) C–H 413 O=O 498 C=O 799 (a)[2 marks]List the bonds broken and bonds formed when methane reacts with oxygen to form carbon dioxide and water.
(b)[2 marks]Suggest, using the bond energies, why this reaction is highly exothermic.
Question 14
1 mark · Normal
Answer and check →Which statement best describes what happens during bond formation in a chemical reaction?
- A.Energy is released to the surroundings.
- B.Energy is absorbed from the surroundings.
- C.The temperature always decreases.
- D.No energy change occurs.
Question 15
2 marks · Normal
Answer and see the solution →State what must occur, in terms of bonds, for a reaction to be endothermic.
Question 16
4 marks · Normal
Answer and see the solution →Read the following reaction:
You are given these average bond energies (kJ/mol): S=O = 523, O=O = 498
a) Write down all bonds that are broken and formed during the reaction.
b) Explain, using these bond energies, what determines whether the reaction is exothermic or endothermic.
(a)[2 marks]List all bonds broken and formed.
(b)[2 marks]Explain, using bond energies, what determines if the reaction is exothermic or endothermic.
Question 17
2 marks · Hard
Answer and see the solution →A reaction is found to be exothermic overall. Explain, in terms of bond energies, why this is the case.
Question 18
5 marks · Hard
Answer and see the solution →When carbon monoxide reacts with oxygen, the following reaction occurs:
You are given the following average bond energies:
Bond Average bond energy (kJ/mol) C≡O 1072 O=O 498 C=O (in CO2) 805 (a)[2 marks]List one type of bond broken and one type of bond formed in this reaction.
(b)[1 mark]Explain why this reaction is exothermic, using bond energies.
(c)[2 marks]Calculate the enthalpy change, ΔH, for the reaction, using the bond energies in the table. Show your working and give the answer in kJ/mol (for the equation as written).
Question 19
2 marks · Hard
Answer and see the solution →Describe, in terms of bonds and energy, what happens during an endothermic reaction.