Endothermic example?
- combustion
- thermal decomposition
- neutralisation
- respiration
Show answer and explanation
Answer: B. thermal decomposition
Needs heat.
O Level Chemistry: Energy changes, questions with answers
Practise 19 real questions on Energy changes from 2021 to 2026. See the answer and explanation as soon as you answer.
19real questions
10multiple choice
10exam sessions
About Energy changes in O Level Chemistry
Energy changes is one of the 12 main topics in our O Level Chemistry (Cambridge (CAIE) 5070) question bank, and about 3% of its real questions come from it. Tayyari Karo has 19 real questions on this topic from 2021 to 2026, from Paper 1, Paper 2, Paper 3, Paper 4; 10 are multiple choice and marked instantly, and the rest are structured questions with a model answer. By difficulty: 16 medium, 2 hard, 1 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
Try 6 real questions
These are real past-paper questions. Think of your answer first, then open the explanation.
Some bond energy data (kJ/mol) are given: O-O 150, O=O 496, O-H 460, N-H 390, N-N 160, N=N 410, N#N 944, H-H 436. Hydrazine, N2H4 (structure H2N-NH2), reacts with oxygen: N2H4 + O2 -> 2H2O + N2. What is the value of the enthalpy change, ΔH, of this reaction, calculated using this bond energy data?
- -728 kJ/mol
- -568 kJ/mol
- -34 kJ/mol
- +352 kJ/mol
Show answer and explanation
Answer: B. -568 kJ/mol
Breaking one N-N bond, four N-H bonds and one O=O bond needs 160 + 1560 + 496 = 2216 kJ/mol, while forming four O-H bonds and one N#N bond releases 1840 + 944 = 2784 kJ/mol, giving ΔH = 2216 - 2784 = -568 kJ/mol.
Respiration is
- endothermic
- exothermic
- photochemical
- reversible
Show answer and explanation
Answer: B. exothermic
Releases energy.
Endothermic =
- releases heat
- absorbs heat
- no energy change
- gives light
Show answer and explanation
Answer: B. absorbs heat
Absorbs heat.
Burning methane is
- endothermic
- exothermic
- photochemical
- reversible
Show answer and explanation
Answer: B. exothermic
Combustion releases heat.
Which is exothermic?
- thermal decomposition
- electrolysis
- combustion
- melting
Show answer and explanation
Answer: C. combustion
Burning releases heat.
Sessions with Energy changes questions
| Session | Paper 1 | Paper 2 | Paper 3 | Paper 4 |
|---|---|---|---|---|
| May/June 2026 | 1 | 1 | – | – |
| May/June 2025 | 1 | – | – | – |
| Oct/Nov 2025 | 1 | 1 | 1 | 1 |
| May/June 2024 | 1 | 1 | – | – |
| Oct/Nov 2024 | 1 | – | – | – |
| May/June 2023 | 1 | 1 | – | – |
| Oct/Nov 2023 | 1 | – | 1 | 1 |
| May/June 2022 | 1 | – | – | 1 |
| Oct/Nov 2022 | 1 | – | – | – |
| Oct/Nov 2021 | 1 | – | – | – |
Common questions
What does the Energy changes topic cover on this page?
19 real O Level Chemistry (5070) questions on Energy changes from 2021 to 2026, from Paper 1, Paper 2, Paper 3, Paper 4. Each one shows the year, session and paper it came from.
Do I get the answers and explanations?
Yes. Every question shows the correct answer and a short explanation the moment you answer.
Is it free?
You can start free with no signup. A small set of papers per subject is free, and Premium unlocks every paper, the full question bank and the paper PDFs.