Question detail
Which of the following reactions is likely to be exothermic?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Energetics
Question
- A. Combustion of methane
- B. Dissolving ammonium nitrate in water
- C. Photosynthesis
- D. Decomposition of calcium carbonate
Answer
Combustion of methane
Explanation
The correct option is Combustion of methane. Combustion of methane is the best answer because it directly supports the AQA A-Level Chemistry objective to distinguish exothermic and endothermic reactions using enthalpy change signs. This reasoning is anchored to Enthalpy change in Energetics, and it separates enthalpy from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.
Common mistake
Confusing Exothermic and Endothermic Reactions
Students often confuse exothermic and endothermic reactions, thinking both release energy.
Exothermic reactions release energy to the surroundings, resulting in a negative enthalpy change (ΔH < 0), while endothermic reactions absorb energy, leading to a positive enthalpy change (ΔH > 0). To distinguish between them, remember that exothermic reactions feel hot (like combustion), whereas endothermic reactions feel cold (like photosynthesis).
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