The burning of coal and the formation of water from hydrogen and oxygen are both classified under the same category of chemical reactions. Identify this category and state the single defining feature that justifies placing these two apparently different reactions together.
Generated by claude-sonnet-4-6 · 2026-06-26 00:54 · grounding rag
Model Answer
Category: Exothermic reactions.
Defining feature: In both reactions, heat (energy) is released to the surroundings during the reaction.
- Burning of coal: $\text{C} + \text{O}_2 \rightarrow \text{CO}_2 + \text{heat and light}$
- Formation of water: $\text{H}_2 + \text{O}_2 \rightarrow \text{H}_2\text{O} + \text{heat}$
Both release energy, making them exothermic.
Source: Chapter 1, Types of Chemical Reactions (What you have learnt)
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Explanation
- Examiners expect the category name (1 mark) and the defining feature — energy/heat released (1 mark).
- Writing a supporting equation is good practice but not compulsory for 2 marks; it strengthens the answer.
- Do not confuse with combustion (combustion is a type of exothermic reaction, not the broader category asked here). The question asks for the common classification, which is exothermic reactions.
- Key phrase to remember: "Reactions in which heat is given out along with the products are called exothermic reactions." (Chapter 1 summary)