Q1. [2] medium initial-understanding
Burning of coal can be represented as C + O₂ → CO₂, and hydrogen reacting with oxygen produces water (2H₂ + O₂ → 2H₂O). What type of chemical reaction do both of these represent, and what common feature of the two reactions leads you to this classification?
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
Both reactions — C + O₂ → CO₂ and 2H₂ + O₂ → 2H₂O — represent combustion reactions, which are a type of oxidation (exothermic) reaction.
Common feature: In both reactions, a substance (carbon/hydrogen) combines with oxygen and releases heat and light energy. This gain of oxygen by the substance is called oxidation, making both reactions exothermic combustion reactions.
Source: Chapter 1 (Types of Chemical Reactions); Chapter 4, Section 4.3.1 (Combustion)
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Explanation
- Examiners expect students to name the reaction type correctly — combustion/oxidation — for 1 mark.
- The second mark is for identifying the common feature: both involve combination with oxygen, releasing heat and light (exothermic).
- Avoid writing just "combination reaction" — combustion is the specific and more accurate term here; also note it is a type of oxidation.
- Mentioning "heat and light released" strengthens the answer.