Q1. [2] medium initial-understanding
When calcium oxide is added to water, the resulting mixture feels hot to the touch. What does this tell you about the nature of the reaction, and what term is used to describe such reactions?
Generated by claude-sonnet-4-6 · 2026-06-26 00:53 · grounding rag
Model Answer
The mixture feeling hot indicates that heat is released during the reaction. This tells us the reaction is exothermic in nature.
$$\text{CaO}(s) + \text{H}_2\text{O}(l) \rightarrow \text{Ca(OH)}_2(aq) + \text{Heat}$$
Reactions in which heat is released along with the formation of products are called exothermic reactions.
Source: Chapter 1, Section 1.2.1 Combination Reaction
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Explanation
- 1 mark for identifying the reaction as exothermic and stating that heat is released.
- 1 mark for correctly using the term "exothermic reaction" and defining it.
- The equation is a bonus touch that shows understanding, but the definition is what earns marks.
- Remember: this reaction is both a combination reaction (CaO + H₂O → one product) and an exothermic reaction — the question asks specifically about the heat aspect, so focus on exothermic.