Question

Answer the following in detail:
11. State any two observations in an activity suggesting the occurrence of a chemical reaction.
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Answer 1

• In an activity, change in state and change in temperature indicate that a chemical reaction has taken place: eg. Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.

Answer 2

Answer :  A chemical change can be confirmed by any of the following observations:

Change in temperature

Evolution of gas

For example: Calcium oxide reacts vigorously with water to produce calcium hydroxide. During this process, a large amount of heat is also evolved, which increases the temperature of the system. This confirms that a chemical reaction has taken place. Also, when calcium carbonate is heated, it decomposes to form calcium oxide and carbon dioxide. In this reaction, calcium carbonate breaks down to form calcium oxide and carbon dioxide. Here, evolution of the gas (carbon dioxide) confirms that a chemical reaction has taken place

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