Question

Q-1 How can we say that in a given change a chemical reaction has taken place? please write fast and full answer with explanation
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Answer 1

Answer:

The following observations in an activity may suggest that a chemical reaction has taken places.

∙ Change in state

∙ Change in colour

∙Evolution of a gas

∙ Change in temperature

(i) 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.

CaO(s)+H

2

O(l)→Ca(OH)

2

(aq)

ii) Also, when calcium carbonate is heated, it decomposes to form calcium oxide and carbon dioxide.

Here, evolution of the gas (carbon dioxide) confirms that a chemical reaction has taken place.

CaCO

3

→CaO+CO

2