Question

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1 How can we say that in a given change a chemical reaction has taken place?
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Answer 1

There are four signs that a chemical reaction has occurred: a change in color, a change in temperature, formation of a gas or formation of a precipitate.

Answer 2

Answer:

The presence of any of the following changes helps us to determine that a chemical reaction has taken place.

(i) Formation of new substance(s)

(ii) Change in state

(iii) Change in colour

(iv) Change in temperature, etc.