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Question

Which of the following observation does not indicate a chemical change has occurred?

A
no new substances formed
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B
Evolution of gas
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C
Formation of new substances
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D
Change of odour
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Solution

The correct option is A no new substances formed

In a chemical change the chemical composition of the substance changes because of the formation of new substances.

Example:- Pb(NO3)2 (s) + Heat−− PbO (s) + SO2 (g) + SO3 (g)

The above example depicts a chemical change (chemical reaction) in which new substances are formed, gases evolve and change of odour is observed.

Change of physical state (Physical change) is a part of chemical change but this observation alone can't indicate that a chemical change has happened.

Example:- H2O(s) Heat−− H2O(l)

(Ice) (Water)

This is an example of a change of physical state (physical change) and no chemical change has happened here because the chemical composition of substance remains the same.


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