Question

How to know chemical reactions?

Answer 1

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We can know a chemical reaction has taken place when :

♂A new substance is formed.

♂Hydrogen gas is released .

♂A smell can be smelt.

♂Change in state.(from solid to liquid or solid To gas ,etc.)

Answer 2

Because you can't see this exchange of atoms ,you must look for changes in physical properties to determine if a chemical reaction has occured.

1. Colour changes.A change in colour often indicates a chemical change.
2. Temperature changes.
3. Precipitates.
4. Light emission.
5. Gas production