Question

List four observation that help us to determine whether a chemical reaction has taken place

Answer 1

The observations are
1 change in colour of products
2 Evolution of smell or odour
3 evolution of heat while the reaction is happening
4 Precipitation of products after the reaction is held...

Answer 2

Some observations can easily help to detect the occurrence of a chemical reaction;

Some of those observations are;

1)Change of the temperature.

2) Change of the mass.

3)Change of colour, physical state or smell.

4) Generation of noise.

(Although these observations can also happen for a physical change also)

And many more.