How can you decide if a reaction is a Chemical reaction?

Answer 1

Chemical change is when the composition of your elements or solution change. In a simple way to say it, it's when you no longer have the same elements or solution that you started with.

You can determine if a reaction is chemical, by observing the chemical properties. Usually it's when there's a color change, a new substance formed, etc..

On the other hand, physical change is when the composition of your substance stay the same, but the physical properties change. For example, liquid water evaporate into H2O gas.