Brainliesttt ! how do you recognize substances that have gone through physical or chemical changes?

A chemical change turns a substance into something it was not before. Clues like light, heat, color change or the smell tell us if something has changed. The starting and ending process of the reaction is totally different. 

It produces a new substance. Example -  mixing HCl and NaOH to make salt and water. Another example is - when an ice cube melts to form water. In short, the only difference is its form. 

Good luck :)