A chemical reaction is when a reaction occurs that changes the make-up (basically what makes something that thing. For example you have chemical make-up that makes you you. If that make up changed then you wouldn't be you anymore) making what ever was reacted into a NEW product
For example digestion is a chemical reaction. Let's say that you eat a carrot. When digestion (the chemical reaction) is complete the carrot is no longer how it was when your first put it in your mouth. It has been broken down and the acid in your belly changed the chemical make up so that your body can use the carrot for energy
Now let's say that you shred a piece of paper. This is NOT a chemical reaction, because the shredded paper is still the paper it was before it was shredded
Hope this helped!
~Just a girl in love with Shawn Mendes