To start, yours is too specific.. For example: when chemicals are mixed a chemical reaction will happen.
First off, what are considered to be chemicals? could i classify water and oil as a chemical? If i were to mix these two things then a chemical reaction would not occur.
You need to narrow your thought process more like your teachers, she mentions categories the chemical reactions are based under? How do you know a chemical reaction has occured?
You may want to address the basics of knowing when a chemical reaction has occurred before delving deeper and specifically stating that a chemical reaction happens only under these conditions