Explain how matter is not created or destroyed when there are chemical and physical changes.

When 2 different kinds of matter make contact, if they react to each other, they simply exchange atoms, not making any new matter in the process, they simply gets turned into something different.

Matter is neither created nor destroyed during a chemical or physical reaction but changes from one form to another, for example when we burn wood this is a chemical reaction by burning the wood we are not destroying it we are just changing it  to a different form which is charcoal,  also melting ice is a physical reaction here we are changing the ice from solid to liquid (water).