Here's why:

* Reactants: The substances that go into a chemical reaction.

* Products: The substances that are formed as a result of the reaction.

The process of a chemical reaction is essentially a transformation. Reactants are rearranged and/or combined to create new substances, the products.

Here are some other ways chemists might describe the relationship:

* Reactants yield products.

* Reactants are converted into products.

* Products are formed from reactants.

It's all about emphasizing the change that happens during the reaction.