In a chemical change, reactants are the substances that go into a chemical reaction. They are the starting materials that will be transformed into new substances.

Think of it like baking a cake:

* Flour, sugar, eggs, butter, and milk are the reactants - they are the ingredients you start with.

* The cake is the product - the new substance created by the chemical reaction of baking.

Here's a more formal definition:

Reactants are the chemical species that are consumed during the course of a chemical reaction. They are represented on the left side of a chemical equation.

For example, in the reaction:

2H₂ + O₂ → 2H₂O

* H₂ (hydrogen gas) and O₂ (oxygen gas) are the reactants.

* H₂O (water) is the product.

The arrow in the equation indicates that the reactants are transformed into the product.