The elements or compounds that enter into a chemical reaction are called reactants.

Here's a simple explanation:

* Reactants are like the ingredients in a recipe. They are the substances that are present at the beginning of a chemical reaction.

* Products are the substances that are formed as a result of the reaction. They are the "finished dish" after the chemical change has occurred.

For example, in the reaction of hydrogen gas (H₂) with oxygen gas (O₂) to form water (H₂O):

Reactants: H₂ and O₂

Products: H₂O

The chemical equation for this reaction is:

2H₂ + O₂ → 2H₂O

This equation shows that two molecules of hydrogen react with one molecule of oxygen to produce two molecules of water.