Here's a breakdown:

* Reactants: These are the starting materials in a chemical reaction. They are the substances that will be transformed.

* Products: These are the new substances formed as a result of the chemical reaction. They are the outcome of the transformation.

In a chemical reaction, the atoms of the reactants are rearranged to form new molecules, which are the products. This rearrangement involves breaking and forming chemical bonds.

Example:

* Reactants: Hydrogen gas (H₂) and Oxygen gas (O₂)

* Reaction: Burning (combustion)

* Products: Water (H₂O)

Key point: The total number of atoms of each element remains the same on both sides of the chemical equation (reactants and products). This is known as the Law of Conservation of Mass.