The mass in a chemical reaction is not found in a specific location. Instead, it is conserved, meaning that the total mass of the reactants (the starting materials) equals the total mass of the products (the substances formed).

This principle is known as the Law of Conservation of Mass, which was first proposed by Antoine Lavoisier.

Here's what happens:

* Atoms are rearranged: In a chemical reaction, atoms are not created or destroyed, they are simply rearranged into different combinations.

* Mass is conserved: Since the atoms themselves are not changing, the total mass of the system remains constant throughout the reaction.

Example:

Imagine burning wood in a fire. The wood (reactant) reacts with oxygen (reactant) to produce ashes, carbon dioxide, and water (products). While the appearance changes drastically, the total mass of the reactants (wood + oxygen) will be equal to the total mass of the products (ashes + carbon dioxide + water).

Important Note: While the total mass is conserved, the mass of individual substances may change. For example, in the burning wood example, the mass of the wood decreases as it is consumed, while the mass of the ashes, carbon dioxide, and water increases.