Here's why:

* Law of Conservation of Mass: This fundamental law states that matter cannot be created or destroyed in ordinary chemical reactions. The total mass of the reactants (starting materials) must equal the total mass of the products (substances formed).

* Unbalanced Equation: An unbalanced equation shows an unequal number of atoms of each element on the reactant and product sides. This implies that atoms are being created or destroyed, which violates the Law of Conservation of Mass.

Example:

* Unbalanced: H₂ + O₂ → H₂O

* Balanced: 2H₂ + O₂ → 2H₂O

In the unbalanced equation, there are two hydrogen atoms and two oxygen atoms on the reactant side, but only two hydrogen atoms and one oxygen atom on the product side. This suggests that an oxygen atom disappeared, which is impossible according to the Law of Conservation of Mass. The balanced equation shows the correct number of atoms on each side, ensuring that the total mass remains constant throughout the reaction.