The type of equation that describes a chemical reaction where the number of atoms of each element is the same on both sides, and mass is conserved, is called a balanced chemical equation.

Here's why:

* Conservation of Mass: The fundamental principle behind balanced chemical equations is the Law of Conservation of Mass. This law states that matter cannot be created or destroyed in a chemical reaction. Therefore, the total mass of the reactants (starting materials) must equal the total mass of the products (substances formed).

* Balancing the Equation: To ensure mass conservation, we use coefficients (numbers in front of each chemical formula) to balance the number of atoms of each element on both sides of the equation. This process is called balancing the chemical equation.

Example:

The reaction of hydrogen gas (H₂) with oxygen gas (O₂) to form water (H₂O):

Unbalanced: H₂ + O₂ → H₂O

Balanced: 2H₂ + O₂ → 2H₂O

Explanation:

* In the unbalanced equation, there are 2 hydrogen atoms and 2 oxygen atoms on the reactant side, but only 2 hydrogen atoms and 1 oxygen atom on the product side.

* By adding a coefficient of 2 in front of H₂O, we now have 4 hydrogen atoms and 2 oxygen atoms on both sides of the equation. This ensures that the same number of atoms of each element are present on both sides, satisfying the Law of Conservation of Mass.