Atoms don't just magically appear or disappear from the reactant or product
sides. The same amount of atoms needs to
be shown on both sides because of the:
The Law of Definite Proportions
The Law of Conservation of compounds
The Law of Conservation of Mass
The Law of Gravity

Law of the Conservation of Mass

Explanation:

During a chemical reaction, the mass of the reactants and products must be the same. The total number of atoms stays equal. Elements cannot magically appear or disappear in a reaction, so you have to account for all of them

answer; synapse;