In a balanced chemical equation, what must be equal on both sides?

In a balanced chemical equation, the fundamental principle is that the law of conservation of mass must be upheld. This means that the number of atoms of each element present in the reactants must equal the number of atoms of that element present in the products.

When balancing an equation, coefficients are adjusted to ensure that each type of atom is accounted for equally on both sides of the equation. This reflects the conservation of matter; atoms cannot be created or destroyed during a chemical reaction, only rearranged. For example, if you have two hydrogen atoms and one oxygen atom on the reactant side, you must have the same number of hydrogen and oxygen atoms on the product side, typically represented as two water molecules (2H₂O) to balance the equation.

While the total mass of substances, energy, and the number of molecules involved in the reaction are important considerations in chemistry, they do not specifically define what must be equal in a balanced chemical equation. The correct principle focuses on ensuring that the count of each specific atom type remains the same before and after the reaction, thus satisfying the requirements of a balanced equation.