Question

How can a chemical equation be balanced?

Answer 1

Because mass is conserved in every chemical reaction.

Explanation:

If I start with 10 grams of reactant, from all sources, at most I can get 10 g of product. In practice, I am not even to get that. Chemical equations must reflect this mass balance, because the atoms and molecules that participate in the chemical reaction, have definite and measurable mass, and this mass will inevitably be conserved.