Question

Why do we have to balance equations with respect to mass?

Answer 1

You have not given a specific example, BUT EVERY CHEMICAL REACTION CONSERVES MASS.

Explanation:

This is why teachers insist that equations be stoichiometrically balanced. If we start with `10` `g` of reactant from ALL sources, AT MOST, we can get `10` `g` of product. In practice, we are not even going to get that, because loss will inevitably occur upon handling.