How do chemists use balanced equations?

Answer 1

To correctly determine the balanced chemical equation, one must make sure that the products are appropriately relating to the reactants and make sure that the equation is balanced with the lowest coefficients. That should help.

Answer 2

This is important for stoichiometry. So for example you can say that

H2 + O2 -> H2O. But it's actually not correct because there are two oxygens on the left and only one on the right. So the correct, balanced, equation is

2H2 + O2 -> 2H2O. Now there are four hydrogens on the left and right, and two oxygens on the left and right, so it is now balanced. This is important because you will need to know the balanced equation to do a lot of problems. It can help you determine concentration, mass, equilibirium, etc. But you can also say that 2 hydrogens and 1 oxygen will make 2 waters. Note that I said one oxygen, because even though it's O2, when chemists say oxygen, we assume you're talking about the diatomic oxygen (O2) because that's the most stable form.