# Why do you need to balance a chemical equation?

Jul 22, 2016

A knowledge of basic arithmetic.

#### Explanation:

...And also a properly balanced chemical equation to establish stoichiometry. Mass is conserved in every chemical reaction. If I start with 10 g of reactant at most I can finish with 10 g of product. In practice, I am not even going to get that, because losses occur on handling.

We take a simple equation:

${H}_{2} \left(g\right) + \frac{1}{2} {O}_{2} \left(g\right) \rightarrow {H}_{2} O \left(l\right)$

This tells unequivocally that 2 g of dihydrogen reacts with 16 g of dioxygen to give 18 g of water. It is self evident that mass has been conserved, as it must be for stoichiometry.

So here's a job for you:

The following equation is balanced with respect to mass and charge,

$C {H}_{4} \left(g\right) + 2 {O}_{2} \left(g\right) \rightarrow C {O}_{2} \left(g\right) + 2 {H}_{2} O \left(l\right)$

If I burn 16 g of methane, (i) how many grams of dioxygen do I require; (ii) how many grams of carbon dioxide gas will be evolved?