What is a balanced chemical equation? How would you use the law of conservation of mass to explain why a chemical equation must be balanced?

Jun 12, 2016

In every chemical equation that has ever been performed, mass is CONSERVED. What does this mean?

Explanation:

Conservation of mass means that if I start with 10 g of reactant, from all sources, at MOST I can get 10 g of product. In practice, I am not even going to get that, because losses inevitably occur on handling. Since mass is a property of atoms and molecules, fundamental particles in other words, it follows that these masses are conserved during a chemical reaction.

Let's examine a simple(?) combustion reaction, that of pentane:

${\underbrace{{C}_{5} {H}_{12} \left(l\right) + 8 {O}_{2} \left(g\right) \rightarrow 5 C {O}_{2} \left(g\right) + 6 {H}_{2} O \left(l\right)}}_{\text{328 g of reactants yields 328 g of products}}$

Is this balanced? How do you know? If it is balanced, then there is mass equivalence of reactants, $328 \cdot g$ and products ??g.

All of this are examples of stoichiometry. Stoichiometry insists that mass (and atoms and molecules) be balanced with respect to mass and charge.

$\text{Garbage in must equal garbage out}$.

Note that we practise stoichiometry all the time, For instance when we make a cash or electronic transaction; debits and credits are balanced. If they are not, someone will very soon notice.