Question

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?

Answer 1

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_5H_12(l) + 8O_2(g) rarr 5CO_2(g) + 6H_2O(l))_"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*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.

`"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.