# Question #039d5

Nov 11, 2016

If I understand you would try just to balance mulecular masses.
It woul be right, but not sufficient to balance the reaction because it would give just one constraint on coefficients (you need several)

#### Explanation:

Example
$2 {H}_{2} O = 2 {H}_{2} + {O}_{2}$

We start from
$a {H}_{2} O = b {H}_{2} + c {O}_{2}$

Then realize that we can multiply both terms for a constant so we can put $a = 1$

Then equal the molecular masses:

$2 + 16 = b \cdot 2 + c \cdot 32$
$b = 9 - 16 c$

This is true in our balanced equation (where $a = 1 , b = 1 , c = \frac{1}{2}$), but not sufficient to find b and c.