Question

How would you balance the following equation: $Fe+O_2\to F{e}_2{O}_3$?

Answer 1

Step 1: Tally the number of atoms based on subscript.
$Fe+O_2\to F{e}_2{O}_3$ (unbalanced)
left side: $Fe=1;O=2$
right side: $Fe=2;O=3$

Step 2: Start balancing the simple molecules first, in this case the $O_2$
$Fe+3O_2\to F{e}_2{O}_3$
left side: $Fe=1;O=2\times 3=6$
right side: $Fe=2;O=3$

Since there are now $6O$ atoms on the left, there must also be $6O$ atoms on the right. Notice that the right hand is one big molecule so whatever coefficient we would use to balance the $O$ atoms, we would also need to apply to the bonded $Fe$ atom.

$Fe+3O_2\to 2F{e}_2{O}_3$
left side: $Fe=1;O=2\times 3=6$
right side: $Fe=2\times 2=4;O=3\times 2=6$

Step 3: Now balance the rest of the equation.
$4Fe+3O_2\to 2F{e}_2{O}_3$
left side: $Fe=1\times 4=4;O=2\times 3=6$
right side: $Fe=2\times 2=4;O=3\times 2=6$

The equation is now balanced.