How would you balance the following equation: Fe+O2 --> Fe2O3?

Nov 2, 2015

$4 F e$ + $3 {O}_{2}$ $\rightarrow$ $2 F {e}_{2} {O}_{3}$

Explanation:

Step 1: Tally the number of atoms based on subscript.

$F e$ + ${O}_{2}$ $\rightarrow$ $F {e}_{2} {O}_{3}$ (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 ${O}_{2}$

$F e$ + $\textcolor{g r e e n}{3} {O}_{2}$ $\rightarrow$ $F {e}_{2} {O}_{3}$

left side: Fe = 1; O = 2 x $\textcolor{g r e e n}{3}$ = 6
right side: Fe = 2; O = 3

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

$F e$ + $3 {O}_{2}$ $\rightarrow$ $\textcolor{red}{2} F {e}_{2} {O}_{3}$

left side: Fe = 1; O = 2 x 3 = 6
right side: Fe = 2 x $\textcolor{red}{2}$ = 4; O = 3 x $\textcolor{red}{2}$ = 6

Step 3: Now balance the rest of the equation.

$\textcolor{b l u e}{4} F e$ + $3 {O}_{2}$ $\rightarrow$ $2 F {e}_{2} {O}_{3}$

left side: Fe = 1 x $\textcolor{b l u e}{4}$ = 4; O = 2 x 3 = 6
right side: Fe = 2 x 2 = 4; O = 3 x 2 = 6

The equation is now balanced.