How do you balance #Fe + Cl_2 -> FeCl_3#?
You balance it stoichiometrically. Garbage in equals garbage out.
If you don't like the non-integral stoichiometric coefficient, you are free to double the entire equation:
Both equations are PRECISELY the same. They represent the same mass transfer. The first equation may be a little easier to use if you had to work the quantities of gas required for iron oxidation.