3 C(s) + 2 Fe2O3(s) -4 Fe(s) + 3 CO2(g)

Why is it written as CO2 and not CO3?

Question

3 C(s) + 2 Fe2O3(s) ->4  Fe(s) + 3 CO2(g)

Why is it written as CO2 and not CO3?

accessdenied · Answer

If we assume the coefficients are correct for balancing the equation, the number of Oxygen on the left should match the number of Oxygen atoms on the right.
  So if you traded out CO2 for CO3, it no longer matches, right?  Test it out for yourself to see.  The coefficient on  2 Fe2 O3  applies to O as well as Fe,  so there are 2*3 = 6 Oxygen atoms on the left.

anonymous · Answer

I see. Thank you!

accessdenied · Answer

Glad to help!
And another tip, CO2 "carbon dioxide" is just a lot more common.  You might see CO as well, but carbon trioxide (no charge) is actually unstable and doesn't form under typical conditions.  :)