Write the complete balanced equation for the following reaction:
c5h9o + o2 yields co2 + h2o
, i'm lost : /

To complete the balancing of the following combustion reaction, we must do elemental balances. For C, there is 5 on the left side hence there should be 5 CO2. For H, H20 should be 9/2. Next we balance O. on theright side we find a total of 29/2. So the o2 on the left side should be 29/4. To  have whole number stoich.coeff. we multiply the numbers by 4, hence answer is
4C5H9O + 9O2= 20 O2 + 18 H20. 

The correct answer is "atomic weight".

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom.