How do i balance this equation? C8H18 +O2 -> CO2 + H2O

Question

and then you must calculate mass of CO2 produced when 100g octain undergoes complete combustion.

Answer 1

The best way to balance this equation is to evaluate each atom on the reactants compare the amount of moles of products. Ex: C₈H₁₈ + O₂ --> CO₂ + H₂O

                    C-8                   C-1

                    H-18                 H- 2

                    O-2                   O- 3

You can see that the equation is unbalanced, so you just add a number in front of each atom until the whole equation is balanced. I want to try and balance the carbons first, but keep in mind that whatever number you put will also affect hydrogen and oxygen. So, I put an 8 on the product side.

Ex: C8H18 + O2 --> 8 CO2 + H2O

 

     C-8                    C-8
     H-18                  H- 2
     O-2                    O- 17

The equation is still not balanced that means that 8 in front of carbon is wrong, so I try another number until the whole equation is balanced.

Balanced equation: 2 C8H18 + 25 O2 --> 16 CO2 + 18 H2O

 

To calculate the mass of CO2 you will have to use the 100 g of octane and convert it to the mass of CO2 by including the moles and mass of the balanced equation given. 

100 g C₈H₁₈ x 1 mol C₈H₁₈ x 16 mol CO₂ x 44 g CO₂ = 308.8 g CO₂

                    114 g C₈H₁₈     2 mol C₈H₁₈  1 mol CO₂

              (Molecular weight)