[Tensdale]

I have to calculate the balanced formula for gasoline; C8H18 (I know it's a extremely simplified formula) when it has been burned.

And I'm completely lost here. I have no idea how to calculate how much O is needed to calculate the difference between a complete and uncomplete combustion.
Do I just chose a number or?

EDIT: Okay, so I've sort of figured out how many O molecules I need.
I need 16 O to make CO2 out of the 8 carbon. And I need 9 O to make H2O out of the 18 H. So 25 in all. How do I write this? Because I'm pretty sure I need dioxygen. But I can't really write C8H18 + 12,5 O2.
And C8H18 + 25O, looks.... Off.

[Borek]

12.5O₂ is OK - at least during balancing. Final step is to change coefficients so that they become the smallest possible integers. In this case just multiply everything by 2, yielding 2C₈H₁₈ + 25O₂...

[Tensdale]

Ah, yes. That's what I forgot.

THANK YOU  

EDIT: Oh, wait. Before I forget, why exactly is it that I need dioxygen? Why will it not work with just 25O?

[Borek]

Oxygen (as several other gases - N₂, halogens) is present at STP as diatomic molecules.

[Tensdale]

And what does that mean in english?
(I'm being teached in another language, so if you don't spell it out for me, I have have no idea what you're talking about)

[XGen]

Instead of existing as singular O atoms, they exist as O₂ where the oxygen forms a double bond with another oxygen. This is how it occurs naturally.