[Farhan0801]

Hi, so my teacher sent us a tutorial to do and one of the questions is to write down balanced chemical equation for complete combustion of compound Q where compound Q is butane. So I put my answer which is
2 C8H18 + 25 O2 -> 16 CO2 + 18 H20 but my teacher said it's wrong and the correct answer is
C8H18 + 25/2 O2 -> 8 CO2 + 9 H20 because the answer should always be the simplest form. This is very confusing for me and the whole class because last year my Chemistry teacher (which is different teacher than the one who gave the tutorial) strictly told us that we must multiply by 2 if we got a fraction in every balance complete combustion equation. So can anyone help me which one is the accurate/appropriate/correct answer.

Sorry for the bad english

[Borek]

I am not sure if one of the answers can be called "the correct one".

From what I remember IUPAC doesn't define precisely how the balanced reaction should look like. It is quite common to follow the convention of using the lowest natural numbers in balanced reaction equation, so I wouldn't call your answer wrong.

At the same time sometimes it is convenient to write reaction using fractional numbers. When you have a list of several alkanes writing their combustion reactions in such a way they all start with a single molecule (even if this means fractional coefficients of oxygen) makes comparisons (of amount of oxygen required, of molar combustion heat) easier.