# Complete/Incomplete combustion?

(AQA) When you construct an equation of an alkane with n carbon atoms, how do you know how much oxygen moles there are, like if its 8 1/2O2

eg
C11H24 + ?O2 --> 8Co + 9H20

use equation CxHy + x+(y/4) O2 goes to xC02 + y/2 H20
x = no. of carbon atoms
y = no of hydrogen atoms
example

C2H6 (ethane) + 3.5 O2 - 2C02 + 3H20
i hope that helps good luck
when you go about balancing an equation, there's a method you use, eg. by balancing all the Carbon atoms 1st, or Oxygen, etc... does anyone know which order you do this in? thanks.
The order that I believe is best is Carbons, Hydrogens and then Oxygens (Steps [1], [2] and [3])

For example, let's use pentane:

Complete: C5H12 + 802 --> 5CO2 + 6H20

Incomplete: C5H12 + 5.502 --> 5CO + 6H20

So, first write out your hydrocarbon + 02 and then write CO2/CO +H20 according to whether it is complete or incomplete combustion (the products will never be different).

On the right hand side of the equation, there is only place with carbons, so you have no choice but to directly balance it with the left hand side. Therefore, if you have C5H12 on one side, you will have to put 5CO(2) on the other.

The same rule applies with the hydrogens. There is only one place for them on either side, so you can balance them directly. C5H12 must balance with 6H20.

Thus, we leave the oxygens until last in order to make them easier. The way to do it is just to add up how many oxygens you have on the right hand side (in this case, 16 for complete, 11 for incomplete) and then balance that with the O2 on the left hand side of the equation by dividing the number of oxygens on the right by 2 (because you have 02).

It's simple once you know what you're doing
thanks! :-)
thanks everyone!
Hey lol to anyone reading this in 2019 maybe you're a GCSE student or whatever haha like me rnThis guy has got the incomplete combustion thing wrong- i dunno where he got the 5.5 thing from with the left hand side- remember guys BALANCE THE EQUATION, it may take a while if you don't know what you're doing but just give it a go.Anyways here's the right answer for incompletealways ensure same amount is on both sides of the arrow)Incomplete: C5H12 5O2 --> 2CO CO2 6H2O C2
Original post by lane_in_pain
Hey lol to anyone reading this in 2019 maybe you're a GCSE student or whatever haha like me rnThis guy has got the incomplete combustion thing wrong- i dunno where he got the 5.5 thing from with the left hand side- remember guys BALANCE THE EQUATION, it may take a while if you don't know what you're doing but just give it a go.Anyways here's the right answer for incompletealways ensure same amount is on both sides of the arrow)Incomplete: C5H12 5O2 --> 2CO CO2 6H2O C2

what, that equation is such a mess, you produce carbon monoxide not carbon dioxide in incomplete combustion