3.4       recall the products of the complete and incomplete combustion of alkanes

·        In plenty of air (enough oxygen), alkanes burn completely to give water and carbon dioxide only.

Tips on balancing equations for combustion of alkanes (or any compound containing C, H and O):

1.      Balance C first – all the C in the compound ends up as CO2 on the right hand side.

2.      Balance H next – all the H in the compound ends up as H2O on the right hand side.

3.      Balance O last – add up all the O atoms on the right hand side, divide by 2 to give you the balancing number for the oxygen.

Example for propane burning is shown below:

C3H8(g)    +    5O2(g)    ®    3CO2(g)   +    4H2O(l)

Propane has 3 C atoms so the balancing number for CO2 is 3.

Propane has 8 H atoms so the balancing number for H2O is 4.

The total number of O atoms now on the right hand side is (3×2) + 4 = 10, so the balancing number for O2 on the left hand side is 5.

In limited air (insufficient oxygen), alkanes burn incompletely to give water and carbon monoxide and/or carbon (soot).  Carbon monoxide is very poisonous