How many Litres of fuel per metre of air?

Question

Lets just say, That the formula for burning fuel (heptane in this case) is,
C7H16+11(O2)>7(CO2)+8(H2O)
Air wieghs 1.2kg per cubic metre
it is 23% O2 by mass
Heptane is 679.5g per litre

Answer 1

I take it the question should read "... per cubic metre of air".

Weight of O2 = 0.23 (1.2) = 0.276 kg.
So n(O2) = 276 / 32.0 = 8.62 mol.
n(C7H16) = n(O2) / 11 = 8.62 / 11 = 0.784 mol.
m(C7H16) = n(C7H16) * (7(12.0) + 16 (1.0))
= 0.784 (100.0) = 78.4 g.
So the volume of heptane required is 78.4 / 679.5 = 0.12 L.