Pornim de la 1mol de alcan
f.gen: CnH2n+2
raportul volumetric=raportul molar
1mol...........(3n+1)/2 moli...n moli
CnH2n+2 + (3n+1)/2 O2 -> nCO2 + (n+1)H2O
1mol...........(3n+1)/2...........n moli
n/(3n+1)/2=2n/3n+1=3/5
=> 10n=9n+3 => n=3
f.m: C3H8 - propanul