formula alcanului CnH2n+2 , cu masa molara M= 14n+2.g/mol
ecuatia reactiei de ardere
CnH2n+2+ (3n+1)/2 O2---> nCo2 + (n+1) H2O
14n+2 g....................................................(n+1)x18g
2g.......................................................................3g
3x(14n+2)= 36(n+1)
42n+6= 36n+36---> 6n=30--> n=5 pentan