Hydrocarbons (of all stamps) react with oxygen to give CO_2 and H_2O. Sometimes the carbon in hydrocarbons, where oxygen is limited, react to give particulate C, and gaseous CO (this occurs particularly in diesel engines). Balance the carbons (as CO_2 for complete combustion), then the hydrogens (as water), and then the oxygen reactant (it doesn't matter if I have a half coefficient, because I could remove it by doubling the entire reaction:
2C_4H_10(g) + 13O_2(g) rarr 8CO_2(g) + 10H_2O(g)
For every reactant particle is there a corresponding product particle? Hmm, 8C's, 20H's, 26O's. So this equation is indeed stoichiometrically balanced, as required.
You should try this routine with other hydrocarbons, CH_4, H_3C-CH_3, hexane, kerosene, diesel. These questions invariably appear on A level exams, and with a little bit of preparation they are trivial exercises. Good luck!
