Why do we get 20 lbs of co 2 from 1 gal of gas which weighs 6 lbs?

Question

Why do we get 20 lbs of co 2 from 1 gal of gas which weighs 6 lbs?

Answer 1

Gasoline is basically CH3-(CH2)n-CH3.  To a good approximation, the mass associated with each C is that of CH2 or 14 amu.  When the gasoline burns, the equation is

CH2 + 3/2 O2 -> CO2 + H2O.  The mass of CO2 is 44 and the mass ratio is approximately 44/14.  The extra mass comes from atmospheric oxygen.

Answer 2

The carbon in the gasoline combines with oxygen in the air to produce CO2.  As the oxygen atoms are heavier than carbon atoms, the resulting CO2 is heavier than the gasoline used to produce it.

Answer 3

So to folllow on that, since O isn't a greenhouse gas, we're really talking about C, not CO2, so we're not talking about 20 lbs.

Answer 4

Because gas and CO2 aren't the only things in the chemical reaction. The 6lbs of gas react (burn) with 20lbs of oxygen to produce 20lbs of CO2 and 6lbs of water. So air and gas go into your engine and CO2 and water vapor come out your tail pipe (thats why you sometimes see water dripping out of the tail pipes of large SUVs).