How does 113 gallons of gasoline become a metric ton of carbon dioxide? [Alan]

One gallon of gasoline weighs 6.3 pounds.  One chemical formula for gasoline is C8H18.  This means the molecule is 8 Carbon atoms long with a Hydrogen everywhere it has a bond. We can visualize it thus:

Though it may form a ring.

Carbon has a mass of 12 while Hydrogen has a mass of 1.  Thus, the mass of this molecule is (8*12) + (18 * 1) = 210, of which 192 is carbon.  Thus, of the 6.3 pounds of gasoline in a gallon, 192/210ths (5.26 lbs) are Carbon and the rest is Hydrogen.  Now, when gasoline is burned, each carbon atom combines with two Oxygen atoms with their own mass of 16, so two Oxygen atoms have a mass of 32 and each Carbon atom, previously weighing in at 12, becomes one CO₂ molecule weighing in at (12 + 32) = 44. So, the 5.26 pounds of Carbon now become (5.26 * 44/12 = 19.31) lbs of carbon dioxide.  One ton is 2000 lbs.  So, the number of gallons required to produce a ton of is CO₂ is (2000/19.31) or 103.5 gallons.

Estimates from the web are variable, but fluctuate around 100 gallons – as Ray suggested.  This is probably because different sources use a different number of carbon atoms in the molecule and thus a different ration of C:H.