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How can six pounds turn into twenty pounds?

A gallon of gas weighs about 6.5 pounds but when that gallon is burned as fuel in your car you are adding about 20 pounds of carbon dioxide, a greenhouse gas, to the atmosphere.  This may seem counter-intuitive.  After all, how can six pounds end up being twenty pounds?  Enter chemistry…

A molecule of gasoline typically has eight carbon atoms in it (“octane”, shown here), along with eighteen hydrogen atoms.[lightbox link=”” thumb=”” width=”335″ align=”center” title=”octane” frame=”true” icon=”image” caption=””]

When gasoline is used as a fuel in your car it undergoes combustion, a chemical reaction where a fuel reacts with oxygen to give off heat or light (energy).  The gasoline does not disappear into thin air.  Instead, the carbon and hydrogen in gasoline separate from each other, their bonds vaporized.

The newly freed carbon atom then joins with two oxygen atoms to form carbon dioxide, CO(shown here).  The hydrogen bonds with oxygen to form water (H20).[lightbox link=”” thumb=”×102.jpg” width=”195″ align=”center” title=”co2″ frame=”true” icon=”image” caption=””]

Now to solve this question as to how six pounds can turn into twenty pounds, with help from the Periodic Table of the Elements.  The atomic weight (remember, the atomic number is at the top of the element and the weight is on the bottom) of carbon is twelve, oxygen is sixteen, and hydrogen is one.

Each individual gasoline molecule “weighs” (8 X 12) + (18 X 1) = 114 going into your gas tank.

Each carbon dioxide molecule “weighs” 12 + (16 X 2) = 44.

For every molecule of gasoline you burn, you are contributing 8 molecules of carbon dioxide to the atmosphere, for a total “weight” of 44 X 8 = 352.  Through combustion, the gas molecule that went into your tank at a “weight” of 114 are converted to 8 carbon dioxide molecules with a total weight of “352”, roughly 3 times (3.09)  the weight of the gasoline.

Take a gallon of gas at 6.5 pounds, multiply by 3.09, and you get 20.08…your six pounds turned into twenty!

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