What is the weight of gas (car) vs carbon (as burn off)?

Question

I know a tank of gas could possibly weigh on a 13 gal tank approx 90 lbs. But when this is burned off what is the weight of the Carbon gas? When its burned off does it affect the weight of the earth? Does it just dissapate and leave earth (physical) (making earth weigh less) or just stay in air?

Answer 1

1 gallon of gas = 19 lbs of carbon dioxide (CO2) approximately. So your 13 gallon tank of gas will produce almost 250 lbs of carbon dioxide.

Gasoline consists of several different hydrocarbon molecules. A typical one to represent gasoline is octane. Octane has 8 carbon atoms and 18 hydrogen atoms. Carbon weighs about 6 times more than hydrogen and so the carbon accounts for about 72% of the weight of gasoline.

When you burn gasoline the octane molecule is ripped apart and each carbon is mated with two oxygen atom and each pair of hydrogens is mated with one oxygen atom. The combustion products of perfect burning then is eight carbon dioxide molecules and nine water molecules. We don't care about the weight of the water. But we are interested in the weight of the carbon dioxide. Oxygen is actually slightly heavier than carbon and we have added two oxygens for each carbon. So the weight of the carbon dioxide produced is quite a bit heavier than the original octane. It is 3.67 times heaver to be exact.

Burning it does not effect the weight of the earth because all that oxygen came from the atmosphere and so there is a little bit less of that keeping everything nicely balanced.

I suppose if you wanted to get extremely technical and include the effects of relativistic physics, you would have to take into account of the fact that energy and mater are two forms of the same stuff and by burning the gasoline you have released energy, which means that you converted an incredibly tiny amount of the mass to energy to make that energy and so technically the Earth is actually a very very tiny bit lighter.

Answer 2

The weight of the burned off gas is heavier than the tank of gas a lot heavier because the fuel molecules now contain oxygen. The weight of the earth is unchanged but the chemistry of the earth is changed.