What is the weight ratio of CO2 released to fuel burned?

Full question: In several recent articles, reference was made to the amount of carbon dioxide (CO2) released from burning some quantity of fuel. It seemed that the tons of CO2 exceeded the weight of the fuel. What is the ratio of CO2 released to fuel burned by weight?

Susan Trumbore, professor in and chair of the earth system science department at the University of California, Irvine, calculates an answer to this question.

This seems like a question about conversion of mass to moles. (A mole is a unit of measurement to quantify the amount of a substance made up of atoms, where one mole is equal to 6.02 x 1023 units of that substance; 6.02 x 1023 is a chemical constant known as Avogadro's number.)

When considering fuel, let's take the example of gasoline. One of the primary components of gasoline is octane, which is made up of molecules that have eight carbon atoms and 18 hydrogen atoms. The weight of one mole of octane molecules will be equal to the summation of the weights of eight carbon atoms (at 12 grams/mole each, from carbon's mass number) plus 18 hydrogen atoms (at 1 gram/mole each). So, doing the math (8 x 12 + 1 x 18), we see that octane weighs 114 grams/mole.

If you combusted all of the octane to carbon dioxide, each of the eight carbon atoms would become part of a CO2 molecule. Thus, you would have eight CO2 molecules per octane molecule burned--or eight moles of CO2 per mole of octane burned. The weight of CO2 is 44 grams per mole (1 x 12 grams/mole for the carbon and 2 x 16 grams/mole for the oxygen atoms). Burning one mole of octane (114 grams), therefore, would produce eight moles of CO2, with a weight of 352 grams (8 x 44).

Thus, the weight ratio of CO2 produced per octane molecule burned is 352/114, or roughly 3 to 1.

Actual weight ratios will of course vary, since gasoline is not purely octane. In general, however, when you burn carbon fuels they are in "reduced" form, that is, the carbons in the molecules are attached mostly to hydrogen atoms. When they are burned, the carbon becomes "oxidized" (literally, combined with oxygen) to make CO2. Since oxygen is far heavier than hydrogen, the product is heavier than what is burned.

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1. 1. jbairddo 05:03 AM 2/13/08

Thank god, I asked the same question to the folks at Popular Science but apparently they were too busy to help or not smart enough to do so.

2. 2. Dan Confer 01:34 PM 2/13/08

So that means everything we burn effects the environment with the exception that the more efficient machine will get the job done by burning less; gas, flower, corn husks or whatever?

3. 3. count210 03:34 PM 2/13/08

What happens to the hydrogen? This is like drinking beer. One pound of beer adds two pounds to your body.

4. 4. DennisS 04:06 PM 2/13/08

There are no exceptions. If you burn (oxidize) any carbon based molucule you release CO2 (oxisized carbon),
The hydrogen also combines with oxygen and becomes H2O a.k.a. water

5. 5. adimitrov 09:27 PM 2/13/08

The point being - the extra weight comes from OUTSIDE - the atmospheric oxygen that combines with C and H. Same thing with beer - you may gain 2lb from drinking 1lb beer, but it's because the beer reacts with other things (I guess - water) and the retained portion has more weight than the original. Conservations of mass/energy makes sure that matter is not created out of nothing.

6. 6. r.c.dohare 10:13 AM 5/22/08

very good analysis presented this would be helpful to reduced CO2 emmission to atmosphere by efficient burning of fuel.by rcdohare25@yahoo.co.in

7. 7. zachary66 08:25 PM 11/18/08

I have ben working on a science fair project relating to this subject. I have worked out an ratio that shows: for every gallon of gassoline burned you get 17.8 pounds of co2, please dispute if I am wrong.

8. 8. clark 04:58 PM 7/20/09

Here you can calculate how much co2 your cardriving produce.
It is a Danish webpage
first you select how many km you drive every year
then you select how many km yor car drive pr. l gasolin
then you push the button bereng and you have the calculation

http://www.netbiologen.dk/asp/co2.asp

9. 9. tobyw276 08:42 PM 8/3/09

32 grams of oxygen (molecular wt. of 16 x 2 atoms) to every 12 grams of carbon (molecular wt. of 12) that you burn.

10. 10. Shajan 11:44 PM 1/12/10

What is the qty of co2 emission when 1 MT of furnace oil is burnt. Furnace oil is the heavy fraction and it contains 3 % sulphur.

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