Hi There I didn’t pay much attention in sciences classes I am afraid.
But some one should be able to help me out.
I try to live as consciously as possible and deal with the environment and CO2 emissions. But one thing always stays with me: The volume of CO2.
People always talk about kg CO2 per… For example: diving 5 km in a average car would emit 1kg of CO2. I drive a Toyota Aygo, so a little less then average, but lets say could drive around 20km on 1 litre of fuel. That would mean I’ll use around 0,25 litre for 5 km.
Typical E10 fuel weighs around 0,85kg per litre. That should mean I used around 212 grams of fuel to produce 1kg of CO2. That math doesn’t count up for me… Where does the other 788 grams come from?
In: 8
The fuel is iso-octane, so it has a chemical formula of C8H18. In order for the reaction to produce CO2, you need something with oxygen molecules.
The combustion reaction is fuel + oxygen -> CO2 + H2O. If you balance that reaction, it should help you figure out where all the mass is going
Oxygen. Each molecule of CO2 has 1 atom of carbon (which will come from the CHCHCHCH hydrocarbon chains in your fuel), and 2 atoms of O2 coming from the air that your engine takes in during the combustion.
The air.
Carbon has 12 AMU per atom, Oxygen has 16 AMU per atom.
Say you have a chunk of fuel that is mostly pure carbon. For simplicity sake.
When you burn that pure carbon, it combines with oxygen in the air to form CO2. So using the numbers in your example. You have 0.2 KG of carbon fuel, combining with 0.8 kg of oxygen in the air, to form 1.0 kg of CO2
CO2 is only 27% Carbon. The other 73% is oxygen which comes from the air that the fuel is burned in.
Not sure how to get the 5-to-1 fuel-to-CO2 ratio that you describe, but I can imagine close to 4-to-1 when completely burning pure coal.
Conventional fuels are hydrocarbons, some combination of carbon (C) and hydrogen (H) atoms in a chain or ring.
When you burn these, oxygen (O) molecules in the air jump in too to create carbon dioxide (CO2) and water (H2O)
Your final emissions will weigh more than the fuel consumed because a chemically equivalent amount of oxygen gas is also consumed to make the final product.
Correct answer already given, so I’ll try an analogy – as a chef, I can take a couple of egg whites of x volume, add nothing but energy (elbow grease whisking) and end up with 10x of volume – not magic, simply incorporating another substance to the mix.
CO2 forms when fuel reacts with oxygen from the atmosphere. Fuel mostly consists of hydrocarbons which, in turn, consist mostly of carbon and hydrogen. When it burns, hydrogen forms H2O (water) and carbon forms CO2.
However, 1 kg of CO2 from 0.2 kg of fuel still seems impossible, you data must be wrong somewhere. Atomic mass of carbon is 12, oxygen is 16, so CO2 is 44. So, even pure carbon would only produce 3.666(6) times its weight after it’s burned, for any other fuel it should be less.
It com from the air.
If the fuel is just fossil fuel it will only contain carbon and hydrogen. To create carbon dioxide you need oxygen to wait is from the air.
If alcohol is mixed in there is some oxygen but let’s assume there is no alcohol.
So the oxygen in the carbon dioxide is from the air, not the fuel and the majority of the mass of CO2 is the oxygen
Gasoline is made of multiple hydrocarbons with slightly different chemical structures but let’s just look at heptane which is one of the main components of gasoline.
The chemical formula is C7 H16. The mass of carbons is 12 and hydrogen is 1 so the molecular mas is 12*7+1*16 = 100. The mass percentage of carbon is 12*7/100=84%
Carbon dioxide is CO2, the mass of oxygen is 16 so the molecular mass is 12+16*2= 44 of that carbon is 12/44=27% So 73% of the mass is from oxygen that the engine gets from the air
So the fuel is 84% carbon by mass but the CO2 is 27% carbon by mass because
The least doing the calculation for 850g of fuel. It contains 850*0.84= 714 grams of carbon. If you but it with oxygen you ger 714/0.27=2644 grams of CO2
You can also calculate the fule you need for 1 kg of CO2 as 1*.27/.84=0.32 kg
CO2 is not the only exhaust water is also produced. Water is 2/18=11% hydrogen bu mass so from 850gram of fuel we get 850*(1-0.84)/0.11 = 1236 grams of water.
The result is that 1 liter of fuel =0.85kg result in 3.88kg of exhaust which is on average 1-0.85/3.88=78% oxygen from the air by mass.
For gasoline, the ratio of fuel to air is about 1:14.7, so you’re using 14 times as much air as you are gasoline. The “extra” mass comes from the air.
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