The weight of carbon dioxide?

Question

I just read that when you burn a litre of petrol (which I believe weighs about 1KG) you get 2.4KG of CO2. Clearly the volume of carbon dioxide will be enormous as its a gas but how can it weigh more than twice as much as the fuel it came from?

Answer 1

because every carbon atom that burns joins 2 oxygen molecules to make co2 and oxygen has a mass too.

Answer 2

The main constituent of petrol is Octane. We will use this as our fuel. The reaction is as follows: -

2C8H18 + 25O2 = 16CO2 + 18H2O
(Octane) + (Oxygen) = (Carbon Dioxide + Water)

To make the calculation understandable:
Substitute the Atomic weights of the elements and show as Grams.

Reactants:
Carbon = 12 x 16 = 192 gm
Hydrogen = 1 x 36 = 36 gm
Oxygen = 16 x 50 = 800 gm

Products:
Carbon = 12 x 16 = 192 gm
Hydrogen = 1 x 36 = 36 gm
Oxygen (in CO2) = 16 x 32 = 512 gm + Oxygen (in water) = 16 x 18 = 288 gm. Total Oxygen = 512 + 288 = 800 gm

The total weight of the fuel is 228 gm.
The total weight of Carbon Dioxide is 704 gm.

The amount of CO2 produced is more than 3 x the fuel

Answer 3

Study the chemical reaction. You are adding weight to the carbon of the petrol in the form of oxygen. This is only offset by the loss of hydrogen. They hydrogen has a lower molecular weight than the oxygen so that the end product of the reaction is heavier.

Answer 4

The petrol is hydrocarbon. If we assume that its average composition is CH2 (which is won't be but it is close enough for our purposes) then each CH2 group will react with oxygen to produce H2O and CO2. The atomic weight of CH2 is ~14 and CO2 is 44 so each kg of petrol will produce more than 2kg (actually nearer 3kg) of CO2. It is because oxygen is 16 times heavier than hydrogen and you are reacting oxygen with your hydrocarbon.

Answer 5

Let us assume that the fuel is predominately octane - that's C8H18

Remember that it is burning in air ie O2

The equation for complete combustion is

C8H18 +12.5 O2 ---> 8CO2 + 9H2O

So for every atom of carbon in the fuel you are adding two atoms of oxygen

Now 1 mole of octane weighs 114g and its density is 0.703 g/L

Therefore 1 L of octane will weigh 703 grams and contain 6.17 moles

As said before, for every atom of carbon in the fuel you are adding two atoms of oxygen

8 carbons require 16 oxygens and therefore 8 molecules of O2

Therefore 6.17 moles of octane means that 49.36 moles of O2 are converted to CO2 (and a whole load more are turned into water) weighing 1579.52 g. Add that to the weight of the carbon atoms present in 6.17 moles of octane (ie 8 x 12 x 6.17 = 592.32 g) and you get 2171.84 g of CO2 created

Now that is based on a single type of molecule, in reality petrol is a mix of molecules which vary from place to place - heptane, octane, nonane etc all in different ratios

Answer 6

if you write C+O2---> CO2 in molecular weight, this means that for 12g of Carbon you obtain 12+2*16 = 44g of CO2

44/12 = 3.66 So you see that for 1 kg carbon burned you obtain more than Ikg CO2. I can not retrieve your value of 2.4 not knowing the density of petrol

Answer 7

the mass of petrol depends on its density and might not necessarily be 1 kg

Answer 8

it's the government massaging the figures again!!!

Answer 9

The same way water ways more than ice........