My car's CO2 emission is 163grams per kilometer?

Question

My Car has a CO2 emission rating and is taxed as 163 grammes per km. What I don't understand is, I only use 70ml (approx. 70grammes) of fuel per kilometer. How can I put out 163 grammes when I only put in (incl. water contained in fuel etc) 70 grammes?

Answer 1

its all a con to get more money outta you....   has anyone actually seen the hole in the ozone?   and put their hands into it??   sounds dodgy to me...

Answer 2

This is chemistry. Assume that all petrol is n-octane, it isn't but it's a good approximation. The reaction is:

2C8H18 + 25O2 = 16CO2 +18H2O

Carbon has an atomic weight of 12, Hydrogen is 1 and Oxygen is 16. So n-octane has a molecular weight of 114 and carbon dioxide has a molecular weight of 44. Eight carbons lose 18 from the molecular weight and gain 256 between them. Eight CO2 molecules have a combined molecular weight of 352 against the molecular weight of octane at 114. That is where your extra mass is coming from.

Answer 3

You are missing the oxygen that your car takes in to combust the fuel.  CO2 only gets the C component from the fuel, it gets the 2 O atoms from the air, thus increasing the total mass of emissions.  There is some oxygen in the fuel you use but  its pretty small and only there to reduce other pollutants like NOx and CO