CO2 emissions, a question

[Silver993tt]

My car supposedly puts out 155g/km of carbon per km. The car on average uses 6 litres/100km of fuel. Therefore, every 100km my car outputs 15.5kg of carbon. How is this possible when the fuel used (6 litres) weighs a little under 6 kilos? How can 15.5kg of carbon be produced from 6kg or source material ?

[blank]

Because of the air it uses at the same time - about 15x the mass of fuel it uses (for petrol).

[Basic]

I’d add that what is measured is carbon dioxide per kilometre, not just carbon
Carbon dioxide is 3.7 times heavier than carbon. (Carbon is 12grammes, and oxygen 16. So CO2 is 44g, compared to carbon’s 12.)

So assuming all your petrol is ‘converted’ when burnt, each kg of carbon in the petrol equals 3.7kg of CO2.

As petrol is about 90% carbon, each litre of petrol use equals about 90% of 3.7kg, or 3.3kg.
So if you use 6litres/100km, this equals 6*3.3, or 19.8kg of CO2 every 100km.



Mmm... 15.5kg, you say. Well, obviously my science doesn’t seem to work does it?

I guess some of the petrol is turned into other stuff, rather than being emitted as CO2 from the exhaust.

[Silver993tt]

ok, thanks. The media are always talking about carbon outputs in weight from cars rather than CO2 in weight.

[mcford]

Basic said:

I guess some of the petrol is turned into other stuff, rather than being emitted as CO2 from the exhaust.

The petrol is also turned into carbon monoxide, hydrocarbons and oxides of nitrogen, the catalyst treats these producing more carbon dioxide and water.