8/11/2019 How Much Carbon Dioxide is Produced by Driving a Car on One Tank of Petrol

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How much carbon dioxide is produced by driving a car on

one tank of petrol?

Petrol is a mixture of several different organic carbon compounds. The most

common molecules in petrol are the alkanes, consisting of straight or branchedcarbon chains with between 5-8 carbon atoms saturated with hydrogen

molecules (pentane, hexane, heptane and octane).

This is the chemical formula for the complete combustion of octane:

2 C8H18+ 25 O2= 18 H2O + 16 CO2

As you can see from this simple equation,for every single octane molecule that is burned, 8

molecules of CO2 are produced.The standard unit measure of compounds is the mole. 1 mole ofoctane weighs 114 grams and contains avogadros number of molecules, 6.023 x 1023

. 1 mole ofCO2gas weighs 44 grams, but takes up much more volume. Its important to remember from the

ideal gas law that at standard laboratory conditions (25C and 1 atmosphere pressure) one mole

of gas at occupies 24.5 litres. One litre of petrol contains ~737.22 grams of liquid (or ~6.47moles). Therefore, when one litre of petrol is burned, 2.28kg of CO2 are produced,

equivalent to 1268 litres of of CO2gas!! Every single 50 litre tank full of petrol will produce

over 63,400 litres of CO2 gas (63.4 m3), or a volume equivalent to an imaginary cube with sides

4 metres long.

I find it interesting that people talk in terms of kilograms of CO2because it really underestimates

the quantity of gas were dealing with. Gases weigh hardly anything!In fact, 1kg of CO2equals557 litres! Why dont we learn toquote the data figures of CO2in litres instead? How much

petrol must be burned to get 1kg of CO2gas? The answer is that only 324 grams of petrol will

yield 1 kg of CO2.

However, this is the chemical equation for a complete combustion reaction of octane, meaningthat it assumes there is an abundance of oxygen in the atmosphere and that no other

byproducts such as carbon monoxide are produced. Its a simple equation, butreal life is more

complicated, so below is a more advanced chemical equation taking into account the nitrogen in

the atmosphere. 2

2 C8H18+ 25(O2+ 3.76N2)= 18 H2O + 16 CO2+94N2

Taking this further, when an internal combustion engine is running rich, we get incomplete

combustion in which carbon monoxide (CO) and molecular hydrogen (H2) are byproducts of the

reaction, along with other gases of nitrogen. Here is the unbalanced equation occuring at hightemperature:

C8H18+ O2+ N2 = H2O + CO2+ N2 + O2+ CO + H2+ H + O + OH + NO+ N

http://tenerife-training.net/Tenerife-News-Cycling-Blog/wp-content/uploads/2008/03/octane-molecule-3d-model-petrol.pnghttp://tenerife-training.net/Tenerife-News-Cycling-Blog/wp-content/uploads/2008/03/greenhouse-effect.gifhttp://tenerife-training.net/Tenerife-News-Cycling-Blog/wp-content/uploads/2008/03/octane-molecule-3d-model-petrol.pnghttp://tenerife-training.net/Tenerife-News-Cycling-Blog/wp-content/uploads/2008/03/greenhouse-effect.gif

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A advanced link to combustion theory can be readhere.Things get substantially more

complicated when the flame kinetics & high temperatures of an exothermic reaction are taken

into account, as the products are able to break down & react with eachother.Thisis an online

application for determining the products of reaction of popular hyrdrocarbon fuels at elevatedtemperatures and pressures. Other compounds such as SO2are also produced from the

oxidisation of sulphur impurities in petrol.

http://me.queensu.ca/courses/MECH435/notes/Combustion_Theory.ppthttp://me.queensu.ca/courses/MECH435/notes/Combustion_Theory.ppthttp://me.queensu.ca/courses/MECH435/notes/Combustion_Theory.ppthttp://www.wiley.com/college/mechs/ferguson356174/apps/solver/solver.htmlhttp://www.wiley.com/college/mechs/ferguson356174/apps/solver/solver.htmlhttp://www.wiley.com/college/mechs/ferguson356174/apps/solver/solver.htmlhttp://www.wiley.com/college/mechs/ferguson356174/apps/solver/solver.htmlhttp://me.queensu.ca/courses/MECH435/notes/Combustion_Theory.ppt