Like jet fuel, petrol is a mixture that hydrocarbons, the precise composition the which counts upon the rudely oil indigenous which it to be refined. In addition, most gasoline contains additives favor antioxidants, static inhibitors, corrosion inhibitors, and also more.

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What we purchase at the pump is a mixture of numerous compounds. However, given the boiling points provided to distill gasoline (120 - 400 levels Fahrenheit), we recognize its hydrocarbons have between 6 and 12 carbon atoms. Most people consider octane - C8H18 - one acceptable median value1. Octane has actually a density of 0.703 g/mL or 2,661.14 g/gal.


In a petrol engine, a mixture the gasoline and also air is combusted to journey pistons. The pistons revolve the drive shaft, and also the drive tower turns the wheels. In the burning reaction, gasoline (aka, octane, C8H18) combines v atmospheric oxygen (O2) to produce carbon dioxide (CO2) and also water (H20):

C8H18 + O2 -> CO2 + H20 (1)This is the same burning reaction that occurs in our body to generate energy from food. That course, other facets in the wait such together nitrogen and also carbon dioxide are shed in the engine as well as oxygen. Those other aspects will produce other molecules like nitrates and ozone, yet we"ll ignore them in ours calculations.

Of course, we must balance the equation therefore the same number of elements enter and exit our reaction:

2C8H18 + 25O2 -> 16CO2 + 18H20 (2)We deserve to see for every 2 octane molecules that get in our combustion reaction, 16 carbon dioxide molecules are developed (or, reduce the fraction, one molecule the octane produces eight molecule of carbon dioxide). However, octane molecules and carbon dioxide molecules are not the exact same mass, and mass must be conserved.

To determine how plenty of grams that carbon dioxide space produced, we have to calculate the molecular mass of carbon dioxide, the molecule mass the octane, and also the ratio between the two:

(1 m * 12.011 amu) + (2 m * 15.999 amu) = 44.009 amu (3)(8 m * 12.011 amu) + (18 m * 1.008 amu) = 114.232 amu (4)44.009 amu / 114.232 amu = 0.385 (5)We understand that for every octane molecule that enters our reaction produces eight carbon dioxide molecules (Equation 2), and also we recognize that one carbon dioxide molecule is 38.5% the mass of one octane molecule (Equation 5). Together a result, we have the right to calculate how countless grams the carbon dioxide are produced by one gram that octane (aka, gasoline):

8 * 0.385 = 3.080 g CO2 / g C8H18 (6)Given the thickness of octane (0.703 g/mL or 2,661.144 g/gal), we have the right to calculate the pounds that carbon dioxide produced by one gallon the octane (aka, gasoline):

2,661.144 g C8H18/gal * 3.080 g CO2/g C8H18 * 1 lb/453.592 g = 18.07 lbs CO2/gal (7)


There you have actually it! to the best of ours ability, top top average, one gallon of gasoline produces 18.07 pounds of carbon dioxide. If your car gets 20 miles-per-gallon and also you journey 10,000 mile in a year, you"ll develop 4.5 quick tons of carbon dioxide.
Heads up! In 2012, the US energy Information management estimated one gallon of gas to produce 19.6 pounds that carbon dioxide. The discrepancy more than likely stems from the truth that they tested actual gasoline through all that additives and other compounds, not just octane. In additition, castle probably taken into consideration the impact of other gases in the air prefer nitrogen, carbon dioxide, etc.

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Don"t forget! there are various other molecules in the reaction. We aren"t saying that you get 18.1 pounds the carbon from 5.7 pounds of carbon (about the weight of a gallon that gas). That would certainly defy physics! We"re saying you obtain 18.1 pounds the carbon dioxide and 8.3 pounds that water from 5.7 pounds of gasoline (1 gallon) and also 20.5 pounds that oxygen.