Question

The following quote appeared in Chemical and Engineering News (September 3, 1990, p. 52): "One tree can assimilate about 6 kg of CO2 per year or enough to offset the pollution produced by driving one car for 26,000 miles." Is this statement correct? Justify your answer quantitatively. Assume gasoline has the formula C9H16 and that its combustion is complete.

Answer 1

Fast balance:

24.1 Miles Per Gallon is the average milleage consumption

that is

26000 miles will require 24.1 Miles Per Gallon

26000 /24.1 = 1078.83 gallons of gas

that is

1078.83 *3.78541 = 4083.81 liters of gasoline

approx density 0.80

D = mass/V

mass = 4083.81*0.80 = 3267.048 kg of gas

from stoichiometry:

C9H16 + 26O2 --> 9CO2 + 8H2O

MW of C9H16 = 124

MW of CO2 = 44

then

124 kg ---> 9*44 = 396 kg

124 kg of gasoline will produce 396 kg of CO2

1 kg of gasoline per 396/124 = 3.19354

we calculated

3267.048 kg of gasoline, therefore, 3267.048*3.19354 = 10433.44 kg of CO2 will be produced

1 tree can retain 6 kg,

you will need

10433.44 /6 = 1738.906 = 1739 trees for this statement to be true (i.e. to absorb those 26000 mile gasoline consumption)

statement is FALSE