Sample Activity 2
(Part III: Global Warming and Stoichiometry)
Environmentalists and Chemists Unite !!!
Aisha is a very socially conscious young lady. She is the president of her school's environmental club and is very active in her community. She knows that you are taking a chemistry class and needs your help.
Aisha just got her driver's license but wants to make sure that her driving is carbon neutral. In order to do this, she plans to plant trees that can consume the same amount of carbon dioxide that her car produces. She has heard a statistic that a maple tree consumes 2.52 lbs of carbon dioxide per year [35]. . .and this is where her expertise ends.
You are anxious to take on the challenge, but you need a bit more data, so you email your chemistry teacher. You receive the following response.
Dear Jamal,
It is wonderful to hear that you are not only helping a friend, but have also decided to take on such a worthwhile chemistry problem. Well, I would love to tell you that there is a straightforward answer to your question, but gasoline is a very complex mixture and its combustion increases the complexity even more. However, we can give your friend a general idea by assuming that her gasoline is 87% octane C 8H 1 8 and 13% heptane C 7H 1 6 by volume and the combustion goes to completion. You will also need to make some assumptions with respect to how many miles she will drive each year and the fuel efficiency of her car. I have also attached a data table that you may find useful.
Density heptane 684 g/L
Density octane 692 g/L
3.785 L = 1 gallon
2.2 lbs = 1 kg
With these data in hand, you are ready to start solving your problem. Aisha realizes that these would be useful to communicate more broadly, so she asks you to communicate your work, assumptions, and findings in the form of a brochure that she can display in her environmental awareness office. The front of the brochure should be catchy, attractive, and communicate your message related to global warming and major findings, while the back of your brochure should lay out the details of your assumptions and work.
Sample Solution for Sample Activity 2: Environmentalists and Chemists Unite
Assumptions:
Driver travels 12,000 miles per year
Car gets 24 miles per gallon of gasoline
12,000 miles /year x (1 gallon/ 24 miles) = 500 gallons/ years
Volume of Octane = 87% x 500 gallons/yr = 435 gallons octane/yr = 114.9 L octane/yr
Volume of Heptane = 13% x 500 gallons/yr = 65 gallons heptane/yr = 17.17 L heptane/yr
Mass of Octane = 114.9 L x 692 g/L = 79,530 g
Mass of Heptane = 17.17 L x 684 g/L = 11,746 g
MW Octane = 114 g/mol
MW Heptane = 100 g/mol
Moles of Octane = 79,530 g / 114 g/mol = 697.6 mol
Moles of Heptane = 11, 746 g/ 100 g/mol = 117.5 mol
Combustion of Heptane: C 7H 1 6 +11 O 2 ® 8 H 2O + 7 CO 2
Combustion of Octane: 2 C 8H 1 8 +25 O 2 ®18 H 2O + 16 CO 2
Moles CO 2 produced as a result of combustion of 117.5 moles C 7H 1 6 = 822 moles CO 2
Moles CO 2 produced as a result of combustion of 697.6 moles C 8H 1 8 = 5581 moles CO 2
Total moles CO 2 produced = 822 mol + 5581 mol = 6403 mol CO 2
MW CO 2 = 44 g/mol
Mass CO 2 = 281,700 g = 281.7 kg = 619.8 lb CO 2/yr
619.8 lb CO 2 produced/yr ¸ 2.5 lb CO 2 per tree consumed/yr = 248 Trees
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