Problem Set 5 Key CHEM103A Dr. Keller

Problem Set 5 Key CHEM103A Dr. Keller - CHEMISTRY 103A,...

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CHEMISTRY 103A, Sections 7-10 Problem Set 5 17 Points Answer Key Problem 1 (eight points) A lot of windbaggery is flooding the media these days about alternative fuels, especially ethanol made from corn. This problem deals with calculating the amount of energy (heat) produced when several different fuels undergo combustion. Standard Enthalpies of Formation Substance ∆° H f , kJ/mol CH 4 (g) -74.87 C 8 H 18 (l) -249.95 C 2 H 5 OH(l) -235.10 CO 2 (g) -393.50 H 2 O(l) -285.80 H 2 (g) 0.00 O 2 (g) 0.00 (a) How much energy (heat) in kJ is released when 1.000 kg of octane (C 8 H 18 (l), the principal component of gasoline) undergoes combustion? The molecular weight of octane is 114.23. This means the weight of one mole of octane is 114.23 g. The balanced equation for the combustion is 2 C 8 H 18 + 25 O 2 → 16 CO 2 + 18 H 2 O H = 16(-393.50) + 18(-285.80) -2(-249.95) -25(0) = -10940.50 kJ Note that -10940.50 kJ is for two moles of octane
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8 18 8 18 8 18 8 18 1 _ 10940.50 1000 _ 47,888.03 114.23 _ 2 _ mol C H kJ g C H kJ g C H mol C H - = - 4 4 4 4 1 _ 890.23 1000 _ 55,500.62 16.04 _ 1 _ mol CH kJ g CH kJ g CH mol CH - = - 2 5 2 5 2 5 2 5 1 _ 1409.30 1000 _ 30,590.40 46.07 _ 1 _ mol C H OH kJ g C H OH kJ
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This homework help was uploaded on 04/14/2008 for the course CHEM 103a taught by Professor Weso during the Fall '08 term at University of Arizona- Tucson.

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Problem Set 5 Key CHEM103A Dr. Keller - CHEMISTRY 103A,...

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