p44_047 - 00 × 10 6 J kg(c If the Sun were composed of the...

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47. (a) The mass of a carbon atom is (12 . 0 u)(1 . 661 × 10 27 kg / u) = 1 . 99 × 10 26 kg, so the number of carbon atoms in 1 . 00 kg of carbon is (1 . 00 kg) / (1 . 99 × 10 26 kg) = 5 . 02 × 10 25 . The heat of combustion per atom is (3 . 3 × 10 7 J / kg) / (5 . 02 × 10 25 atom / kg) = 6 . 58 × 10 19 J / atom. This is 4 . 11 eV / atom. (b) In each combustion event, two oxygen atoms combine with one carbon atom, so the total mass involved is 2(16 . 0u)+(12 . 0 u) = 44 u. This is (44 u)(1 . 661 × 10 27 kg / u) = 7 . 31 × 10 26 kg. Each combustion event produces 6 . 58 × 10 19 J so the energy produced per unit mass of reactants is (6 . 58 × 10 19 J) / (7 . 31 × 10 26 kg) = 9
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Unformatted text preview: . 00 × 10 6 J / kg. (c) If the Sun were composed of the appropriate mixture of carbon and oxygen, the number of combus-tion events that could occur before the Sun burns out would be (2 . × 10 30 kg) / (7 . 31 × 10 − 26 kg) = 2 . 74 × 10 55 . The total energy released would be E = (2 . 74 × 10 55 )(6 . 58 × 10 − 19 J) = 1 . 80 × 10 37 J. If P is the power output of the Sun, the burn time would be t = E P = 1 . 80 × 10 37 J 3 . 9 × 10 26 W = 4 . 62 × 10 10 s = 1460 y ....
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This note was uploaded on 11/12/2011 for the course PHYS 2001 taught by Professor Sprunger during the Fall '08 term at LSU.

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