Exam+2_Solution-cs

Exam+2_Solution-cs - #1 (15 points) a) (7 pts) A...

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#1 (15 points) a) (7 pts) A temperature of -10 °C is expected over night. How much antifreeze (ethylene glycol, C 2 O 2 H 6 , M = 62 g/mol) do you have to add to 1 L of water to prevent the window wash fluid in your car from freezing ( ∆ܪ ௠,௪௔௧௘௥ ൌ6 ݆݇/݉݋݈ )? ∆ܶ ൌ 10 ܭ ൌ ሺ273 ܭሻ · 8.314 ܬ/ሺ݉݋݈ · ܭሻ 6 ݇ܬ/݉݋݈ ·ݔ x = 0.0907 n W = 55.6 mol ݔ ൌ ݊ ாீ ݊ ாீ ൅݊ ݊ ாீ ݔ·݊ 1െݔ ൌ 5.97 ݉݋݈ ݉ ாீ ൌ ݊ ாீ ·ܯ ாீ ൌ 370 ݃ Antifreeze needed: _____ 370 ________________ g b) (4 pts) From the included P xy diagram, i. Which line is the bubble point curve? 1 or 2 (circle one) ii. If we are designing a flash evaporator at 20 ° C, what would be the benzene compositions in the liquid and the gas at 35 mm Hg? x B = ____ 0.29 _______, y B =____ 0.55 _____ a) (4 pts) Consider a mixture of three condensable chemicals A, B, and C at 50 ° C and 2 atm. Under these conditions all three components are present in the liquid and vapor phase. A and B can be converted into each other, and the system is in equilibrium. Which parameters need to be specified to describe the system unambiguously? Explain your answer in 2 or 3 sentences. From the Gibbs Phase Rule: DOF = c - Π -r + 2 = 3 – 2 -1 + 2 = 2 Both temperature and pressure are specified so no other parameters can be
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#2 (30 pts) Production of biogas in a digester Consider a 30-L digester charged with 3.75 L of cow dung. The reactor produces 5 L of biogas per liter of cow dung at a pressure of 1 atm and a temperature of 27 ° C. On a dry basis, the resulting gas from the digester contains 80% (v/v) of methane and 20% carbon dioxide. The gas is saturated with water, and is subsequently fed to a combustion chamber. If the gas undergoes complete combustion with 7 mols of dry air, identify the composition of the resulting gas. Solution: DOF (Overall system): 4 Unknowns [n 4 , n 5 , n 6 , n 7 ] -3 Atomic Species [C, O, H] -1 Inert Gas (N 2 ) -1 Ideal Gas Law -1 Complete combustion of methane: CH 4 + O 2 CO 2 + 2H 2 O Volume of biogas: V biogas = 3.75 L cow dung ହ ௅ ஻௜௢௚௔௦ ଵ ௅ ௖௢௪ ௗ௨௡௚ = 18.75 L Moles of biogas: n = ௉௏ ோ் = ሺଵ ௔௧௠ሻሺଵ଼.଻ହ ௅ሻ
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This note was uploaded on 02/22/2012 for the course CHBE 2100 taught by Professor Staff during the Summer '08 term at Georgia Tech.

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Exam+2_Solution-cs - #1 (15 points) a) (7 pts) A...

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