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Practice_Exam5_solutions

# Practice_Exam5_solutions - ECH 3023 Practice Exam 5 Fall...

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ECH 3023 Practice Exam 5 Fall 2006 Open book and 1 page of notes. Show work for full credit. NAME:_________________________ 1. (40 pts) (a) (20) Calculate the HHV and LHV (kJ/g) of mixture consisting of 70 wt% acetone (C 3 H 6 O) and 30 wt% water. (b) (20) Calculate the adiabatic flame temperature T ad when the mixture (25oC) combusted with 100% excess air entering at 25 o C, 1 atm. Assume constant heat capacities, C p , for the gases below, if needed: H 2 O (g): 39 J/mol-K N 2 : 33 J/mol-K O 2 : 33 J/mol-K CO 2 : 49 J/mol-K CO: 31 J/mol-K C 3 H 6 O (g): 100 J/mol-K (a) Basis 1 g fuel C 3 H 6 O (l) + 4 O 2 (g) 3 CO 2 (g) + 3 H 2 O (l) 7 . 1785 ˆ 0 ) ( , - = l Ac c H kJ/mol HHV = (0.7 g)(1 mol/58.08 g)(1785.7) = 21.5 kJ/g LHV = 21.5 kJ/g - (0.7 g)(1 mol/58.08 g)(3*44.01 kJ/mol) = 19.9 kJ/g (b) (n O2 ) theor = (0.7 g)(1 mol/58.08 g)(4 mol O 2 ) = 0.048 mol O 2 n 02,in = 0.096 mol O 2 n N2,in = n N2,out = (0.096)(.79/.21) = 0.363 mol N 2 n 02,out = 0.048 mol O 2 n H2O,out = 0.036 mol + (.3 g)/(18 g/mol) = 0.053 mol H 2 O(g) n CO2,out = 0.036 mol CO 2 (g) [ ] O H p CO p N p O p l O H C c O H p CO p N p O p l H C c C C C C H T T C T C T C T C H H 2 , 2 , 2 , 2 , 0 ) ( 6 3 , 2 , 2 , 2 , 2 , 0 ) ( 60 2 , ) 053 . 0 ( ) 036 . 0 ( ) 363 . 0 ( ) 048 . 0 ( ) 01 . 44 )( 053 . 0 ( ˆ ) 012 . 0 ( ) 01 . 44 )( 053 . 0 ( ) 036 . 0 ( ) 363 . 0 ( ) 048 . 0 ( ˆ ) 012 . 0 ( 0 + + + + - = + + + + + = =

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