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Exam2AKey

# Exam2AKey - 1(15 Starting from the relationship below for S...

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1) (15) Starting from the relationship below for S of the universe, derive the expression that relates the free energy change to H and S of the system. S univ = S surr + S sys need all system quantities G S H S T S H S T H T H T q S sys sys univ sys sys univ sys surr surr = - = - + Τ - = - = = = 2) a) (15) As part of a study of the efficiency of different fuels, 1.00 g of liquid benzene, C 6 H 6 , was burned in a bomb calorimeter whose heat capacity was 2.88 kJ/ o C. The temperature of the calorimeter increased from 24.3 to 38.8 o C. What is the molar energy of combustion for benzene? q sys = -q cal E = -C T = -(2.88 kJ/ o C) (+14.5 o C) = -41.76 kJ (this is for combusting 1.00 g of benzene) 1.00 g x benzene g 78.11 benzene mol 1 = 0.0128 mol benzene molar energy : mol 0.0128 kJ 41.76 - = -3262 kJ/mol b) (15) What is the molar enthalpy of combustion at 25 o C for benzene? C 6 H 6 (l) + 15 / 2 O 2 (g) barb2right 6 CO 2 (g) + 3 H 2 O(l) E = H - n gas RT -3262 kJ = H - (6 – 7.5 mol) (0.00831 kJ/mol-K) (298 K) H = -3262 – 3.71 = -3266 kJ/mol

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3) Use the following thermodynamic data in this question.
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