Chemistry > EXAM REVIEW > 2017 Midterm v1 (All)

2017 Midterm v1

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PART A: OPEN ANSWER CHEM 1310 MIDTERM VERSION 1 2 HOUR EXAM 1a) A bomb calorimeter was calibrated by burning 1.031 g of benzoic acid (C6H5COOH, M = 122.13 g/mol) in excess oxygen. The temperature in... side the calorimeter rose from 23.2°C to 36.7°C. What is the heat capacity of the bomb calorimeter, in units of kJ/°C? ΔEcombustion = -3230 kJ/(1 mol benzoic acid) (2 marks) Ccal = 2.01 kJ/°C b) Nitromethane, (CH3NO2, M = 61.04 g/mol), commonly known as “nitro”, is the fuel used in racing cars. Write the formation reaction for liquid nitromethane.(1 mark) C(s, graphite) + 3/2 H2(g) + ½ N2(g) + O2(g) → CH3NO2(l) c) A sample of nitromethane was burned in the bomb calorimeter calibrated above. The following energy value was determined for the balanced reaction: 4 CH3NO2(l) + 3 O2(g) → 4 CO2(g) + 6 H2O(l) + 2 N2(g) ΔE = -3740 kJ Calculate ΔH୤ ଴ for nitromethane. Assume that ΔEcombustion = ΔHcombustion within the accuracy of this experiment. (1 mark) ΔH୤ ଴ (gaseous CO2) = -393.52 kJ/mol, ΔH୤ ଴ (liquid H2O) = -285.83 kJ/mol. ΔHf (CH3NO2) = +113 kJ/mol d) It is assumed above that ΔEcombustion = ΔHcombustion for nitromethane. If nitromethane is burned in the open air at constant pressure, is work done by the system, the surroundings, or neither? If work is done, estimate how much, in units of kJ, for the combustion reaction as written above at 298 K. Is the assumption valid? (2 marks) Since moles of product gases is greater than the moles of reactant gases, the reaction leads to an expansion, so work is done by the system. w = -7.43 kJ ΔEcombustion is accurate to the tens place. Accounting for the difference between ΔEcombustion and ΔHcombustion would only affect the last significant figure by 1 [Show More]

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