Question

A bomb calorimeter was calibrated by burning 1.031 g of benzoic acid (C6H5COOH, M = 122.13g/mol) in excess oxygen. The temperature inside the calorimeter rose from 23.2°C to 36.7°C.

a. What is the heat capacity of the bomb calorimeter, in units of kJ/°C? ΔrU = -3230 kJ/(1 mol benzoic acid)

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.

c. A sample of nitromethane was burned in the bomb calorimeter calibrated above. The following energy value was determined for the balanced reaction:

4CH3NO2(l) + 3 O2(g) → 4 CO2(g) + 6 H2O(l) + 2 N2(g) ΔrU= -3740 kJ/mol

Calculate ΔHf for nitromethane, in units of kJ/mol.

• Assume that ΔrH= ΔrU within the accuracy of this experiment.

•ΔfH°(gaseous CO2) = - 393.52 kJ/mol ΔfH°(liquid H2O) = - 285.83 kJ/mol.

d. It is assumed above that ΔrH= ΔrU for the combustion of nitromethane.

• Estimate how much work is done, in units of kJ/mol, for the combustion reaction as written in part c at 298 K.

•Is work done by the system, the surroundings, or neither?

•Justify whether the assumption is a valid one.