A bomb calorimeter, or a constant volume calorimeter, is a device often used to

Question

A bomb calorimeter, or a constant volume calorimeter, is a device often used to determine the heat of combustion of fuels and the energy content of foods. In an experiment, a 0.6774 g sample of para-benzoquinone (C6H4O2) is burned completely in a bomb calorimeter. The calorimeter is surrounded by 1.043×103 g of water. During the combustion the temperature increases from 28.12 to 31.26 °C. The heat capacity of water is 4.184 J g-1°C-1. The heat capacity of the calorimeter was determined in a previous experiment to be 923.8 J/°C. Assuming that no energy is lost to the surroundings, calculate the molar heat of combustion of para-benzoquinone based on these data. C6H4O2(s) + 6O2(g) 2 H2O(l) + 6 CO2(g) + Energy Molar Heat of Combustion =___________ kJ/mol

Explanation / Answer

mass of water = 1.043×10^3 g

Cp of water = 4.184 J g-1°C-1

dT = (31.26 -28.12) = 3.14 oC

Q water = m Cp dT = 1.043×10^3 x 4.184 x 3.14 = 13702.68 J

Q bomb = Cp dT = 923.8 x 3.14 = 2900.73 J

Q calorimeter = Q water + Q bomb

                       = 13702.8 + 2900.73

                       = 16603.5 J

                        = 16.6 kJ

moles of para-benzoquinone (C6H4O2) = 0.6774 / 108.09

                                                                  = 0.006267

0.006267 mol -----------------------> 16.6 kJ

1 mol -----------------------> 16.6 / 0.006267 = 2648.8 kJ/mol

Molar Heat of Combustion = - 2648.8 kJ/mol

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