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 0.3340 g sample of pyrene (C16H10) is burned completely in a bomb calorimeter. The calorimeter is surrounded by 1.130×103 g of water. During the combustion the temperature increases from 25.46 to 27.92 °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 779.8 J/°C. Assuming that no energy is lost to the surroundings, calculate the molar heat of combustion of pyrene based on these data. C16H10(s) + (37/2) O2(g) 5 H2O(l) + 16 CO2(g) + Energy Molar Heat of Combustion =______ kJ/mol

Explanation / Answer

mass of water = 1.130 x 10^3 g

Cp of water = 4.184 g-1°C-1

dT = 27.92 - 25.46 = 2.46 C

Q water = m Cp dT

              = 1.130 x 10^3 x 4.184 x 2.46

              = 11630.6 J

Q bomb = Cp dT

             = 779.8 x 2.46

             = 1918.3 J

Q calorimeter = Q water + Q bomb

                      = 11630.6 + 1918.3

                      = 13548.9 J

                      = 13.548 kJ

C16H10 mass = 0.3340 g

molar mass of C16H10 = 202.25 g/mol

moles of C16H10 = 0.3340 / 202.25

                             = 0.00165

0.00165 mol ------------------- 13.548 kJ heat

1 mol             ----------------------- ??

heat = 8210.9 kJ/mol

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