A bomb calorimeter , or constant volume calorimeter, is a device often used to d
ID: 1043237 • Letter: A
Question
A bomb calorimeter, or constant volume calorimeter, is a device often used to determine the heat of combustion of fuels and the energy content of foods.
Since the "bomb" itself can absorb energy, a separate experiment is needed to determine the heat capacity of the calorimeter. This is known as calibrating the calorimeter.
In the laboratory a student burns a 0.451-g sample of biphenyl(C12H10) in a bomb calorimeter containing 1140.g of water. The temperature increases from 24.40 °C to 27.60 °C. The heat capacity of water is 4.184 J g-1°C-1.
The molar heat of combustion is ?6251 kJ per mole of biphenyl.
Calculate the heat capacity of the calorimeter.
heat capacity of calorimeter = J/°C
Explanation / Answer
Q = mc?T
Q = heat energy (Joules, J), m = mass of a substance (kg)
c = specific heat (units J/kg?K), ? is a symbol meaning "the change in"
?T = change in temperature (Kelvins, K)
Mass of water = 1140 gm
?T = 27.6 - 24.4 = 3.2 °C
Let us calculate the heat used to heat water
Q = 1140 x 4.184 x 3.2 = 15263.232
Theoretical value of heat released from biphenyl
Molar mass of C12H10 is 154.2078 g/mol
Energy is converted from Kilo joules to joules
Q = 0.451 x 6251 x 1000 / 154.2078 = 18281.831 Joules
Energy absorbed by Calorimeter = 15263.232 - 18281.831 = 3018.599 Joules
heat capacity of calorimeter = 3018.599 Joules / 3.2 °C = 943.312 J/°C
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