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

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 0.402-g sample of naphthalene (C10H8) in a bomb calorimeter containing 1190. g of water The temperature increases from 24.50 degree C to 27.30 degree C. The heat capacity of water is 4.184 J g^-1 degree C^-1. The molar heat of combustion is -5137 kJ per mole of naphthalene. Calculate the beat capacity of the calorimeter

Explanation / Answer

m = 0.402 g of napth

m = 1190 g of water

Ti = 27.30

Tf = 24.50

Cp w = 4.18

Hrxn = -5157 kJ7mol

NOTE:

heat realeased by combustion --> goes to water --> equals the heat absorbed by calorimeter

Qcombustion= Qwater + Qcalorimeter

Calcualte heat of combustion

moles of naph = mass/MW = 0.402/128 = 0.00314 mol of nahp

Q = Hrxn * n = -5157*0.00314 = -16.196 kJ

Qwater

Qw = m*Cp*(Tf-Ti)

Qw = 1190g*4.18J/gC*(27.30-24.50) = 13927 J or 13.93 kJ

Qw = -13.93 kJ

Finally:

Qrxn = Qw + Qcalorimet

-16.196 = -13.93 kJ + Qcalorimeter

Qcalor = 2.266 klJ

Qcalor = C*(Tf-Ti)

C = Q/(Tf-Ti) = 2.266/(27.30-24.5) = 0.809 kJ/C

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