A bomb calorimeter is used to determine the amount of energy liberated when a ma

Question

A bomb calorimeter is used to determine the amount of energy liberated when a mass of soy beans is combusted. The bomb calorimeter is calibrated by combusting 7.77 g of methane which leads to a temperature change of 42.8 C. The delta E combustion for this experiment is -802 kJ/mole. After the calibration of the bomb you load 2.95 g of soybeans into the same calibrated caalorimeter and perform your combustion experiment. The temperature increases by 1.20 C. what is the delta E of combustion for the soybeanss in kJ/mo.. Assume the molecular weight of the soybeans is 180.18 g/mol.

Explanation / Answer

Energy liberated by burning the methane=(7.77g/16g/mol)*802kJ/mol

=389.4712kJ=389471.25J

Using specific heat equation:  

Q =m CT

Q = 389471.25, T = 273.15+42.8=316K, m=180.18, so solve for the calorimeter capacity, C (this equals 6.844J/K).

Repeat the process to find the heat change for the second reaction:
T = 273.15+1.20=274.35, C = 6.844J/K, so you can solve for Q (which, then, equals 358.315kJ).

Since of same calibration,number of moles of methane=2.95g/16g/mol=0.1843

delta E=358.315kJ/0.1843

=-1944.16kJ(negative sign is because of the process is combustion)

  

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