It is possible to determine the heat released by a combustion reaction using a d

Question

It is possible to determine the heat released by a combustion reaction using a device called a bomb calorimeter. A bomb calorimeter consists of a sealed combustion chamber (called the bomb) surrounded by a jacket of water. The entire assembly is insulated to prevent heat energy from being lost to the surrounding environment. Energy released by the combustion of a sample inside the bomb heats the bomb and the surrounding water. The heat capacity for the "bomb" portion of a certain calorimeter is Cv= 435.5 JI degree C. The bomb is surrounded by 500.0 ml of water. Initially both the bomb and the surrounding water are at a temperature of temperature of 22.50 degree C. 2.45 grams of a given substance are ignited and burned inside the bomb. After combustion the temperature of the bomb and surrounding water is 27.20 degrees C. Calculate the energy change ( Delta E) for the combustion reaction. Express your answer in kJ per gram of sample. [you may assume that the walls of the insulated container do not absorb any heat. In other words, all heat energy is transferred to the "bomb" and the water].

Explanation / Answer

dT = final temperature - intial temperature

dE = qbomb + qwater

     = CvdT[bomb] + mCpdT[water]

     = 435.5 x 4.7 + 502.45 x 4.186 x 4.7

     = 2.05 + 9.89

     = 11.94 kJ total dE

Per gram change dE = 11.94/2.45 = 4.87 kJ/g of substance

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