In an experiment to determine the energy content of a food, a 5.0 g sample of fo

Question

In an experiment to determine the energy content of a food, a 5.0 g sample of food was burned in the oxygen atmosphere of an adiabatic bomb calorimeter. As a result of the combustion reaction, the temperature inside the calorimeter rose by 2.32oC. The heat capacity of the calorimeter had been previously calibrated by passing a current of 1.45 A for 200.0 s under a voltage of 10.0 V. During this electrical heating of the calorimeter, the temperature inside the calorimeter rose by 3.35oC. During both the calibration and the experiment, the calorimeter contained 50.0 g of water in the tank surrounding the bomb. Using the calibration data, calculate the heat capacity, CCAL, of the calorimeter (without the water). calculate the specific energy content of the food (in J/g) as measured by the energy released through the combustion process

Explanation / Answer

m = 5g of food

Q = 0 adiabatic

dT = 2.32

Cp:

I = 1.45 A t = 200 s and V = 10 dT = 3.35ºC

m = 50 g of water in calorimeter surrounding

a) Cp of Food

First, find Cp of calorimeter

Q = CpdT

P = VI = 1.45*10 = 14.5 J/s

t = 200 s

Q = P*t = IV*t = 1.45*10*200 = 2900 J

From Q = mpdT solve for Cp

Cp = Q/(dT) = 2900/(3.35) = 865 J/C change to Ccal

1 kcal = 4184J

Therefore Cp = 0.2067 kcal/c

Calculate Heat Exchange

Qwin = -Qlost

Qwin = calorimeter

Qlost = food burned

Qwin = CpdT = 865 J/C * 2.32C = 2267.8 J

Qlost = m*C

2267 = 5*C

C = 2267/5 = 453.4 J/C

C = 453.4 J/C

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