Under what conditions is the heat released or absorbed by a chemical reaction a.
ID: 477646 • Letter: U
Question
Under what conditions is the heat released or absorbed by a chemical reaction a. equal to the ENTHALPY change? b. equal to the INTERNAL ENERGY change? c. neither the exact ENTHALPY nor the exact ENERGY change?
(This problem is exactly what you will do in Lab 1) A 175 gram donut is analyzed in a bomb calorimeter. 1.000 grams of the donut is burned in the calorimeter. The temperature of the calorimeter increases by 2.47 °C. Given that the total heat capacity of the bomb calorimeter is 10.1 kJ/K, a. What is the heat energy content of the donut in kJ/gram? b. What is the total heat energy content of the donut? c. How many food calories are in this donut? When we list food “calories” we really mean kilocalories, where 1 kcal is 4.184 kJ.
Explanation / Answer
Ans : equal to the ENTHALPY change
A. Heat energy content = 10.1 kj/k * (2.47 +273)
= 2782.2 Kj
B. Total heat content Q = mCpdT
= 175/1000*4.184*(273+2.47)
= 201Kj
C.calories in food= 201 Kj
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