Assume your calorimeter is not perfect. Burning 0.5 lg of ethanol resulted in a

Question

Assume your calorimeter is not perfect. Burning 0.5 lg of ethanol resulted in a 10 degree C rise in the temperature of the 200 mL of water in your calorimeter. Show your work, How much energy was released by burning 0.51 g of ethanol? How much energy is required to raise the temperature of 200 mL of water by 10 degree C? How much energy was lost to the surroundings in this calorimetric experiment? Express this value as a total number of kJ as well as a percentage of the total heat released by burning ethanol. What is the heat capacity of this calorimetric apparatus (C_cal)?

Explanation / Answer

Q. Assume your calorimeter is not perfect. Burning of 0.51g of ethanol resulted in a
10degC rise in the temperature of the 200 ml of water in your calorimeter. Show your

work.
C2H5OH + 7/2O2 = 2CO2 + 3H2O

(a)How much energy was released by burning 0.51g of ethanol?
Molar mass of ethanol C2H5OH, MW = 46 g/mol
Moles of C2H5OH = W/MW = 0.51/46 = 0.011 mol
Enhalpy of combustion, DH = 1368 kJ/mol

Energy released, Qr = n*DH = 0.011*1368 = 15.17 kJ

(b) How much energy is required to raise the temperature of 200ml of water by 10degC?
specific heat of water, cp = 4.184 J/g-degC
change in temperature, DT = 10 degC
density of water = 1g/cm3

mass of water in the calorimeter, m = 200*1 = 200 g
Ql = m*cp*DT=200*4.184*10=8368 J = 8.37kJ

(c) How much energy was lost to the surroundings in this calorimetric experiment?
Energy lost = Qr-Ql=15.17-8.37 = 6.8 kJ

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