A 0.468 g sample of pentane, C 5 H 12 , was burned in a bomb calorimeter. The te
ID: 976401 • Letter: A
Question
A 0.468 g sample of pentane, C5H12, was burned in a bomb calorimeter. The temperature of the calorimeter and 1.00 kg of water in it rose from 20.45 °C to 23.65 °C. The heat capacity of the calorimeter by itself is 2.21 kJ/°C and the specific heat capacity of water is 4.184 J/g.°C What is the heat of combustion per mole of pentane?
A 0.468 g sample of pentane, C5H12, was burned in a bomb calorimeter. The temperature of the calorimeter and 1.00 kg of water in it rose from 20.45 °C to 23.65 °C. The heat capacity of the calorimeter by itself is 2.21 kJ/°C and the specific heat capacity of water is 4.184 J/g.°C What is the heat of combustion per mole of pentane?
Explanation / Answer
mol of pentane = mass/MW = 0.468/72.15 = 0.00648 mol of C5H12
dT = 23.65-20.45 = 3.2 °C
C = 2.21 kJ/°C
Cp = 4.184
Qgained = -Qlost
Qgained = Qwater + Qcalorimeter
Qlost = -HRxn/n
Qwater = m*C*(Tf-Ti) = 1000*4.184*(23.65-20.45) = 13388.8 J
Qcalorimeter = C*dT = 2.21*1000*3.2 = 7072 J
Q total = 13388.8 +7072 = 20460.8 J
Qlost = -Qgain = - 20460.8
Qlost = HRxn/n
Qlost = -20460.8/(0.00648 ) = 3157530.8642 J/mol = 3157.53 kJ/mol
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