A 0.373-g sample of naphthalene (C10H8) is burned in a bomb calorimeter and the temperature increases from 24.90 °C to 27.80 °C. The calorimeter contains 1.05E3 g of water and the bomb has a heat capacity of 836 J/°C. Based on this experiment, calculate ΔE for the combustion reaction per mole of naphthalene burned (kJ/mol).
(s) + 12 O2 (g) ---> 10 CO2 (g) + 4
H2O (g) + heat
From the data, the number of moles of Naphthalene used is:
Molar mass of
C10H8 = 128.2g/mol
Moles of C10H8 = 0.373 g / 128.2 g/mol = 2.90 * 10-3mol
The change in temperature is:
27.80 °C - 24.90 °C = 2.9 °C
If only the calorimeter changed temperature (no outside loss or water jacket), then the change in heat energy is: (1KJ = 1000J)
ΔE = 2.9 °C * 836 J/°C = 2424.4 J/°C = 2.42 KJ
To get the ΔErxn (per mole) for the combustion, divide the ΔE above by the moles of C10H8 used.
As heat of combustion is negative,Therefore
ΔErxn (per mole) for the combustion = - (2.42 KJ ) / (2.90 * 10-3mol) = -8.36*10-4 KJ/mol
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