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Multiple Choice
Mothballs are composed primarily of the hydrocarbon naphthalene (C10H8). When 0.820 g of naphthalene burns in a bomb calorimeter, the temperature rises from 25.10 °C to 31.56 °C. If the heat capacity of the calorimeter is 5.11 kJ/°C, what is the ΔErxn for the combustion of naphthalene?
A
-31.5 kJ
B
-31.5 kJ/mol
C
-33.0 kJ
D
-33.0 kJ/mol
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검증된 단계별 안내
1
Identify the given values: mass of naphthalene (0.820 g), initial temperature (25.10 °C), final temperature (31.56 °C), and heat capacity of the calorimeter (5.11 kJ/°C).
Calculate the change in temperature (ΔT) using the formula: ΔT = final temperature - initial temperature. Substitute the given values to find ΔT.
Use the formula for heat absorbed or released by the calorimeter: q = C × ΔT, where C is the heat capacity of the calorimeter. Substitute the values for C and ΔT to find q, the heat absorbed by the calorimeter.
Since the heat absorbed by the calorimeter is equal to the heat released by the combustion of naphthalene, ΔErxn = -q. This is because the system loses heat to the surroundings, which is absorbed by the calorimeter.
To express ΔErxn per mole of naphthalene, calculate the moles of naphthalene using its molar mass (C10H8). Then, divide ΔErxn by the number of moles to find ΔErxn per mole.