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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. Find ΔErxn for the combustion of naphthalene given that the heat capacity of the calorimeter is 5.90 kJ/°C.
A
-31.98 kJ
B
-28.92 kJ
C
-36.44 kJ
D
-25.56 kJ
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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 (5.90 kJ/°C).
Calculate the change in temperature (ΔT) by subtracting the initial temperature from the final temperature: ΔT = 31.56 °C - 25.10 °C.
Use the formula for heat absorbed or released by the calorimeter: q = C_calorimeter × ΔT, where C_calorimeter is the heat capacity of the calorimeter.
Since the reaction occurs in a bomb calorimeter, the heat absorbed by the calorimeter (q) is equal to the change in internal energy of the reaction (ΔE_rxn), but with the opposite sign: ΔE_rxn = -q.
Substitute the values into the equation to find ΔE_rxn: ΔE_rxn = -(5.90 kJ/°C × ΔT).