Mothballs are composed primarily of the hydrocarbon naphthalene (C10H8). When 1.025 g of naphthalene is burned in a bomb calorimeter, the temperature rises from 24.25°C to 32.33°C. Find ΔErxn for the combustion of naphthalene given that the heat capacity of the calorimeter is 5.11 kJ/°C.

• A. -61.0 kJ/mol
• B. -31.8 kJ/mol
• C. -51.2 kJ/mol
• D. -41.5 kJ/mol

Answer: (D)

Verified step by step guidance

1. Start by understanding the problem: We need to find the change in internal energy (ΔErxn) for the combustion of naphthalene using a bomb calorimeter. The heat capacity of the calorimeter and the temperature change are given.
2. Calculate the total heat absorbed by the calorimeter using the formula: Q = C × ΔT, where Q is the heat absorbed, C is the heat capacity of the calorimeter, and ΔT is the change in temperature. Here, ΔT = 32.33°C - 24.25°C.
3. Once you have calculated the heat absorbed (Q), recognize that this heat is equal to the change in internal energy (ΔErxn) for the reaction, but it is expressed in kJ for the amount of naphthalene burned.
4. Convert the heat absorbed (Q) to the change in internal energy per mole of naphthalene. First, find the moles of naphthalene burned using its molar mass (C10H8 has a molar mass of approximately 128.17 g/mol). Use the formula: moles = mass / molar mass.
5. Finally, divide the total heat absorbed (Q) by the moles of naphthalene to find ΔErxn in kJ/mol. This will give you the change in internal energy per mole of naphthalene combusted.