Question

Mothballs are composed primarily of the hydrocarbon naphthalene (C10H8). When 1.025 g of naphthalene burns in a bomb calorimeter, the temperature rises from 24.25 °C to 32.33 °C. Find ∆Erxn for the combustion of naphthalene. The heat capacity of the calorimeter, determined in a separate experiment, is 5.11 kJ>°C.

Answer 1

Answer:

-5.16 × 10³ kJ/mol

Explanation:

According to the law of conservation of the energy, the sum of the heat released by the combustion and the heat absorbed by the bomb calorimeter is zero.

Qcomb + Qcal = 0

Qcomb = - Qcal   [1]

The heat absorbed by the calorimeter (Qcal) can be calculated using the following expression.

Qcal = Ccal . ΔT

where,

Ccal is the heat capacity of the bomb calorimeter

ΔT is the change in the temperature

From [1],

Qcomb = -Qcal = -(5.11 kJ/°C) × (32.33°C - 24.25°C) = -41.3 kJ

Let's consider the molar mass of naphthalene to be 128.17 g/mol. The change in the internal energy (∆Erxn) for the combustion of naphthalene is:

$\frac{-41.3kJ}{1.025g} .\frac{128.17g}{mol} =-5.16 \times 10^{3} kJ/mol$