Question

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. The heat capacity of the calorimeter, determined in a separate experiment, is 5.11kJ/∘C.

Answer 1

Answer:

$\Delta E_{rxn}$ for combustion of naphthalene is -5164 kJ/mol

Explanation:

$\Delta E_{rxn}=C_{calorimeter}\times \Delta T_{calorimeter}$

where, C refers heat capacity and $\Delta T$ refers change in temperature.

Here, $\Delta T_{calorimeter}=(32.33-24.25)^{0}\textrm{C}=8.08^{0}\textrm{C}$

So, $\Delta E_{rxn}=(5.11\frac{kJ}{^{0}\textrm{C}})\times (8.08^{0}\textrm{C})=41.3kJ$

$\Delta E_{rxn}$ is generally expressed in terms of per mole unit of reactant. Also, $\Delta E_{rxn}$ should be negative as it is an exothermic reaction (temperature increases).

Molar mass of naphthalene is 128.17 g/mol

So, 1.025 g of naphthalene = $\frac{1.025}{128.17}moles$ of naphthalene

                                              = 0.007997 moles of naphthalene

$\Delta E_{rxn}=-\frac{41.3kJ}{0.007997mol}=-5164kJ/mol$