Question

When 1.025 g of naphthalene (c10h8) burns 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 is 5.11 kj/°c?

Answer 1

Answer : The $\Delta E$ for the combustion of naphthalene is $5161.25KJ/mole$

Solution : Given,

Mass of naphthalene = 1.025 g

Initial temperature = $24.25^oC$

Final temperature = $32.33^oC$

Specific heat capacity of calorimeter = $5.11KJ/^oC$

Molar mass of naphthalene = 128 g/mole

First, we have to calculate the heat absorbed, $q$

Formula used :

$q=c\times \Delta T=c\times (T_{final}-T_{initial})$

Now put all the given values in this formula, we get

$q=(5.11KJ/^oC)\times (32.33^oCT-24.25^oC)=41.29KJ$

Now we have to calculate the moles of naphthalene.

Moles of $C_{10}H_{8}$ = $\frac{\text{ Mass of }C_{10}H_{8}}{\text{ Molar mass of }C_{10}H_{8}}=\frac{1.025g}{128g/mole}=0.0080moles$

Now we have to calculate the $\Delta E$ for combustion of naphthalene.

$\Delta E=\frac{q}{n}$

where,

q = heat absorbed

n = number of moles

Now put all the values in this formula, we get

$\Delta E=\frac{41.29KJ}{0.0080moles}=5161.25KJ/mole$

Therefore, the $\Delta E$ for the combustion of naphthalene is $5161.25KJ/mole$