The heat capacity of a bomb calorimeter was determined by burning 6.91 g of methane (energy of combustion = −803 kJ/mol CH4) in the bomb. The temperature changed by 11.1°C. (a) What is the heat capacity of the bomb? kJ/°C (b) A 14.0-g sample of acetaldehyde (CH3CHO) produced a temperature increase of 11.3°C in the same calorimeter. What is the energy of combustion of acetaldehyde (in kJ/mol)?

Answer :

(a) The heat capacity of calorimeter

(b) The energy of combustion of acetaldehyde is, 1109.8 kJ/mol

Explanation :

First we have to calculate the heat produced.

where,

= enthalpy change = -803 kJ/mol

q = heat released = ?

m = mass of = 6.91 g

Molar mass of = 16 g/mol

Now put all the given values in the above formula, we get:

(a) Now we have to calculate the heat capacity of calorimeter.

where,

q = heat produced = 346.896 kJ = 346896 J

c = heat capacity of calorimeter = ?

= change in temperature =

Now put all the given values in the above formula, we get:

(b) Now we have to calculate the moles of acetaldehyde.

Mass of = 14.0 g

Molar mass of = 44 g/mol

Now we have to calculate the heat produced in combustion.

where,

q = heat produced = ?

c = heat capacity of calorimeter =

= change in temperature =

Now put all the given values in the above formula, we get:

Now we have to calculate the energy of combustion of acetaldehyde.

where,

= enthalpy change = ?

q = heat released = 353.125 kJ

n = moles of = 0.3182mole

Now put all the given values in the above formula, we get: