Question

The enthalpy of combustion of benzoic acid (C6H5COOH) which is often used to calibrate calorimeters, is −3227 kJ/mol. When 1.09 g of benzoic acid was burned in a calorimeter, the temperature increased by 3.662◦C. What is the overall heat capacity of the calorimeter? The overall heat capacity includes the calorimeter hardware and the water that is in it. Answer in units of kJ/ ◦C.

Answer 1

Answer : The heat capacity of the bomb calorimeter
`7.865kJ/^oC`

Explanation :

First we have to calculate the heat released by the combustion.

`q=n* \Delta H`

where,

q = heat released by combustion = ?

n = moles of benzoic acid =
`\frac{\text{Mass of benzoic acid}}{\text{Molar mass of benzoic acid}}=(1.09g)/(122.122g/mole)=0.00893mole`

`\Delta H` = enthalpy of combustion = 3227 kJ/mole

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

`q=(0.00893mole)* (3227kJ/mole)=28.8kJ`

Now we have to calculate the heat capacity of the bomb calorimeter.

Heat released by the reaction = Heat absorbed by the calorimeter

`q=c* \Delta T`

where,

q = heat released by the reaction = 28.8 kJ = 28800 J

`c` = heat capacity of calorimeter = ?

`\Delta T` = change in temperature =
`3.662^oC`

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

`28800J=(c* 3.662^oC)`

`c=7864.55J/^oC=7.865kJ/^oC`

Therefore, the heat capacity of the bomb calorimeter
`7.865kJ/^oC`