When a 0.235-g sample of benzoic acid is combusted in a bomb calorimeter, the temperature rises 1.643 ∘c . when a 0.275-g sample of caffeine, c8h10o2n4, is burned, the temperature rises 1.584 ∘c . using the value 26.38 kj/g for the heat of combustion of benzoic acid, calculate the heat of combustion per mole of caffeine at constant volume.

Answer : The heat of combustion per mole of caffeine at constant volume is 76197.18 kJ/mole

Explanation :

First we have to calculate the specific heat calorimeter.

Formula used :

where,

Q = heat of combustion of benzoic acid = 26.38 kJ/g = 26380 J/g

m = mass of benzoic acid = 0.235 g

c = specific heat of calorimeter = ?

= change in temperature =

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

Thus, the specific heat of calorimeter is

Now we have to calculate the heat of combustion of caffeine.

Formula used :

where,

Q = heat of combustion of caffeine = ?

c = specific heat of calorimeter =

= change in temperature =

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

Now we have to calculate the moles of caffeine.

Mass of caffeine = 0.275 g

Molar mass of caffeine = 194.19 g/mole

Now we have to calculate the heat of combustion per mole of caffeine at constant volume.

Therefore, the heat of combustion per mole of caffeine at constant volume is 76197.18 kJ/mole