Thermochemistry question

Question

Since it can be obtained in very high purity, benzoic acid is one of the classic materials used for determining the heat capacity of bomb calorimeters.

The heat of combustion of benzoic acid, HC₇H₅O₂ is -3227 kJ mol^-1.

When 2.85 g of HC₇H₅O₂ (molar mass = 122.12 g/mol) was burned in a bomb calorimeter, the temperature of the calorimeter changed from 24.05 ºC to 29.19 ºC. What is the heat capacity of the calorimeter in units of kJ/ºC?

Answer 1

We know the heat of combustion is -3227 kJ/mole. So, let us first find out how many moles of benzoic acid we have: 2.85 g x 1 mole/122.12 g = 0.02334 moles benzoic acid

How much heat does this amount of benzoic acid generate when burned?

0.02334 moles x -3227 kJ/mole = 75.31 kJ

What is the change in temperature produced in this experiment?

∆T = 29.19º - 24.05º = 5.14ºC

Now we can determine the heat capacity of the calorimeter:

75.31 kJ/5.14ºC = 14.65 kJ/ºC