(©2002, François G. Amar, All rights reserved)

Bomb Calorimetry

Here is a schematic drawing of a bomb calorimeter:

The "Bomb" inside is a steel vessel capable of withstanding the large pressure of gas inside as well as the explosive force of the burning reagents inside.

This is a Constant Volume calorimeter since the reaction occurs within a rigid vessel (the bomb) whose volume cannot change.

The heat capacity of the calorimeter is equal to the sum of the heat capacity of the water + the heat capacity of the dry calorimeter (bomb, stirrer, insulated container, etc):

C_calorimeter = C _H2O + C_{dry parts}

If we know C_calorimeter and measure D T, we can obtain the heat change in the calorimeter.

q_calorimeter = C_calorimeter x D T

• but
  • D E_rxn = q_rxn = - q_calorimeter= - C_calorimeter x D T

     

    Example: if a reaction performed in a bomb calorimeter is exothermic then the

    heat absorbed by the calorimeter assembly, q_calorimeter is positive (temperature of calorimeter rises)

    But this is an exothermic reaction (DE_rxn<0) in which no work is done so q_rxn = - q_calorimeter.