Discuss a method for the measurement of heat of combustion at constant volume (q_v or ∆E).

The heat of combustion at constant volume i.e. internal energy change is measured experimentally by Bomb Calorimeter. It is made up of heavy steel (Bomb) which can stand high pressure. It is surrounded by a bigger vessel which contains water and is insulated. A thermometer and a stirrer are suspended in it. The initial temperature of the water is noted. A known weight of the compound is taken in the platinum cup. Oxygen under high pressure is introduced into the bomb. A current is passed through the filament immersed in the compound. Combustion of the compound takes place. The heat energy evolved during the chemical reaction raises the temperature of water which is carefully recorded from the thermometer. By knowing the rise in temperature and heat capacity of calorimeter, the heat of combustion at constant volume can be calculated by using the expression,
             
where    Q = Heat capacity of the calorimeter