How Bomb Calorimeter Works

• Bomb Calorimeter 

A bomb calorimeter is usually used for the accurate determination of the enthalpy of combustion for food, fuel, and other compounds. It consists of a strong cylindrical steel vessel usually lined with enamel to prevent corrosion. A known mass of the test substance is placed in a platinum crucible inside the bomb. The lid is screwed on tightly and oxygen is provided in through a valve until pressure inside is about 20 atm. After closing the screw valve, the bomb calorimeter is then immersed in a known mass of water in a well-insulated calorimeter. Then, it is allowed to attain a steady temperature. The initial temperature is measured, by using the thermometer present in the calorimeter. The test substance is then, ignited, electrically by passing current through the ignition coil. The temperature of water, which is stirred continuously, is recorded at 30 sec intervals.

From the increase of temperature, heat capacity of bomb calorimeter, we can calculate the enthalpy of combustion.The heat capacity(c), of a body or a system, is defined as the quantity of heat required to change its temperature by 1 kelvin.

• Glass Calorimeter

For most purposes, an ordinary glass calorimeter can be used to determine the value of the change in enthalpy. This usual type of calorimeter is basically an insulated container with thermometer and stirrer. Reactants in stoichiometric amounts are placed in the calorimeter. When the reaction proceeds, the heat energy evolved or absorbed will either cool or warm the system. The temperature of the system is recorded before and after the chemical reaction. Knowing the temperature change, the mass of reactants present and specific heat of water, we can calculate the quantity of heat evolved or absorbed during the reaction.