Describe the measurement of `Delta U` by bomb calorimeter.

Explanation

The heat of combustion of a substance at constant volume is measured by calorimetric method. The method is called bomb calorimeter method.

The 'bomb' is a closed container made of heavy steel. It can withstand the high pressure developed inside it. The bomb is coated on the inside with gold to prevent oxidation of steel during the combustion reaction. The bomb is shown in the figure below. A known mass of the substance whose heat of combustion is to be determine is taken in the platinum cup. The bomb is filled with oxygen at a pressure of 20-25 atmospheres. The bomb is closed with a tight screw cap.
The bomb is submerged in a water bath taken in n insulated outer vessel. Stirrer and thermometer are dipped in the water bath. The initial temperature of the water bath is noted. Let it be `t_(1).^(@)C`. The combustion is initiated by passing electric current through the platinum filament. The heat evolved during combusion raises the temperature recorded by the thermometer is noted. Let it be `t_(2).^(@)C`.
Calculation :
Let the mass of the substance taken be 'm' g.
Let the molecular mass of the substance taken be 'M'.
Let the heat capacity of calorimeter be 'Q'
Let `Delta t` be the rise in temperature, `Delta t = t_(2) - t_(1)`
Then, `Delta U` the heat of combustion at constant volume is calculated by the equation
`Delta U = Q xx Delta t (M)/(m)J`