Measurement of and : calorimetry
In calorimetry the process is carried out in a vessel called the calorimeter, which is immersed in a known volume of liquid . knowing the heat capacities of the liquid and that of the calorimeter, it is possible to determine the heat evolved in the process by measuring temperature changes. Measurements are made under 2 different conditions:
(a)at constant volume
(b)at constant pressure
Measurements:
Heat absorbed at constant volume is measured in a bomb calorimeter.
Under these conditions no work is done since the volume of the sealed chamber doesn't change. Thus the temperature change produced in the calorimeter is converted to
measurements:
We know that (at constant ) and, therefore, heat absorbed or evolved, , at constant pressure is also called the heat of reaction or enthalpy of reaction, .
In an exothermic reaction, heat is evolved, system loses heat to the surroundings . therefore, will be negative and also is .similarly the vice versa occurs in an endothermic reaction .

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