capacities of some gases Gas C p (J mol – K – ) C v (J mol – K – ) He . . H . .
CO . . . CALORIMETRY A system is said to be isolated if no exchange or transfer of heat occurs between the system and its surroundings.
When different parts of an isolated system are at different temperature, a quantity of heat transfers from the part at higher temperature to the part at lower temperature. The heat lost by the part at higher temperature is equal to the heat gained by the part at lower temperature. Calorimetry means measurement of heat. When a body at higher temperature is brought in contact with another body at lower temperature, the heat lost by the hot body is equal to the heat gained by the colder body, provided no heat is allowed to escape to the surroundings.
A device in which heat measurement can be done is called a calorimeter . It consists of a metallic vessel and stirrer of the same material, like copper or aluminium. The vessel is kept inside a wooden jacket, which contains heat insulating material, like glass wool etc. The outer jacket acts as a heat shield and reduces the heat loss from the inner vessel.
There is an opening in the outer jacket through which a mercury thermometer can be inserted into the calorimeter (Fig. . ). The following example provides a method by which the specific heat capacity of a given solid can be determinated by using the principle, heat gained is equal to the heat lost.
Example . A sphere of . kg aluminium is placed for sufficient time in a vessel containing boiling water, so that the sphere is at ° C. It is then immediately transfered to .
kg copper calorimeter containing . kg water at ° C. The temperature of water rises and attains a steady state at ° C. Calculate the specific heat capacity of aluminium.
Answer In solving this example, we shall