Which one of the following statements about the Principle of Calorimetry is correct ?
It is always valid.
It is valid when temperature is constant.
It is valid only when there is no change of state.
It is valid only under equilibrium condition.
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC CISF-AC-EXE – 2018
The Principle of Calorimetry is based on the law of conservation of energy. It states that in an isolated system, the total amount of heat lost by the hot bodies is equal to the total amount of heat gained by the cold bodies. This principle is fundamentally valid whenever heat exchange occurs in an isolated system, including processes involving changes of state (by accounting for latent heat) and processes involving temperature changes. Options B, C, and D state conditions under which the principle is *only* valid, which are incorrect limitations. The principle is valid even when temperature is not constant (during temperature change), when there is a change of state (by including latent heat), and it describes the process of heat exchange *towards* equilibrium, not only at equilibrium. Therefore, “It is always valid” (interpreted as valid in an isolated system for which it is defined) is the most accurate statement among the choices, as the other options describe false limitations.
The Principle of Calorimetry is based on energy conservation in thermal interactions and applies in isolated systems, irrespective of whether temperature changes or phase changes occur.