Q.State the principle of calorimetry. Explain why a calorimetry experiment is always carried out inside an insulated vessel (a calorimeter) whose own heat capacity is either negligible or is accounted for separately.

The principle of calorimetry states that, when bodies at different temperatures are placed in thermal contact within an isolated system, the quantity of heat lost by the body (or bodies) that cool down is exactly equal to the quantity of heat gained by the body (or bodies) that warm up, as the system settles to one common final temperature -- a direct consequence of the conservation of energy applied to the system as a whole.

This balance is only exactly true if no heat is exchanged with anything outside the system being studied. If the mixing were done in an open, uninsulated container, some heat would leak away to (or, less commonly, be gained from) the surrounding room during the experiment, so the heat actually lost by the hot substance would be more than the heat gained by the cold substance (the missing heat having escaped to the room) -- breaking the simple heat-lost-equals-heat-gained equation and making any specific-heat calculation based on it unreliable. A calorimeter's insulating jacket exists specifically to make the loss of heat to the sur …

State the heat-lost-equals-heat-gained balance as a consequence of energy conservation, then explain that insulation is what makes the sy …

• Treating the calorimeter's insulation as being about keeping the temperature constant, rather than about preventing heat from leaving/entering the system. …