Calorimters are used to measure the amount of heat released or absorbed by a process. The process could be a reaction, a the cooling of a solid, the melting of ice... any process that involves a transfer of heat. The process releases heat to the calorimter. The heat causes a change in temperature in the calorimeter. Since the change in temperature can be measured, the heat released by the reaction can be determined.   Oops, the QT Movie is 500 pixels tall. It does not fit in a 800x600 pixel screen! Sorry, I'll fix it later...much later.