The water equivalent of a calorimeter

Even though energy is never lost, when mixing two liquids of different temperatures, you never measure a temperature of mixtures that is exactly between the initial temperatures. This is because some of the heat is absorbed by the reaction vessel. Calorimeters are reaction vessels that are characterised by the fact that they allow very little heat exchange with the reaction mixture inside. Nevertheless, in order to work accurately, the heat capacity of the calorimeter must be determined so that measurements of the heat of reaction that take place in it can be corrected appropriately.