Derived from the Latin word for heat and the Greek for measure, calorimetry is defined as the science of measuring the change in heat associated with a chemical reaction.
A calorimeter is used to measure the change of heat. Noting the internal temperature of a calorimeter before and after the addition of chemicals allows for the accurate reading of the change in heat produced by the reaction. The chemicals themselves constitute the system and the calorimeter is classed as the surroundings. The insulated casing of the calorimeter ensures any change in heat is caused by the reaction in the system and not by any outside influence.