Calorimetry

Calorimetry is the experimental measurement of heat exchanged in physical and chemical processes. Its classic technique, the method of mixtures, drops a hot object of known mass into a measured quantity of cool water inside an insulated vessel (a calorimeter) and reads the equilibrium temperature. Conservation of energy — heat lost by the hot body equals heat gained by the water — then yields the unknown, usually the specific heat of the object.

Because an ideal calorimeter exchanges no heat with its surroundings, the balance m_s c_s (T_s − T_eq) = m_w c_w (T_eq − T_w) holds, with every quantity measurable except the one being sought. Real calorimeters correct for the small heat capacity of the vessel itself and for residual losses.

Calorimetry was the workhorse that turned heat from a quality into a quantity, producing the first tables of specific and latent heats. Modern variants — bomb calorimeters, differential scanning calorimetry — measure combustion energies, reaction enthalpies, and the heat signatures of phase transitions.

Developed by Joseph Black and Antoine Lavoisier in the eighteenth century (Lavoisier and Laplace built an ice calorimeter c. 1782) and refined into a precision technique through the nineteenth and twentieth centuries.