The device used to measure heat transfer in chemical reactions is a calorimeter.
A calorimeter measures heat released or absorbed during a chemical reaction or physical change, often by tracking the temperature change of a known mass of water or another substance. A simple coffee-cup calorimeter uses insulated nested cups, a thermometer, and a stirrer. The measured temperature change, together with the material’s heat capacity, allows scientists to calculate energy transfer.
The instrument’s history reaches back to Joseph Black’s 1761 work on latent heat. Antoine Lavoisier and Pierre-Simon Laplace used an ice calorimeter in the winter of 1782–83; heat from a reaction melted surrounding ice. Lavoisier introduced the name “calorimeter” in the eighteenth century.
A thermometer is only one component of many calorimeters: it measures temperature, not heat directly. A barometer measures pressure, while a manometer measures pressure differences. Modern versions include bomb calorimeters, differential scanning calorimeters, and isothermal titration calorimeters.