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calorimeter
A calorimeter is an object used for calorimetry, or the process of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal microcalorimeters, titration calorimeters and accelerated rate calorimeters are among the most common types. A simple calorimeter just consists of a thermometer attached to a metal container full of water suspended above a combustion chamber.
To find the enthalpy change per mole of a substance A in a reaction between two substances A and B, the substances are added to a calorimeter and the initial and final temperatures (before the reaction started and after it has finished) are noted. Multiplying the temperature change by the mass and specific heat capacities of the substances gives a value for the energy given off or absorbed during the reaction. Dividing the energy change by how many moles of A were present gives its enthalpy change of reaction. This method is used primarily in academic teaching as it describes the theory of calorimetry. It does not account for the heat loss through the container or the heat capacity of the thermometer and container itself.
==History==
The name calorimeter was made up by Antoine Lavoisier.〔Antoine Laurent Lavoisier, Elements of Chemistry: In a New Systematic Order; Containing All the Modern Discoveries, 1789: "I acknowledge the name of Calorimeter, which I have given it, as derived partly from Greek and partly from Latin, is in some degree open to criticism; but in matters of science, a slight deviation from strict etymology, for the sake of giving distinctness of idea, is excusable; and I could not derive the name entirely from Greek without approaching too near to the names of known instruments employed for other purposes."〕 In 1780, he used a guinea pig in his experiments with this device to measure heat production. The heat from the guinea pig's respiration melted snow surrounding the calorimeter, showing that respiratory gas exchange is a combustion, similar to a candle burning.〔(Buchholz, Andrea C; Schoeller, Dale A. (2004). "Is a Calorie a Calorie?". American Journal of Clinical Nutrition 79 (5): 899S–906S. PMID 15113737. Retrieved 2007-03-12 )〕
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