Determination of the enthalpy
The reaction enthalpy is the enthalpy change of a sample during a chemical reaction. Reactions that release energy in the form of heat are called exothermic. Reactions in which energy must be supplied as endothermic.
Melt enthalpies are a simple example of endothermic processes, since one usually has to give heat work in a system in order to break up its solid crystal structure and convert it into a liquid phase with molecules that move freely relative to one another. An example of an exothermic reaction is a simple combustion process in which a substance reacts with oxygen to release energy.
Enthalpy determination with a calorimeter
If one measures a reaction on a calorimeter, one looks at the sample temperature comparatively with an ideally unreactive reference, which is in the same sample space and thus the same atmosphere. Both experience the same temperature environment. If the temperature of the sample to be measured rises or falls in comparison to the reference, a reaction takes place here.