Determination of the enthalpy

Reaction enthalpy refers to the enthalpy change observed in a sample during a chemical reaction. Reactions that release energy in the form of heat are classified as exothermic, while reactions requiring energy input are termed endothermic.

A straightforward illustration of an endothermic process is melt enthalpy, where heat must be supplied to transition a solid crystal structure to a liquid phase with molecules moving freely. Conversely, an example of an exothermic reaction is combustion, where a substance reacts with oxygen, resulting in the release of energy.

Description of enthalpy – endothermic vs exothermic reactions

The difference between endothermic and exothermic release:


  • Energy is consumed (heat is absorbed)
  • energy is consumed or needed for reaction to occur
  • increase of inner enthalphy

Examples of endothermic processes include:

  • Dissolving salts in solvent
  • Cracking alkanes
  • Nucleosynthesis (fusion) of elements heavier than nickel
  • Evaporating liquids
  • Melting solids


  • Energy is released (heat is released)
  • reaction occurs spontaneously or triggered
  • decrease of inner enthalphy

Examples of exothermic processes include:

  • The thermite reaction
  • A neutralization (e.g., mixing an acid and a base to form a salt and water)
  • Most polymerization reactions
  • Combustion
  • Respiration
  • Corrosion of metals (an oxidation reaction)
  • Most crystallization processes

Enthalpy determination with a calorimetry

Enthalpy determination using calorimetry involves Differential Scanning Calorimetry (DSC), where the sample’s temperature is compared with an ideally non-reactive reference in the same sample chamber and atmosphere. Both experience the same temperature environment. If the sample’s temperature deviates from the reference, a reaction is occurring. This method provides a quantitative measure of the heat changes associated with chemical reactions.

Sample holder of a calorimeter (Chip-DSC 10) on the upper side, reference measurement integrated on the underside of the sensor
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