Enthalpy

Enthalpy – a measured variable in thermal analysis

What is 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.

The difference between endothermic and exothermic release:

Endothermic:

  • 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
  • Evaporating liquids
  • Melting solids



Exothermic:

  • 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
Enthalpie 3D Druck Material