How are energy inputs and outputs related to chemical reactions

The large number of areas covered by the chemical energetics can be explained by the different forms in which chemical energy can be released: heat and combustion work, electrical energy in electrochemistry, radiant energy in chemiluminescent systems.

The chemical energy provided by a reaction reflects the energy balance associated with the electronic modifications suffered by the species involved.

From an energy point of view, a chemical reaction between molecules can be schematized in two stages. The first requires a supply of energy and corresponds to the rupture of the bonds of the reactant molecules with release of the atoms which constitute them.

The second releases energy and concerns the creation, by recombination of these atoms, of new bonds entering the structure of the reaction molecules.

As a general rule, the energy released in the second stage is greater than the first. We are talking about exothermic reaction. The difference between these two energies (reaction enthalpy) measures the amount of chemical energy transferred to the external environment.

It is conceivable that this quantity translates, not only the number, but also the strength of the connections involved.

In an exothermic reaction, energy is an output. However inn an endothermic reaction, energy is an input.

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