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I know that chemical energy is the potential energy stored in the arrangement of atoms within molecules. Forming new chemical bonds releases energy.

what does potential energy mean? Is it the energy released when new chemical bonds are formed? Or is it the needed energy to break the bonds of the compost?

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    $\begingroup$ Potential energy is the energy of attraction/repulsion between "things", they can be atoms/electrons etc. While Potential energy can be used to calculate Free Energy, which, in your context is the WORK required to form a molecule, Potential energy is not the same as Free energy. I would start here: understand what Free Energy is, for instance the Gibbs Free energy. While Potential energy is always used, it is the context in which it is used that makes it useful. On its own, with no guidance, it is not all that useful. $\endgroup$ – Charlie Crown Mar 25 at 20:32
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    $\begingroup$ To further this, at T=0K the internal energy = electronic + ZPVE. Also, at T=0K, U=H=G, so from the electronic POTENTIAL energy and zero point vibrational energy, you can calculate the INTERNAL energy, ENTHALPY, and Gibbs Free energy. I do not offhand know what "energy" is. $\endgroup$ – Charlie Crown Mar 25 at 20:46
  • $\begingroup$ @CharlieCrown Thanks Charlie, but I am a little bit confused, do you have any sources to suggest that could help me understand better the chemical energy $\endgroup$ – Edoardo Mar 25 at 20:59
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    $\begingroup$ And so we return here. $\endgroup$ – Ed V Mar 25 at 21:08
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    $\begingroup$ Edoardo, I would just Wikipedia Gibbs free energy, and/ or Helmholtz free energy. My feeling is that your requirements are basic enough that Maurice answer will give a strong enough feeling of false security to power you through :) $\endgroup$ – Charlie Crown Mar 25 at 21:32
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There exist many different potential energies. Maybe you would prefer an analogy. For example let's consider an object on a table (a ball, a book or a piece of chalk). It has a potential energy which is not chemical for the moment. It is not visible. It is a hidden energy. It can only be shown if you give the object an opportunity to fall down and to go to a place where the potential energy is lower. During the fall, the potential energy is transformed into kinetics energy (its speed increases). When it touches the ground, the kinetics energy is transformed into heat which is another sort of energy. This gravitational potential energy is equal to mgH, where m is the mass of the falling object, H is the beginning height of the table, and g is a universal constant (9.81 m/s2 on Earth). Before the fall, the object has a sort of hidden energy, which we call gravitational potential energy (or mechanical energy), and this energy could only be expressed if you give the object an opportunity to go to a lower place. The object has a higher gravitational potential energy on the table than on the ground.

It is the same in chemistry. H2 and O2 have a similar hidden energy, which is a chemical potential energy. If you break the bonds H-H and O-O, you need energy to do it. You give energy to the atoms. It is similar to the operation of picking up the object on the ground and put it higher, on the table. If you imagine going back to H2 and O2, you would get the energy you had consumed for breaking the bonds. But now, if you prefer recombining the H and O atoms into H2O molecules, you will get much more energy (much more heat).

The object on the ground is similar to H2 and O2. When you give it some energy, you can lift it up to the table, or better to a state of separated H and O atoms. But now if the table is just at the edge of an abyss, you can get more energy by letting the object fall down the cliff. In this case you obtain H2O and not H2 and O2. The chemical potential has decreased to a very low level if the final state is H2O. The fall has produced much more heat than the recombination H2 + O2.

Chemists often use this analogy between height and chemical potential energy (which is usually called enthalpy). They draw short horizontal lines above one another to simulate different states, as if one line represents the table (H and O atoms), and another one (lower) the level of the ground (H2 and O2). Of course the level of H2O is another horizontal line : much much lower.

Have you followed me ? Is it what you needed to understand the potential energy ?

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