# Does the re-arrangement of chemical bonds happens due to electromagnetic interactions?

The question is of some interest because the storage of energy in a recharable battery is not caused by gravitational (potential) nor by kinetic energy.

From this question Why is current the same in a series circuit? it is clear that the release of energy in a circuit is due to energy loss in the form of EM radiation of each involved electron. The answers are stating that the number of the electrons is unchanged and the charge is unchange too of course.

So the question is, does the re-arrangement of chemical bonds happens due to electromagnetic interactions? And is some part of the EM radiation stored inside the bonds and will be released during the flow through Ohm resistances?

• What do you mean by an 'akkumulator'? – Gert Jul 26 '16 at 12:08
• @Gert Sorry, in German we differ between a battery (once de-charged throw it away) and a recharable battery. I have edited it. – HolgerFiedler Jul 26 '16 at 12:14
• Well the nuclear forces and gravity play no significant role, so yes, EM is responsible for everything that's happening... – lemon Jul 26 '16 at 12:30

## 1 Answer

In a rechargeable battery, two types of reversible chemical reactions take place:

1. Oxidation reaction: in which a chemical, referred to as the reducing agent ($Re$) is oxidised by donating electrons:

$$Re \to Re^{z+} + z e^-$$

1. Reduction reaction: in which a chemical, referred to as the oxidising agent ($Ox$) is reduced by receiving electrons:

$$Ox + z e^- \to Ox^{z-}$$

The overall reaction is thus:

$$Re + Ox \to Re^{z+} + Ox^{z-}$$

The reaction is chosen so that the reaction equilibrium constant:

$$\frac{a_{Rez+}{a_{Oxz-}}}{a_{Re}a_{Ox}}=K$$

... is much larger than unity, so that the reaction is thermodynamically favourable, from left to right.

The battery is made of cells (arranged in series or parallel, or a single cell in some cases), each running such a reaction and providing a flow of electrons when the circuit is closed.

This provision of current continues until all the left hand reagents have been converted to right hand reaction products. Then the battery can no longer provide current and the potential across its electrodes is zero.

But remember that the chosen reactions are reversible: by running a current through a depleted battery and in the reverse direction of discharging mode, the reagents are converted back to the original reagents and the battery is as new.

Note that even with non-rechargeable batteries some degree of recharging is in fact possible but they happen to be much harder to recharge than those designed for that purpose.

The chemical energy stored in chemical compounds is due to changes in the Molecular Orbital structures when reagents convert to reaction products. Take a simple combustion reaction (the burning of coal):

$$C(s) + O_2(g) \to CO_2(g)$$

Once initiated, such a reaction proceeds spontaneously because the overall arrangement of Molecular Orbitals is of a lower level of energy for $CO_2(g)$ than for $C(s) + O_2(g)$. Energy is thus released, here mainly as heat.

In the case of a battery, this reaction energy is released as EMF due to the particular reactions chosen and the physical arrangement of the cell(s).

• Gert, nice answer from a chemical point of view. What I try to find out is that electrons in a current beside their amount and their (of course constant) charge are able to induce in every Ohm resistance EM radiation. How this EM energy is stored during the charge of the rechargeable battery. (May be this is now the better formulation of the question). Could you expand your answer? – HolgerFiedler Jul 26 '16 at 13:38
• @HolgerFiedler: Hi Holger, All accessible energy in a galvanic cell is present as energies of Molecular Orbitals (MOs). When reactions take place, chemical bonds are broken and new ones formed. This is the consequence of rearrangement of the bonding MOs. In an exoenergetic reaction the new arrangement (the 'reaction products') is of lower overall energy than the MO arrangement of the initial state (the 'reagents'). So $E_2-E_1<0$ i.e exoenergetic. In a cell this energy release manifests itself as a current of electrons, when the circuit is closed. – Gert Jul 26 '16 at 15:36
• As with any type of energy it can then be transformed into another like heat, radiation or whatnot. But the primary energy source are the MOs, in the case of a battery cell. – Gert Jul 26 '16 at 15:38