This is a PhD-level question that I'm sorry to say is likely to annoy many a high school teacher or university professor trying to get their students to understand the difference between chemical and nuclear reactions. My apologies in advance, but I do think this a useful question from a physics-of-chemistry sort of view, and I'm sure I won't be the only one whose jaw will drop should the assertion prove correct.

I saw an argument years ago describing how nuclear reactions are responsible for the energy lost or gained during the formation and breaking of chemical bonds. Something about gluons or exchange particles being converted to and from energy, and this energy being the resulting reaction enthalpy.

I'll openly admit that it was years ago, and I don't remember the details — hence the question. But just as many physical reactions are actually chemical reactions — the classic example of tearing a piece of paper is actually a breaking of the covalent bonds holding the cellulose chains together — it would be intriguing if all chemical reactions were nuclear reactions.

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    $\begingroup$ This is a PhD-level question. No, it isn’t. After a decent high-school physics course, and certainly after an undergraduate one, one should know that the answer is that nuclei do not change during chemical reactions. $\endgroup$
    – G. Smith
    Mar 2 '20 at 6:11

To a good approximation, the energy changes in a chemical reaction only occur via the rearrangement of the positions of electrons around the atomic nuclei involved. The changes in energy in chemical reactions are too small to cause any transitions in the nuclei of the atoms involved.

Now, are the nucleons completely unaffected by chemical reactions? Since quarks have an electric charge, they will feel the changes in the electromagnetic field due to the rearrangement of electrons during the chemical reaction. However, because of their much larger mass compared to the electron, their closer proximity to other quarks in the nucleus, and their interaction with the strong nuclear force, the chemical reaction will have a negligible affect on them.

As an illustration, imagine a bowling ball and a ping pong ball that are attached to each other with a compressed spring. If the spring is released, the two balls will be propelled away from each other. Even though the spring puts an equal force of both balls, the ping pong ball will receive the vast majority of the energy of the spring because of its lighter mass. In the same way, the energy changes of a chemical reaction will for the most part only affect the electrons of an atom because of their low mass.

As for the tearing of paper, this is also a sort of chemical reaction because it is the electrons that bond the paper together. However, this is a weaker type of bond than the ionic and covalent bonds that form molecules. These types of bonds are most likely hydrogen bonds that can also be seen between water molecules and strands of DNA. These changes in weaker bonds do nothing to the hydrocarbon molecules that make up paper; only the bonds between molecules are broken. If I have a glass of water and pour half of it into a second glass, I only have to break bonds between H$_2$O molecules, not between hydrogen and oxygen atoms.


No, certainly not.

A nuclear reaction involves some change in the nuclei of the constituent particles. Such changes might involve the exitation of rotational or vibrational states of a particular nucleus, or nucleons changing species (protons to neutrons or vice-versa via beta decay).

On the other hand, most chemical reactions can be modeled to extremely high precision by treating the relevant nuclei as point particles of a given mass and charge (see e.g. Density Functional Theory), with no consideration given to their internal structure or excited states. The (overwhelmingly) dominant contributors to the dynamics of those processes are the electrons, so one would not refer to such reactions as nuclear ones.


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