Why are the observed energy changes for nuclear processes so much larger than the energy changes for chemical and physical processes?

Nuclear processes involve the nucleus of the atom, which contains protons and neutrons. Some common examples are nuclear fission and fusion, which release large amounts of energy. Chemical processes, on the other hand, involve the electrons in the atom and the interactions between them. Examples of chemical processes are combustion, oxidation, and reduction reactions. Physical processes generally deal with the rearrangement of atoms or molecules without any change in their chemical structure (e.g., phase changes like melting and evaporation).

In nuclear processes, the primary force at play is the strong nuclear force, which acts between protons and neutrons in the nucleus, binding them together. This force is much stronger than the electrostatic force which acts between charged particles (protons and electrons) in chemical processes. A nuclear process involves overcoming the strong nuclear force to break or rearrange the nucleus, thus releasing a significant amount of energy. On the other hand, a chemical process involves overcoming the comparatively weaker electrostatic force to rearrange electrons in atoms and molecules.

The binding energy of nucleons (protons and neutrons) in the nucleus is much higher than the binding energy between electrons and the nucleus in an atom or between atoms in molecules. This binding energy is a measure of the energy required to separate the constituents of a system and is related to the stability of that system. In nuclear processes, the changes in the binding energy are much larger than those in chemical processes. As a result, the energy released (or absorbed) during a nuclear process is considerably larger than that of a chemical or physical process. For example, the energy released during the nuclear fission of one uranium-235 nucleus is about 200 million electron volts (MeV), while the energy change in a typical chemical reaction, such as the combustion of gasoline, is on the order of a few electron volts (eV).

The energy released during a nuclear process can also be attributed to the mass defect, which is the difference between the mass of the nucleus before and after a nuclear reaction. This mass defect is converted into energy according to Einstein's famous equation, \(E=mc^2\), where \(E\) is the energy, \(m\) is the mass defect, and \(c\) is the speed of light. Since the mass defect in a nuclear process is much larger than that in a chemical or physical process, the energy released is orders of magnitude greater. This further underscores the difference in energy scales between nuclear, chemical, and physical processes.