Compared with chemical reactions, the energy changes in nuclear reactions are larger by a factor of roughly:

1. In ordinary chemistry mass changes are far too small to measure. 2. In nuclear reactions the energy changes are much larger, by factors of a million or so. 3. At that scale the mass changes become measurable. 4. Matter to energy conversions are therefore significant in nuclear reactions but not chemical ones. 5. This is why chemistry treats mass as conserved. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 5 'Thermochemistry', sections 5.1-5.3_