OnlyMe, look over these reversible chemical reactions and tell which side is heavier and wich lighter? Left or right?
Emil, when an electron in a hydrogen atom emits a photon, does it stop being hydrogen? If not then the argument above has no merit, as all you are doing is comparing the atoms involved, not their mass.
Edit: I should add that the mass involved with a single photon emission or even likely a billion (a wild guess) would not be measureable and without changing actual particle balances even chemical reactions have little measureable impact on total mass. Keep in mind many chemical reactions really just involve how a group of atoms share an electron charge. Unless you actually remove an electron in the process of an interaction the total mass at that scale is unaffected.
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