# Does the relation between energy and mass, proposed by Einstein hold true for all forms of energy? [duplicate]

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I don't have a strong chemistry background, but I recently stumbled upon an answer that concluded that when supplying a reactant(s) with energy E it should be that the difference between the masses of the product(s) and the reactant(s) be given by $${E\over {c}^2}$$ This was strange enough as the difference of masses had to be zero, unless atoms showed a difference in their atomic weights after the reaction, and this also has to be wrong as if it works like this then it has to also work the reverse way, but you don't see any less number of moles/mass when a reaction releases energy.

This led me to do some search about the topic, until I stumbled upon a paper stating that Einstein’s equation is only valid for light energy, it didn't even state electromagnetic energy which makes it look like a naive one.

Not sure if allowed to paste links here.

## marked as duplicate by PM 2Ring, Ben Crowell, Jon Custer, John Rennie, GiorgioPApr 5 at 22:20

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