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Relativity and Chemical Reaction Mass
Name: Bob W.
Status: educator
Grade: 9-12
Location: MT
Country: N/A
Date: 6/4/2005
Question:
If there is a chemical reaction that releases heat (an
exothermic reaction) converts mass to energy. Does it hold true, that
during a chemical reaction that absorbs energy (endothermic reaction)
will add mass to the reactants?
Replies:
The equivalence of energy and mass expressed by the famous equation E=mc^2
applies to chemical reactions too. However, if you do the calculation, you
see that the mass "defect" is so small compared to a typical energy change
of a chemical reaction as to be negligible of any practical consequence.
Vince Calder
Bob,
Thanks for your question. The energy liberated
by an exothermic reaction is not converted to mass.
Rather, the energy is released to the environment
in the form of heat. All chemical reactions obey
the conservation of mass principle.
Dr. Topper
No. The energy from a chemical reaction is not coming from a conversion
of mass but from a rearrangement of the atoms. The atoms all have those
electrons all around them, repelling all the other electrons in all the
other atoms. Ideally they would want to get far apart. But if they
move too far from one, they bump up against another. So they jostle
around, looking for a minimum, like a bunch of ping pong balls being
blown from below, they settle into a low energy state. Then somebody
does a chemical reaction and things are re-arranged, either to a higher
energy state (but still a place where they can remain, otherwise the
chemical reaction would fall back to its reactants), or lower energy
state. Not much relativity theory in all this.
Steve Ross
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