Re: Lost Mass in Chemical Reactions

mmeron_at_cars3.uchicago.edu
Date: 01/31/05 

Date: Mon, 31 Jan 2005 10:25:37 GMT

In article <1107144812.596145.49700@z14g2000cwz.googlegroups.com>, dbohara@mindspring.com writes:
>WTF are "thermal photons". Now, thermal neutrons exist but have
>nothing to do with chemical reactions. Regardless of semantics, total
>mass does not change in a chemical reaction. The source of energy when
>Oxygen and hydrogen combine has nothing to do with changing mass but a
>lot to do with the difference in energy 'tween combined and uncombined
>molecules. No mass change at all. The energy released in the reaction
>was never tied up as mass.
>In nuclear reactions, there is often a change in mass. For example, a
>neutron will spontaneously decay into a proton, a beta, a neutrino (for
>conservation of angular momentum) and a gamma ray. The gamma ray
>represents lost mass.
>Internal conversion decay whereby a nucleus keeps its atomic mass but
>gains atomic number is a similar process in which a neutron turns into
>a proton giving off excess energy from lost mass.
>Chemical reactions, BY DEFINITION, do not result in mass loss
>(conversion of mass into energy).
>
you got this a tad wrong.

First, the source of energy, in any process, is ***never*** a changing
mass. At most, a change of mass may *result* from exchange of energy.

Second, strictly speaking, mass never changes in an interaction. Mass
is defined through the relationship

        m^2*c^4 = sqrt(E^2 - p^2*c^2)

where E is the energy and p is the momentum. Since both energy and
momentum are conserved quantities, mass is conserved as well.

What is possible, though, is a process where part of the energy is
converted from bound form to "transferable form" (i.e. a form which
can be transfered to other entities nearby). Energy transferred to
photons is of this type. In this case, if you just look on what's
left behind, after the energy transfer has been completed, you get
less energy an *less mass* than you started with.

Third, there is absolutely no *qualitative difference* in this respect
between chemical and nuclear processes, same as there is absolutely no
qualitative difference between a gamma photon and an IR photon. The
difference is only a matter of magnitude. In the case of chemical
reactions the extent of relative mass changes are of the order of
10^(-9) - 10^(-10), very difficult to notice unless on looks very
hard. In the nuclear reactions case the changes are of the order of
10^(-2) - 10^(-3), quite easy to notice.

That's all.

Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"

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