Re: Thermoneutral Reactions?

From: Wilco Oelen (photo_at_woelen.nl)
Date: 01/30/05 

Date: 30 Jan 2005 07:32:51 -0800

Farooq,

I would expect that there are no _exact_ thermoneutral reactions. Any
chemical reaction means that matter is reorganized. Of course, one can
imagine that there are two different setups of matter, which are very
close to each other with respect to the energy stored in the system. A
transition from the one setup to the other setup then will only involve
a small net amount of energy. However, such 'almost thermoneutral'
reactions are no more special than any other reaction. They do not
introduce a new concept in physics or chemistry.

I think, that even the exchange of isotopes in certain systems of
labile molecules/complexes cannot be regarded as _exact_ thermoneutral,
although I indeed think that these reactions are close to
thermoneutral. An example of such a reaction is the reaction of the
[CuCl4](2-) complex with 35Cl ions exchanged with 37Cl ions. However,
the mass of the isotopes differs and this might have (albeit very
slight) effects on the potential energy stored in such a complex. The
difference in energy levels is so small, that due to random vibration
(noise) there is no measurable favorite configuration.

Wilco

faroo...@hotmail.com wrote:
> Can somebody give a common example of a thermoneutral chemical
reaction
> (no heat evolved or absorbed)? I thought that every reaction was
either
> endothermic or exothermic but never heard of a thermoneutral reaction
> until browsing a book on chemical kinetics where they just mentioned
in
> a single line about these reactions. Many other kinetics texts such
as
> Laidler, Logan do not mention this term at all. Just thinking can
> isotope-exchange reactions can they be classified as thermoneutral
> reactions?

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