Dear Pier,
I agree with you that the user community has been sometimes (often?) sloppy
in the use of scientific terminology firmly established decades ago by the
physical scientists.
One example is to refer to different "strengths" of an acid when
"concentration" is the correct word. Strength refers to the ionization
equilibrium constant which is of course constant for a given acid.
Expressions for designating isotopic abundances are also abused. A delta
value can "increase or decrease", "become more positive or less positive,
more negative or less negative"  but it cannot be "enriched" or "depleted".
"Isotope depletion" is meaningless unless an isotope is specified and it has
sometimes been misused to mean a lower delta value.
You were doing okay with your definitions until you came to "reduction"
.when  you felt a compulsion to mention oxygen!
"Oxidation"  is an "increase in oxidation state (sometimes called valence
state when referring to the element involved)", corresponding to a "loss of
electrons"."Reduction" is a "decrease in oxidation state" corresponding to a
"gain of electrons" So, if you react metallic Na with chlorine  gas to give
NaCl, the Cl2 is the oxidizing agent (electron acceptor) and Na is the
reducing agent (electron donor).  Na is oxidized: Cl2 is reduced. This is
called a "redox reaction". NO OXYGEN is involved.
Note that "oxidation or reducing agent" refers to the whole compound  and
not just the element which changes valence state.
Combustion is commonly considered  to involve oxidation agents containing
oxygen  but I think that there are some folk who  would consider that
concept to be too restrictive.
Release of O2 is only one of many possibilities which can happen in a
fluorination redox reaction. An   example is the reaction of CH4 with F2 to
produce CH3F (fluoromethane) plus HCl. The term "substitution reaction"  is
used in this case because F-atoms replace H-atoms in the reactant methane
There can be further substitution reactions to give CH2F2, CHF3, and CF4. An
interesting question is how to classify fluorination with a compound such as
XeF6 when  the net result could be no change in the valence of F. One could
probably consider the overall reaction to be two reactions, the first a
decomposition reaction which generates F2 followed by a redox fluorination
reaction to generate the appropriate fluoride.
I agree that definitions should be precise, one reason being that sloppy
usage is daunting for a new comer to stable isotope research. Students in my
classes or defending their theses have probably thought  of me as being
unnecessarily picky and many times, I bit my tongue when the attitude was
"You know what I mean"



.
----- Original Message -----
From: "Pier De Groot" <[log in to unmask]>
To: <>
Sent: Wednesday, October 10, 2001 1:33 AM
Subject: definitions of reaction processes?


> Dear all,
>
> While working on my books, I became increasingly confused about some terms
> used for reactions to 'decompose' or 're-arrange' compounds into (gaseous)
> compounds which can be measured on an IRMS for isotopic compositions (e.g.
> H2, CO, CO2, N2, SO2, SF6). These terms are: combustion, pyrolysis and
> reduction.
> Sometimes different terms are used for same processes (eg combustion and
> pyrolysis, or pyrolysis and reduction). And once given a wrong term is
very
> consistent in its wrong use by others further on - a term becomes easily
an
> accepted one, correct or not.
>
> Now I like to get this straight. According to my knowledge the following
> terms, here in relation with reaction/preparation of sample materials for
> stable isotope measurement, are standing for:
>
> Combustion = reaction (oxidation) with O2 or an oxygen donor (eg CuO,
Cu2O,
> V2O5, Cr2O3, NiO, PbO2, Co3O4, WO3, K2Cr2O7, Fe2O3 ..)
>
> Pyrolysis = decomposition of a compound by heat (temperature), without
> addition of an external agent included in the reraction. Catalyzers can be
> included (by definition do not take part of reaction proper).
>
> Reduction = reaction where oxygen from a compound is fixed on an oxygen
> receptor, commonly carbon (eg carbon reduction in a glassy carbon
reactor).
>
> Fluorination = reaction of a compound with fluor (F2) or a fluor agent
> (BrF5, ClF3), generally to release O2 or to form a fluorinated compound,
> such as SF6, CF4, SiF4.... [this last one is less confusing, but goven for
> completeness].
>
> I think it is time we get the right terms for the right processes, and
> someone needs to make a start! If you think I am wrong with my
definitions,
> or think they have to be reshaped, please, let us, listusers, know.
> Since I had discussions before with different stable isotope analysts
about
> this, showing a general confusion on this, I expect quite some reactions
> from you.
>
> I look forward for your reactions,
> Pier.
>
>
****************************************************************************
> ***************
> Dr. Pier A. de Groot
> European Commission
> Joint Research Centre
> Institute for Reference Materials and Measurements (IRMM)
> Retieseweg
> 2440 Geel
> Belgium
> Tel. +32 (0)14 571 628
> Fax +32 (0)14 571 685
> e-mail: [log in to unmask]
>
> Visit my WEB-site about my "Handbook of Stable Isotope Analytical
> Techniques" at:
> http://www.geocities.com/padegroot/index.html
> last update: 27 September, 2001.
>
****************************************************************************
> *********************