Thermodynamics and log–contrast analysis in fluid geochemistry
dc.contributor.author
dc.contributor.editor
dc.date.accessioned
2008-05-06T10:02:56Z
dc.date.available
2008-05-06T10:02:56Z
dc.date.issued
2005-10
dc.identifier.citation
Buccianti, A.; Nisi, B.; Vaselli, O. 'Thermodynamics and log–contrast analysis in fluid geochemistry' a CODAWORK’05. Girona: La Universitat, 2005 [consulta: 6 maig 2008]. Necessita Adobe Acrobat. Disponible a Internet a: http://hdl.handle.net/10256/687
dc.identifier.isbn
84-8458-222-1
dc.identifier.uri
dc.description.abstract
There are two principal chemical concepts that are important for studying the natural
environment. The first one is thermodynamics, which describes whether a system is at
equilibrium or can spontaneously change by chemical reactions. The second main concept
is how fast chemical reactions (kinetics or rate of chemical change) take place whenever
they start. In this work we examine a natural system in which both thermodynamics and
kinetic factors are important in determining the abundance of NH+4 , NO−2 and NO−3 in
superficial waters. Samples were collected in the Arno Basin (Tuscany, Italy), a system in
which natural and antrophic effects both contribute to highly modify the chemical composition
of water. Thermodynamical modelling based on the reduction-oxidation reactions
involving the passage NH+4 -> NO−2 -> NO−3 in equilibrium conditions has allowed to
determine the Eh redox potential values able to characterise the state of each sample and,
consequently, of the fluid environment from which it was drawn. Just as pH expresses
the concentration of H+ in solution, redox potential is used to express the tendency of an
environment to receive or supply electrons. In this context, oxic environments, as those
of river systems, are said to have a high redox potential because O2 is available as an
electron acceptor.
Principles of thermodynamics and chemical kinetics allow to obtain a model that often
does not completely describe the reality of natural systems. Chemical reactions may indeed
fail to achieve equilibrium because the products escape from the site of the rection
or because reactions involving the trasformation are very slow, so that non-equilibrium
conditions exist for long periods. Moreover, reaction rates can be sensitive to poorly understood
catalytic effects or to surface effects, while variables as concentration (a large
number of chemical species can coexist and interact concurrently), temperature and pressure
can have large gradients in natural systems. By taking into account this, data of 91
water samples have been modelled by using statistical methodologies for compositional
data. The application of log–contrast analysis has allowed to obtain statistical parameters
to be correlated with the calculated Eh values. In this way, natural conditions in which
chemical equilibrium is hypothesised, as well as underlying fast reactions, are compared
with those described by a stochastic approach
dc.description.sponsorship
Geologische Vereinigung; Institut d’Estadística de Catalunya; International Association for Mathematical Geology; Patronat de l’Escola Politècnica Superior de la Universitat de Girona; Fundació privada: Girona, Universitat i Futur; Càtedra Lluís Santaló d’Aplicacions de la Matemàtica; Consell Social de la Universitat de Girona; Ministerio de Ciencia i Tecnología.cat
dc.format.mimetype
application/pdf
dc.language.iso
eng
dc.publisher
Universitat de Girona. Departament d’Informàtica i Matemàtica Aplicada
dc.rights
Tots els drets reservats
dc.subject
dc.title
Thermodynamics and log–contrast analysis in fluid geochemistry
dc.type
info:eu-repo/semantics/conferenceObject
dc.rights.accessRights
info:eu-repo/semantics/openAccess