Chemical Thermodynamics of Tin - Volume 12 - OECD Nuclear ...

16 II Standards, conventions and contents of the tables
II.1.6
Nomenclature in log terms
It is of course clear that the arguments used in log functions must be dimensionless, and
this practice has been used in writing pressures, usually as log 10 p/bar. However, since
the units of the equilibrium constants, K m and K c , are frequently quite cumbersome, they
have been omitted in the log terms of these ( log10
K
m
and log10
K
c
) to facilitate reading
of the text.
II.1.7
Equilibrium constants
IUPAC has not explicitly defined the symbols and terminology for equilibrium
constants of reactions in aqueous solution. The NEA TDB Project has therefore adopted
the conventions that have been used in the work Stability Constants of Metal Ion
Complexes by Sillén and Martell [1964SIL/MAR], [1971SIL/MAR]. An outline is
given in the paragraphs below. Note that, for some simple reactions, there may be
different correct ways to index an equilibrium constant. It may sometimes be preferable
to indicate the number of the reaction to which the data refer, especially in cases where
several ligands are discussed that might be confused. For example, for the equilibrium:
m M + q L M m
L q
(II.4)
both β
qm ,
and β (II.4) would be appropriate, and β
qm ,
(II.4) is accepted, too. Note that,
in general, K is used for the consecutive or stepwise formation constant, and β is used
for the cumulative or overall formation constant. In the following outline, charges are
only given for actual chemical species, but are omitted for species containing general
symbols (M, L).
The expressions in sub-Sections II.1.7.1.1 through II.1.7.1.4 are expressed in
terms of (amount substance) concentrations (i.e., [X] ≡ c X and the constants are K c ;
cf. footnote f to Table II-2), but parallel nomenclature has been used in the rest of the
review for equilibria expressed using molalities (K m ) or using activities in thermodynamic
equilibrium constants ( K ). The units here
ο
for
are (mol·dm –3 ) Σ Bν B.
II.1.7.1 Protonation of a ligand
Kc
= Π
B
c ν
B
⎡
⎣HL⎤
⎦
+
r
H + Hr− 1L HrL
K1, r
=
+
⎡
⎣H ⎤⎡
⎦⎣Hr
−1L
⎤
⎦
(II.5)
⎡HL⎤
+
r
r H + L HrL
β
1, r
=
⎣ ⎦
(II.6)
+
r
⎡
⎣H
⎤
⎦
⎡
⎣L
⎤
⎦
This notation has been proposed and used by Sillén and Martell [1964SIL/MAR], but it
has been simplified later by the same authors [1971SIL/MAR] from K
1,r
to K
r
.
CHEMICAL THERMODYNAMICS OF TIN, ISBN 978-92-64-99206-1, © OECD 2012