The term
selectivity (
) is used to describe the relative rates of two or more competing reactions on a
catalyst. Such
competition includes cases of different reactants undergoing
simultaneous reactions or of a single reactant taking part in two or more reactions. For the latter case,
may be defined in two ways. The first of these defines a fractional
selectivity,
, for each product by the equation
The second defines relative selectivities,
, for each pair of products by
In each case,
and
are the rates of increase of the
extent of reactions i and
j respectively, i.e.
and
,
where
and
are the extents of reactions
and
respectively.
Source:
PAC, 1976, 46, 71
(Manual of Symbols and Terminology for Physicochemical Quantities and Units - Appendix II. Definitions, Terminology and Symbols in Colloid and Surface Chemistry. Part II: Heterogeneous Catalysis)
on page 81
