67 binary acid
b
strate for further adsorption. The
BET isotherm (named after S.
Brunauer, P. Emmett, and E. Teller)
has the form:
V/Vmon= cz/{(1 – z)[1 – (1 – c)z]},where z = p/p(pis the vapour pres-
sure above a macroscopically thick
layer of liquid on the surface), Vmonis
the volume that corresponds to the
surface being covered by a mono-
layer, V and p are the volume and
pressure of the gas respectively, and c
is a constant. In the BET isotherm,
the isotherm rises indeÜnitely at
high pressures (in contrast to the
Langmuir isotherm). It provides a
useful approximation over some
ranges of pressure but underesti-
mates adsorption for low pressures
and overestimates adsorption for
high pressures.
BHC See benzene hexachloride.
bicarbonateSee hydrogencarbon-
ate.
bicarbonate of sodaSee sodium
hydrogencarbonate.bifurcation A phenomenon in dy-
namical systems in which the num-
ber of solutions for a type of
behaviour suddenly changes when
one of the parameters deÜning the
system reaches a critical value. Bifur-
cations can be depicted in a bifurca-
tion diagram in which one axis of a
graph is a variable of the system and
the other axis is a parameter that can
bring about bifurcations. In many
systems a whole series of bifurca-
tions occur, called bifurcation cas-
cades. In certain cases these
bifurcation cascades can lead to
chaotic reactions.bimolecular reaction A step in a
chemical reaction that involves two
molecules. See molecularity.binaryDescribing a compound or
alloy formed from two elements.binary acidAn *acid in which the
acidic hydrogen atom(s) are bound di-HHHNNNO
HHH CCCRNNNRHHHRH
CCCOOOOCCCRHNNNHHHOCCChydrogen bond
amino-acid side chainCCC
OHHH
RRNNNHHHOCCCCCCRHHHHHHOOOCCCCCC
NNN HHH
NNN NNN
CCC
NHHHOOO
RHNNN
HH
OCROOOCCCRCCC
NNNHHHRHHHOCCCRCCCOOOHHHNNNCCCOOORHHHNNNHHHRHHH CCCNNNHHH
ORCOOOHNNNN
•
- •
- ••
- •
- •
- •
- •
HHH- •
H
•
- ••
R
CCCCCC
CCCHHHCCCCCC
CCCCCCCCCHHHCCCCCCHHHCCCCCC=Beta sheet