chemical markup language
(CML)A markup language used to
express chemical information. CML is
an extension of XML (extensible
markup language), which is widely
used to store and transfer text. A par-
ticular feature of XML is the use of
tags to identify different types of in-
formation. These are commonly in
angle brackets. In the text version of
this dictionary, for example, head-
words are surrounded by the tags
<hw>...</hw>, cross references are
identiÜed by <xr>...</xr>, etc. In
CML, there are tags for many differ-
ent types of chemical information.
For example, structures can be repre-
sented by tagged data giving the
atoms and their coordinates in two
or three dimensions. Reactions can
also be indicated, as well as data for
spectra and other properties.
A- An FAQ produced by the Chemistry
Department, Cambridge University
chemical potentialSymbol: μ. For
a given component in a mixture, the
coefÜcient ∂G/∂n, where G is the
Gibbs free energy and n the amount
of substance of the component. The
chemical potential is the change in
Gibbs free energy with respect to
change in amount of the component,
with pressure, temperature, and
amounts of other components being
constant. Components are in equilib-
rium if their chemical potentials are
equal.chemical reaction A change in
which one or more chemical el-
ements or compounds (the reactants)
form new compounds (the products).
All reactions are to some extent re-
versible; i.e. the products can also
react to give the original reactants.
However, in many cases the extent of
this back reaction is negligibly small,
and the reaction is regarded as irre-
versible.chemical shiftA change in the
normal wavelength of absorption or
emission of electromagnetic wave-
length in a process in which there is
a nuclear energy change (as in the
*Mössbauer effect and *nuclear mag-
netic resonance) or a change in elec-
tron energy levels in the inner shells
of an atom (as in X-ray *photoelec-
tron spectroscopy).chemical warfare The use of toxic
chemical substances in warfare or
military operations. A large number
of chemicals have been designed or
used for warfare, including pul-
monary agents (chlorine, *carbonyl
chloride, *diphosgene), blister
agents, (*lewisite, *sulphur mustard,
*nitrogen mustard), and the *nerve
agents. Chemical warfare agents are
classiÜed as weapons of mass destruc-
tion by the United Nations. See also
chemical weapons convention.
Chemical Weapons Convention
An agreement dating from 1993 on
the production, stockpiling, and use
of chemical weapons (see chemical
warfare). It came into force in 1997
and is administered by the Organiza-
tion for the Prohibition of Chemical
Weapons (OPCW).
A- The OPCW website, giving details of the
convention
chemiluminescenceSee lumines-
cence.chemiosmotic theoryA theory
postulated by the British biochemist
Peter Mitchell (1920–92) to explain
the formation of ATP in the mito-
chondrial *electron transport chain.
As electrons are transferred along
the electron carrier system in the
inner mitochondrial membrane, hy-
drogen ions (protons) are actively
transported (via *hydrogen carriers)
into the space between the inner and
outer mitochondrial membranes,chemical markup language 118c