energy is eventually converted into
heat. Since this process involves colli-
sions, the rate at which it occurs de-
pends on how frequently collisons
occur. As a result, this process occurs
much faster in liquids than in gases.
It is sometimes called collision
quenching.extractionThe separation of a
component from its mixture by selec-
tive solubility. See partition.extractive distillationA distilla-
tion technique in which a solvent is
added to the mixture in order to sep-
arate two closely boiling compo-
nents. The added solvent is usually
nonvolatile and is selected for its
ability to have different effects on
the volatilities of the components.extraordinary ray See double re-
fraction.extrinction coefÜcientSee ab-
sorption coefficient.
extrusion reaction See insertion
reaction.
Eyring, Henry(1901–81) US
chemist who worked at Princeton
and Utah. His main work was on
chemical kinetics and he is noted for
the *Eyring equation for absolute re-
action rates.Eyring equationAn equation used
extensively to describe chemical re-
actions. For a rate constant κ, it is
given by
κ= K(kT/h)exp(–∆G‡/kT),
where k is the *Boltzmann constant,
T is the thermodynamic temperature,
h is the *Planck constant, ∆G‡is the
free energy of activation, and K is a
constant called the transmission
coefÜcient, which is the probability
that a chemical reaction takes place
once the system has reached the acti-vated state. A similar equation (with-
out the K) has been used to describe
transport processes, such as diffu-
sion, thermal conductivity, and vis-
cosity in dense gases and liquids. In
these cases it is assumed that the
main kinetic process is the motion of
a molecule to a vacant site near it.
The equation is derived by assuming
that the reactants are in equilibrium
with the excited state. This assump-
tion of equilibrium is not necessarily
correct for small activation energies.
The Eyring equation is named after
Henry *Eyring, who derived it and
applied it widely in the theory of
chemical reactions and transport
processes.
E–Z conventionA convention for
the description of a molecule show-
ing cis-trans isomerism (see iso-
merism). In a molecule ABC=CDE,
where A,B,D, and E are substituent
groups, the sequence rule (see cip sys-
tem) is applied to the pair A and B to
Ünd which has priority and similarly
to the pair C and D. If the two groups
of highest priority are on the same
side of the bond then the isomer is
designated Z (from German
zusammen, together). If they are on
opposite sides the isomer is desig-
nated E (German entgegen, opposite).
The letters are used in the names
of compounds; for example (E)-
butenedioic acid (fumaric acid) and
(Z)-butenedioic acid (maleic acid). In
compounds containing two (or more)
double bonds numbers are used to
designate the bonds (e.g. (2E, 4Z)-2,4-
hexadienoic acid). The system is less
ambiguous than the cis/trans system
of describing isomers.
A- Information about the convention from
IUPAC
extraction 218e