energy is eventually converted into
heat. Since this process involves collisions, the rate at which it occurs depends on how frequently collisons
occur. As a result, this process occurs
much faster in liquids than in gases.
It is sometimes called collision
quenching.
extraction The separation of a
component from its mixture by selective solubility. See partition.
extractive distillation A distillation technique in which a solvent is
added to the mixture in order to separate two closely boiling components. 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 refraction.
extrinction coefÜcient See absorption 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 reaction rates.
Eyring equation An equation used
extensively to describe chemical reactions. 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 activated state. A similar equation (without the K) has been used to describe
transport processes, such as diffusion, thermal conductivity, and viscosity 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 assumption 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 convention A convention for
the description of a molecule showing cis-trans isomerism (see isomerism). In a molecule ABC=CDE,
where A,B,D, and E are substituent
groups, the sequence rule (see cip system) 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 designated 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)-2,4hexadienoic acid). The system is less
ambiguous than the cis/trans system
of describing isomers.
A
• Information about the convention from
IUPAC
extraction
218
e
www.AzShimi.ir www.AzShimi.com
heat. Since this process involves collisions, the rate at which it occurs depends on how frequently collisons
occur. As a result, this process occurs
much faster in liquids than in gases.
It is sometimes called collision
quenching.
extraction The separation of a
component from its mixture by selective solubility. See partition.
extractive distillation A distillation technique in which a solvent is
added to the mixture in order to separate two closely boiling components. 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 refraction.
extrinction coefÜcient See absorption 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 reaction rates.
Eyring equation An equation used
extensively to describe chemical reactions. 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 activated state. A similar equation (without the K) has been used to describe
transport processes, such as diffusion, thermal conductivity, and viscosity 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 assumption 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 convention A convention for
the description of a molecule showing cis-trans isomerism (see isomerism). In a molecule ABC=CDE,
where A,B,D, and E are substituent
groups, the sequence rule (see cip system) 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 designated 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)-2,4hexadienoic acid). The system is less
ambiguous than the cis/trans system
of describing isomers.
A
• Information about the convention from
IUPAC
extraction
218
e
www.AzShimi.ir www.AzShimi.com