(and phenol) by a gas-phase reaction
between benzene vapour, hydrogen
chloride, and oxygen (air) at 230°C:
2C 6 H 6 + 2HCl + O 2 → 2H 2 O +
2C 6 H 5 Cl
The catalyst is copper(II) chloride.
The chlorobenzene is mainly used
for making phenol by the reaction
C 6 H 5 Cl + H 2 O → HCl + C 6 H 5 OH
This reaction proceeds at 430°C with
a silicon catalyst. The process was invented by the German chemist Fritz
Raschig (1863–1928).
Raschig synthesis See hydrazine.
RasMol A commonly used program
for visualizing molecules. It can be
used with a range of Üle formats and
the display can be choosen (e.g. wireframe, ball-and-stick, space Ülling,
etc.). The original version was written by Roger Sayle of Glaxo around
1990. It is freely available.
A
• A downloadable version of RasMol from
the website of the University of
Massachusetts Amherst
rate constant (velocity constant)
Symbol k. The constant in an expression for the rate of a chemical reaction in terms of concentrations (or
activities). For instance, in a simple
unimolecular reaction A → B, the
rate is proportional to the concentration of A, i.e. rate = k[A], where k is
the rate constant, which depends on
the temperature. The equation is the
rate equation of the reaction, and its
form depends on the reaction mechanism.
rate-determining step The slowest step in a chemical reaction that
involves a number of steps. In such
reactions, there is often a single step
that is appreciably slower than the
other steps, and the rate of this determines the overall rate of the reaction.
rationalized Planck constant See
planck constant.
rationalized units A system of
units in which the deÜning equations
have been made to conform to the
geometry of the system in a logical
way. Thus equations that involve circular symmetry contain the factor
2π, while those involving spherical
symmetry contain the factor 4π. *SI
units are rationalized; c.g.s. units are
unrationalized.
Rayleigh, Lord (John William
Strutt; 1842–1919) British physicist,
who built a private laboratory after
working at Cambridge University.
His work in this laboratory included
the discovery of *Rayleigh scattering
of electromagnetic radiation. He also
worked in acoustics, electricity, and
optics, as well as collaborating with
William *Ramsay on the discovery of
argon. He was awarded the 1904
Nobel Prize for physics.
Rayleigh scattering Scattering of
electromagnetic radiation by molecules in which the frequency of the
scattered radiation is unchanged.
This type of scattering was analysed
by Lord *Rayleigh in his papers in
the late 19th century, which showed
that the blue colour of the sky is a result of this type of light scattering,
with molecules of the atmosphere of
the earth scattering light from the
sun.
rayon A textile made from cellulose. There are two types, both made
from wood pulp. In the viscose
process, the pulp is dissolved in carbon disulphide and sodium hydroxide to give a thick brown liquid
containing cellulose xanthate. The
liquid is then forced through Üne
nozzles into acid, where the xanthate
is decomposed and a cellulose Ülament is produced. The product is viscose rayon. In the acetate process
455
rayon
r
www.AzShimi.ir www.AzShimi.com
between benzene vapour, hydrogen
chloride, and oxygen (air) at 230°C:
2C 6 H 6 + 2HCl + O 2 → 2H 2 O +
2C 6 H 5 Cl
The catalyst is copper(II) chloride.
The chlorobenzene is mainly used
for making phenol by the reaction
C 6 H 5 Cl + H 2 O → HCl + C 6 H 5 OH
This reaction proceeds at 430°C with
a silicon catalyst. The process was invented by the German chemist Fritz
Raschig (1863–1928).
Raschig synthesis See hydrazine.
RasMol A commonly used program
for visualizing molecules. It can be
used with a range of Üle formats and
the display can be choosen (e.g. wireframe, ball-and-stick, space Ülling,
etc.). The original version was written by Roger Sayle of Glaxo around
1990. It is freely available.
A
• A downloadable version of RasMol from
the website of the University of
Massachusetts Amherst
rate constant (velocity constant)
Symbol k. The constant in an expression for the rate of a chemical reaction in terms of concentrations (or
activities). For instance, in a simple
unimolecular reaction A → B, the
rate is proportional to the concentration of A, i.e. rate = k[A], where k is
the rate constant, which depends on
the temperature. The equation is the
rate equation of the reaction, and its
form depends on the reaction mechanism.
rate-determining step The slowest step in a chemical reaction that
involves a number of steps. In such
reactions, there is often a single step
that is appreciably slower than the
other steps, and the rate of this determines the overall rate of the reaction.
rationalized Planck constant See
planck constant.
rationalized units A system of
units in which the deÜning equations
have been made to conform to the
geometry of the system in a logical
way. Thus equations that involve circular symmetry contain the factor
2π, while those involving spherical
symmetry contain the factor 4π. *SI
units are rationalized; c.g.s. units are
unrationalized.
Rayleigh, Lord (John William
Strutt; 1842–1919) British physicist,
who built a private laboratory after
working at Cambridge University.
His work in this laboratory included
the discovery of *Rayleigh scattering
of electromagnetic radiation. He also
worked in acoustics, electricity, and
optics, as well as collaborating with
William *Ramsay on the discovery of
argon. He was awarded the 1904
Nobel Prize for physics.
Rayleigh scattering Scattering of
electromagnetic radiation by molecules in which the frequency of the
scattered radiation is unchanged.
This type of scattering was analysed
by Lord *Rayleigh in his papers in
the late 19th century, which showed
that the blue colour of the sky is a result of this type of light scattering,
with molecules of the atmosphere of
the earth scattering light from the
sun.
rayon A textile made from cellulose. There are two types, both made
from wood pulp. In the viscose
process, the pulp is dissolved in carbon disulphide and sodium hydroxide to give a thick brown liquid
containing cellulose xanthate. The
liquid is then forced through Üne
nozzles into acid, where the xanthate
is decomposed and a cellulose Ülament is produced. The product is viscose rayon. In the acetate process
455
rayon
r
www.AzShimi.ir www.AzShimi.com