is the number of degrees of freedom
of the particles. This new concept led
to Bose–Einstein statistics, and for
particles obeying the Pauli exclusion
principle, to Fermi–Dirac statistics.
steam distillation A method of
distilling liquids that are immiscible
with water by bubbling steam
through them. It depends on the fact
that the vapour pressure (and hence
the boiling point) of a mixture of two
immiscible liquids is lower than the
vapour pressure of either pure liquid.
steam point The temperature at
which the maximum vapour pressure of water is equal to the standard
atmospheric pressure (101 325 Pa).
On the Celsius scale it has the value
100°C.
stearate (octadecanoate) A salt or
ester of stearic acid.
stearic acid (octadecanoic acid)
A solid saturated *fatty acid,
CH 3 (CH 2 ) 16 COOH; r.d. 0.94; m.p.
71.5–72°C; b.p. 360°C (with decomposition). It occurs widely (as *glycerides) in animal and vegetable fats.
steel Any of a number of alloys consisting predominantly of iron with
varying proportions of carbon (up
to 1.7%) and, in some cases, small
quantities of other elements (alloy
steels), such as manganese, silicon,
chromium, molybdenum, and nickel.
Steels containing over 11–12% of
chromium are known as *stainless
steels.
Carbon steels exist in three stable
crystalline phases: ferrite has a bodycentred cubic crystal, austenite has a
face-centred cubic crystal, and cementite has an orthorhombic crystal.
Pearlite is a mixture of ferrite and cementite arranged in parallel plates.
The phase diagram shows how the
phases form at different temperatures and compositions.
Steels are manufactured by the
*basic-oxygen process (L–D process),
which has largely replaced the
*Bessemer process and the *openhearth process, or in electrical furnaces.
503
stereoisomerism
s
960
920
880
840
800
760
720
680
640
600
temperature (°C)
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
austenite austenite austenite
austenite +
austenite +
austenite +
cementite cementite cementite
cementite +
cementite +
cementite +
pearlite pearlite pearlite
ferrite +
ferrite +
ferrite +
pearlite pearlite pearlite
ferrite +
ferrite +
ferrite +
austenite austenite austenite
carbon (%)
Steel
step A single stage in a chemical reaction. For example, the addition of
hydrogen chloride to ethene involves
three steps:
HCl → H
+ + Cl
–
H
+ + C 2 H 4 → CH 3 CH 2
+
CH 3 CH 2
+ + Cl
–
→ CH 3 CH 2 Cl
steradian Symbol sr. The dimensionless (supplementary) *SI unit of
solid angle equal to the solid angle
that encloses a surface on a sphere
equal to the square of the radius of
the sphere.
stere A unit of volume equal to
1 m
3 . It is not now used for scientiÜc
purposes.
stereochemistry The branch of
chemistry concerned with the structure of molecules and the way the
arrangement of atoms and groups affects the chemical properties.
stereoisomerism See isomerism.
www.AzShimi.ir www.AzShimi.com
of the particles. This new concept led
to Bose–Einstein statistics, and for
particles obeying the Pauli exclusion
principle, to Fermi–Dirac statistics.
steam distillation A method of
distilling liquids that are immiscible
with water by bubbling steam
through them. It depends on the fact
that the vapour pressure (and hence
the boiling point) of a mixture of two
immiscible liquids is lower than the
vapour pressure of either pure liquid.
steam point The temperature at
which the maximum vapour pressure of water is equal to the standard
atmospheric pressure (101 325 Pa).
On the Celsius scale it has the value
100°C.
stearate (octadecanoate) A salt or
ester of stearic acid.
stearic acid (octadecanoic acid)
A solid saturated *fatty acid,
CH 3 (CH 2 ) 16 COOH; r.d. 0.94; m.p.
71.5–72°C; b.p. 360°C (with decomposition). It occurs widely (as *glycerides) in animal and vegetable fats.
steel Any of a number of alloys consisting predominantly of iron with
varying proportions of carbon (up
to 1.7%) and, in some cases, small
quantities of other elements (alloy
steels), such as manganese, silicon,
chromium, molybdenum, and nickel.
Steels containing over 11–12% of
chromium are known as *stainless
steels.
Carbon steels exist in three stable
crystalline phases: ferrite has a bodycentred cubic crystal, austenite has a
face-centred cubic crystal, and cementite has an orthorhombic crystal.
Pearlite is a mixture of ferrite and cementite arranged in parallel plates.
The phase diagram shows how the
phases form at different temperatures and compositions.
Steels are manufactured by the
*basic-oxygen process (L–D process),
which has largely replaced the
*Bessemer process and the *openhearth process, or in electrical furnaces.
503
stereoisomerism
s
960
920
880
840
800
760
720
680
640
600
temperature (°C)
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
austenite austenite austenite
austenite +
austenite +
austenite +
cementite cementite cementite
cementite +
cementite +
cementite +
pearlite pearlite pearlite
ferrite +
ferrite +
ferrite +
pearlite pearlite pearlite
ferrite +
ferrite +
ferrite +
austenite austenite austenite
carbon (%)
Steel
step A single stage in a chemical reaction. For example, the addition of
hydrogen chloride to ethene involves
three steps:
HCl → H
+ + Cl
–
H
+ + C 2 H 4 → CH 3 CH 2
+
CH 3 CH 2
+ + Cl
–
→ CH 3 CH 2 Cl
steradian Symbol sr. The dimensionless (supplementary) *SI unit of
solid angle equal to the solid angle
that encloses a surface on a sphere
equal to the square of the radius of
the sphere.
stere A unit of volume equal to
1 m
3 . It is not now used for scientiÜc
purposes.
stereochemistry The branch of
chemistry concerned with the structure of molecules and the way the
arrangement of atoms and groups affects the chemical properties.
stereoisomerism See isomerism.
www.AzShimi.ir www.AzShimi.com