synthesizing organic compounds in
which the materials used are mixed
together in a single vessel and allowed to react, rather than conducting the reaction in a sequence of
separate stages.
onium ion An ion formed by
adding a proton to a neutral molecule, e.g. the hydroxonium ion
(H 3 O
+
) or the ammonium ion (NH 4
+ ).
Onsager relations In a system
that is not at equilibrium, various
changes are occurring. For example,
there may be a Ûow of energy from
one part of the system to another
and, at the same time, a Ûow of mass
(diffusion). Flows of this type are coupled, i.e. each depends on the other.
Equations exist of the type
J 1 = L 11 X 1 + L 12 X 2
J 2 = L 21 X 1 + L 22 X 2
Here, J 1 is the Ûow of energy and J 2
the Ûow of matter. X 1 is the ‘force’
producing energy Ûow and X 2 that
producing matter Ûow. L 11 is the
coefÜcient for thermal conductance
and L 22 the coefÜcient for diffusion.
The coefÜcients L 12 and L 21 represent
coupling of the Ûows with each
other. Equations of this type can be
generalized to any number of Ûows
and are known as the phenomenological relations. In Onsager’s theory
the coupling coefÜcients are equal,
i.e. L 12 = L 21 , etc. These are known as
reciprocal relations. It follows that:
(∂J 1 /∂X 2 ) X1 = (∂J 2 /∂X 1 ) X2 .
The theory was developed by the
Swedish physicist Lars Onsager in
1931.
opal A hydrous amorphous form of
silica. Many varieties of opal occur,
some being prized as gemstones.
Common opal is usually milk white
but the presence of impurities may
colour it yellow, green, or red. Precious opals, which are used as gemstones, display the property of
opalescence – a characteristic internal play of colours resulting from the
interference of light rays within the
stone. Black opal has a black background against which the colours are
displayed. The chief sources of precious opals are Australia and Mexico.
Geyserite is a variety deposited by
geysers or hot springs. Another variety, diatomite, is made up of the
skeletons of diatoms.
open chain See chain.
open-hearth process A traditional but now obsolete method for
manufacturing steel by heating together scrap, pig iron, etc., in a refractory-lined shallow open furnace
heated by burning producer gas in
air. It has been replaced by the
*basic-oxygen process.
operator A mathematical entity
that performs a speciÜc operation on
a function to transform the function
into another function. For example,
the square root sign √ and the differentiation symbol d/dx are operators.
opiate One of a group of drugs derived from *opium, which depress
brain function (a narcotic action).
Opiates include *morphine and its
synthetic derivatives, such as *heroin
and codeine. They are used in medicine chieÛy to relieve pain, but the
use of morphine and heroin is
strictly controlled since they can
cause drug dependence and tolerance.
opioid Any one of a group of substances that produce pharmacological and physiological effects similar
to those of morphine. Opioids are
not necessarily structurally similar to
morphine, although a subgroup of
opioids, the *opiates, are morphinederived compounds.
opium A substance obtained from
onium ion
384
o
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which the materials used are mixed
together in a single vessel and allowed to react, rather than conducting the reaction in a sequence of
separate stages.
onium ion An ion formed by
adding a proton to a neutral molecule, e.g. the hydroxonium ion
(H 3 O
+
) or the ammonium ion (NH 4
+ ).
Onsager relations In a system
that is not at equilibrium, various
changes are occurring. For example,
there may be a Ûow of energy from
one part of the system to another
and, at the same time, a Ûow of mass
(diffusion). Flows of this type are coupled, i.e. each depends on the other.
Equations exist of the type
J 1 = L 11 X 1 + L 12 X 2
J 2 = L 21 X 1 + L 22 X 2
Here, J 1 is the Ûow of energy and J 2
the Ûow of matter. X 1 is the ‘force’
producing energy Ûow and X 2 that
producing matter Ûow. L 11 is the
coefÜcient for thermal conductance
and L 22 the coefÜcient for diffusion.
The coefÜcients L 12 and L 21 represent
coupling of the Ûows with each
other. Equations of this type can be
generalized to any number of Ûows
and are known as the phenomenological relations. In Onsager’s theory
the coupling coefÜcients are equal,
i.e. L 12 = L 21 , etc. These are known as
reciprocal relations. It follows that:
(∂J 1 /∂X 2 ) X1 = (∂J 2 /∂X 1 ) X2 .
The theory was developed by the
Swedish physicist Lars Onsager in
1931.
opal A hydrous amorphous form of
silica. Many varieties of opal occur,
some being prized as gemstones.
Common opal is usually milk white
but the presence of impurities may
colour it yellow, green, or red. Precious opals, which are used as gemstones, display the property of
opalescence – a characteristic internal play of colours resulting from the
interference of light rays within the
stone. Black opal has a black background against which the colours are
displayed. The chief sources of precious opals are Australia and Mexico.
Geyserite is a variety deposited by
geysers or hot springs. Another variety, diatomite, is made up of the
skeletons of diatoms.
open chain See chain.
open-hearth process A traditional but now obsolete method for
manufacturing steel by heating together scrap, pig iron, etc., in a refractory-lined shallow open furnace
heated by burning producer gas in
air. It has been replaced by the
*basic-oxygen process.
operator A mathematical entity
that performs a speciÜc operation on
a function to transform the function
into another function. For example,
the square root sign √ and the differentiation symbol d/dx are operators.
opiate One of a group of drugs derived from *opium, which depress
brain function (a narcotic action).
Opiates include *morphine and its
synthetic derivatives, such as *heroin
and codeine. They are used in medicine chieÛy to relieve pain, but the
use of morphine and heroin is
strictly controlled since they can
cause drug dependence and tolerance.
opioid Any one of a group of substances that produce pharmacological and physiological effects similar
to those of morphine. Opioids are
not necessarily structurally similar to
morphine, although a subgroup of
opioids, the *opiates, are morphinederived compounds.
opium A substance obtained from
onium ion
384
o
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