mixed copper–iron sulphide, CuFeS 2 ,
crystallizing in the tetragonal system; the principal ore of copper. It is
similar in appearance to pyrite and
gold. It crystallizes in igneous rocks
and hydrothermal veins associated
with the upper parts of acid igneous
intrusions. Chalcopyrite is the most
widespread of the copper ores, occurring, for example, in Cornwall (UK),
Sudbury (Canada), Chile, Tasmania
(Australia), and Rio Tinto (Spain).
chalk A very Üne-grained white
rock composed of the skeletal remains of microscopic sea creatures,
such as plankton, and consisting
largely of *calcium carbonate
(CaCO 3 ). It is used in toothpaste and
cosmetics. It should not be confused
with blackboard ‘chalk’, which is
made from calcium sulphate.
change of phase (change of state)
A change of matter in one physical
*phase (solid, liquid, or gas) into another. The change is invariably accompanied by the evolution or
absorption of energy.
chaos Unpredictable and apparently random behaviour arising in a
system that is governed by deterministic laws (i.e. laws that, given the
state of the system at a given time,
uniquely determine the state at any
other time). Chaotic dynamics are
widespread in nature: examples are
the turbulent Ûow of Ûuids, the dynamics of planetary moons, oscillations in electrical circuits, and the
long-term unpredictability of the
weather. In such situations, chaos
arises because the mathematical
equations expressing the (deterministic) laws in question are nonlinear
and extremely sensitive to the initial
conditions. It is impossible to specify
data at a given time to a sufÜcient degree of precision to be able to predict
the future behaviour of the system
because two pieces of initial data differing by even a very small amount
will give widely different results at a
later time. Originally, the theory was
introduced to describe unpredictability in meteorology, as exempliÜed by
the butterÛy effect. It has been suggested that the dynamical equations
governing the weather are so sensitive to the initial data that whether
or not a butterÛy Ûaps its wings in
one part of the world may make the
difference between a tornado occurring or not occurring in some other
part of the world. In chemistry,
chaos theory has been used to explain oscillatory (clock) reactions,
such as the *B–Z reaction, and
chaotic reactions.
chaotic dynamics See chaos.
chaotic reaction A type of chemical reaction in which the concentrations of reactants show chaotic
behaviour. This may occur when the
reaction involves a large number of
complex interlinked steps. Under
such conditions, it is possible for the
reaction to display unpredictable
changes with time. See also bistability; oscillating reaction.
charcoal A porous form of carbon
produced by the destructive distillation of organic material. Charcoal
from wood is used as a fuel. All forms
of charcoal are porous and are used
for adsorbing gases and purifying
and clarifying liquids. There are several types depending on the source.
Charcoal from coconut shells is a particularly good gas adsorbent. Animal
charcoal (or bone black) is made by
heating bones and dissolving out the
calcium phosphates and other mineral salts with acid. It is used in sugar
reÜning. Activated charcoal is charcoal that has been activated for adsorption by steaming or by heating
in a vacuum.
113
charcoal
c
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crystallizing in the tetragonal system; the principal ore of copper. It is
similar in appearance to pyrite and
gold. It crystallizes in igneous rocks
and hydrothermal veins associated
with the upper parts of acid igneous
intrusions. Chalcopyrite is the most
widespread of the copper ores, occurring, for example, in Cornwall (UK),
Sudbury (Canada), Chile, Tasmania
(Australia), and Rio Tinto (Spain).
chalk A very Üne-grained white
rock composed of the skeletal remains of microscopic sea creatures,
such as plankton, and consisting
largely of *calcium carbonate
(CaCO 3 ). It is used in toothpaste and
cosmetics. It should not be confused
with blackboard ‘chalk’, which is
made from calcium sulphate.
change of phase (change of state)
A change of matter in one physical
*phase (solid, liquid, or gas) into another. The change is invariably accompanied by the evolution or
absorption of energy.
chaos Unpredictable and apparently random behaviour arising in a
system that is governed by deterministic laws (i.e. laws that, given the
state of the system at a given time,
uniquely determine the state at any
other time). Chaotic dynamics are
widespread in nature: examples are
the turbulent Ûow of Ûuids, the dynamics of planetary moons, oscillations in electrical circuits, and the
long-term unpredictability of the
weather. In such situations, chaos
arises because the mathematical
equations expressing the (deterministic) laws in question are nonlinear
and extremely sensitive to the initial
conditions. It is impossible to specify
data at a given time to a sufÜcient degree of precision to be able to predict
the future behaviour of the system
because two pieces of initial data differing by even a very small amount
will give widely different results at a
later time. Originally, the theory was
introduced to describe unpredictability in meteorology, as exempliÜed by
the butterÛy effect. It has been suggested that the dynamical equations
governing the weather are so sensitive to the initial data that whether
or not a butterÛy Ûaps its wings in
one part of the world may make the
difference between a tornado occurring or not occurring in some other
part of the world. In chemistry,
chaos theory has been used to explain oscillatory (clock) reactions,
such as the *B–Z reaction, and
chaotic reactions.
chaotic dynamics See chaos.
chaotic reaction A type of chemical reaction in which the concentrations of reactants show chaotic
behaviour. This may occur when the
reaction involves a large number of
complex interlinked steps. Under
such conditions, it is possible for the
reaction to display unpredictable
changes with time. See also bistability; oscillating reaction.
charcoal A porous form of carbon
produced by the destructive distillation of organic material. Charcoal
from wood is used as a fuel. All forms
of charcoal are porous and are used
for adsorbing gases and purifying
and clarifying liquids. There are several types depending on the source.
Charcoal from coconut shells is a particularly good gas adsorbent. Animal
charcoal (or bone black) is made by
heating bones and dissolving out the
calcium phosphates and other mineral salts with acid. It is used in sugar
reÜning. Activated charcoal is charcoal that has been activated for adsorption by steaming or by heating
in a vacuum.
113
charcoal
c
www.AzShimi.ir www.AzShimi.com