in thermal equilibrium with a third
body, then all three bodies are in
thermal equilibrium with each other.
See also enthalpy; free energy.
A
• A tutorial from the Division of Chemical
Education, Purdue University, Indiana
• Thermodynamic properties from the
committee on Data for Science and
Technology
thermodynamic temperature
See temperature.
thermoluminescence *Luminescence produced in a solid when its
temperature is raised. It arises when
free electrons and holes, trapped in a
solid as a result of exposure to ionizing radiation, unite and emit photons
of light. The process is made use of
in thermoluminescent dating, which
assumes that the number of electrons and holes trapped in a sample
of pottery is related to the length of
time that has elapsed since the pottery was Üred. By comparing the luminescence produced by heating a
piece of pottery of unknown age
with the luminescence produced by
heating similar materials of known
age, a fairly accurate estimate of the
age of an object can be made.
thermoluminescent dating See
thermoluminescence.
thermolysis (pyrolysis) The chemical decomposition of a substance by
heat. It is an important process in
chemical manufacture, such as the
thermal *cracking of hydrocarbons
in the petroleum industry.
thermometer An instrument used
for measuring the *temperature of a
substance. A number of techniques
and forms are used in thermometers
depending on such factors as the degree of accuracy required and the
range of temperatures to be measured, but they all measure temperature by making use of some property
of a substance that varies with temperature. For example, liquid-in-glass
thermometers depend on the expansion of a liquid, usually mercury or
alcohol coloured with dye. These consist of a liquid-Ülled glass bulb attached to a partially Ülled capillary
tube. In the bimetallic thermometer
the unequal expansion of two dissimilar metals that have been bonded together into a narrow strip and coiled
is used to move a pointer round a
dial. The gas thermometer, which is
more accurate than the liquid-inglass thermometer, measures the
variation in the pressure of a gas
kept at constant volume. The resistance thermometer is based on the
change in resistance of conductors or
semiconductors with temperature
change. Platinum, nickel, and copper
are the metals most commonly used
in resistance thermometers.
thermoplastic See plastics.
thermosetting See plastics.
thermostat A device that controls
the heating or cooling of a substance
in order to maintain it at a constant
temperature. It consists of a temperature-sensing instrument connected to
a switching device. When the temperature reaches a predetermined
level the sensor switches the heating
or cooling source on or off according
to a predetermined program. The
sensing thermometer is often a
bimetallic strip that triggers a simple
electrical switch. Thermostats are
used for space-heating controls, in
water heaters and refrigerators, and
to maintain the environment of a scientiÜc experiment at a constant temperature.
THF See tetrahydrofuran.
thiamin(e) See vitamin b complex.
thiazole A heterocyclic compound
525
thiazole
t
www.AzShimi.ir www.AzShimi.com
body, then all three bodies are in
thermal equilibrium with each other.
See also enthalpy; free energy.
A
• A tutorial from the Division of Chemical
Education, Purdue University, Indiana
• Thermodynamic properties from the
committee on Data for Science and
Technology
thermodynamic temperature
See temperature.
thermoluminescence *Luminescence produced in a solid when its
temperature is raised. It arises when
free electrons and holes, trapped in a
solid as a result of exposure to ionizing radiation, unite and emit photons
of light. The process is made use of
in thermoluminescent dating, which
assumes that the number of electrons and holes trapped in a sample
of pottery is related to the length of
time that has elapsed since the pottery was Üred. By comparing the luminescence produced by heating a
piece of pottery of unknown age
with the luminescence produced by
heating similar materials of known
age, a fairly accurate estimate of the
age of an object can be made.
thermoluminescent dating See
thermoluminescence.
thermolysis (pyrolysis) The chemical decomposition of a substance by
heat. It is an important process in
chemical manufacture, such as the
thermal *cracking of hydrocarbons
in the petroleum industry.
thermometer An instrument used
for measuring the *temperature of a
substance. A number of techniques
and forms are used in thermometers
depending on such factors as the degree of accuracy required and the
range of temperatures to be measured, but they all measure temperature by making use of some property
of a substance that varies with temperature. For example, liquid-in-glass
thermometers depend on the expansion of a liquid, usually mercury or
alcohol coloured with dye. These consist of a liquid-Ülled glass bulb attached to a partially Ülled capillary
tube. In the bimetallic thermometer
the unequal expansion of two dissimilar metals that have been bonded together into a narrow strip and coiled
is used to move a pointer round a
dial. The gas thermometer, which is
more accurate than the liquid-inglass thermometer, measures the
variation in the pressure of a gas
kept at constant volume. The resistance thermometer is based on the
change in resistance of conductors or
semiconductors with temperature
change. Platinum, nickel, and copper
are the metals most commonly used
in resistance thermometers.
thermoplastic See plastics.
thermosetting See plastics.
thermostat A device that controls
the heating or cooling of a substance
in order to maintain it at a constant
temperature. It consists of a temperature-sensing instrument connected to
a switching device. When the temperature reaches a predetermined
level the sensor switches the heating
or cooling source on or off according
to a predetermined program. The
sensing thermometer is often a
bimetallic strip that triggers a simple
electrical switch. Thermostats are
used for space-heating controls, in
water heaters and refrigerators, and
to maintain the environment of a scientiÜc experiment at a constant temperature.
THF See tetrahydrofuran.
thiamin(e) See vitamin b complex.
thiazole A heterocyclic compound
525
thiazole
t
www.AzShimi.ir www.AzShimi.com