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- Temperature, kinetic theory,
- Kinetic theory: atomic and
What is the average kinetic energy of a nitrogen molecule (N
2 ) if its
rms speed is 560 m/s? At what temperature is this
rms speed achieved?
(a) 7.29 × 10
-21 J; (b) 352K or 79ºC
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Section summary
- Kinetic theory is the atomistic description of gases as well as liquids and solids.
- Kinetic theory models the properties of matter in terms of continuous random motion of atoms and molecules.
- The ideal gas law can also be expressed as
where
is the pressure (average force per unit area),
is the volume of gas in the container,
is the number of molecules in the container,
is the mass of a molecule, and
is the average of the molecular speed squared.
- Thermal energy is defined to be the average translational kinetic energy
of an atom or molecule.
- The temperature of gases is proportional to the average translational kinetic energy of atoms and molecules.
or
- The motion of individual molecules in a gas is random in magnitude and direction. However, a gas of many molecules has a predictable distribution of molecular speeds, known as the
Maxwell-Boltzmann distribution .
Conceptual questions
Problems&Exercises
Some incandescent light bulbs are filled with argon gas. What is
for argon atoms near the filament, assuming their temperature is 2500 K?
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Average atomic and molecular speeds
are large, even at low temperatures. What is
for helium atoms at 5.00 K, just one degree above helium’s liquefaction temperature?
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(a) What is the average kinetic energy in joules of hydrogen atoms on the
surface of the Sun? (b) What is the average kinetic energy of helium atoms in a region of the solar corona where the temperature is
?
(a)
(b)
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The escape velocity of any object from Earth is 11.2 km/s. (a) Express this speed in m/s and km/h. (b) At what temperature would oxygen molecules (molecular mass is equal to 32.0 g/mol) have an average velocity
equal to Earth’s escape velocity of 11.1 km/s?
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The escape velocity from the Moon is much smaller than from Earth and is only 2.38 km/s. At what temperature would hydrogen molecules (molecular mass is equal to 2.016 g/mol) have an average velocity
equal to the Moon’s escape velocity?
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Nuclear fusion, the energy source of the Sun, hydrogen bombs, and fusion reactors, occurs much more readily when the average kinetic energy of the atoms is high—that is, at high temperatures. Suppose you want the atoms in your fusion experiment to have average kinetic energies of
. What temperature is needed?
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Suppose that the average velocity
of carbon dioxide molecules (molecular mass is equal to 44.0 g/mol) in a flame is found to be
. What temperature does this represent?
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Hydrogen molecules (molecular mass is equal to 2.016 g/mol) have an average velocity
equal to 193 m/s. What is the temperature?
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Much of the gas near the Sun is atomic hydrogen. Its temperature would have to be
for the average velocity
to equal the escape velocity from the Sun. What is that velocity?
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There are two important isotopes of uranium—
and
; these isotopes are nearly identical chemically but have different atomic masses. Only
is very useful in nuclear reactors. One of the techniques for separating them (gas diffusion) is based on the different average velocities
of uranium hexafluoride gas,
. (a) The molecular masses for
and
are 349.0 g/mol and 352.0 g/mol, respectively. What is the ratio of their average velocities? (b) At what temperature would their average velocities differ by 1.00 m/s? (c) Do your answers in this problem imply that this technique may be difficult?
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Source:
OpenStax, College physics for ap® courses. OpenStax CNX. Nov 04, 2016 Download for free at https://legacy.cnx.org/content/col11844/1.14
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