Chapter 17 Kinetic Theory of Gases

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Chapter 17Kinetic Theory of Gases
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17-1,Thermal Equilibrium
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If two objects are in thermal equilibrium with a
third, then they are in thermal equilibrium with
each other Zeroth Law of Thermodynamics
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Two objects in thermal equilibrium have the same
temperature
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17-2,Temperature Scales
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Celsius Scale

• Ice-Point Temperature
• Temperature of normal freezing point of water
• Steam-point Temperature
• Temperature of normal boiling point of water

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Celsius Scale

• Ice-Point Temperature
• Defined to be 0o C
• Steam-point Temperature
• Defined to be 100o C
• Temperature of human body
• 37o C

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Fahrenheit Scale

• Ice-Point Temperature
• Defined to be 32o F
• Steam-point Temperature
• Defined to be 212o F
• Fahrenheit-Celsius Conversion
• tC (5/9)(tF 32o)

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17-3, The Absolute Temperature Scale
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Gas Thermometer
The volume of the gas in B1 is kept constant by
keeping the mercury column in B2 level at the
0 mark. B2 is kept at that level by raising or
lowering B3.
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Gas Thermometer
The height h is a measure of the pressure of the
gas in B1. The change in pressure of the gas
is a measure of the change in the temperature of
the gas
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Gas Thermometer
It is found that the temperature measured using
different gases is the same provided that the
gas density is sufficiently low.
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Gas Thermometer
All gas thermometers extrapolate to the
same temperature at zero pressure
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Triple Point of Water
This is a unique, and reproducible, state in
which water, water vapor and ice can coexist.
This occurs at P 4.58 mmHg t 0.01o C
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Triple Point of Water
The ideal-gas temperature scale is defined so
that the temperature of the triple point of
water is 273.16 kelvins (K)
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Triple Point of Water
Ideal-Gas Temperature Scale
P3 pressure at triple point
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17-4The Ideal-Gas Law
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Ideal Gas Law
The pressure times the volume of a low density
gas, at constant temperature, is constant.
Robert Boyle (1627-1691)
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Ideal Gas Law
Further experimental results by Jacques Charles
(1746-1823) and Joseph Gay-Lussac (1778-1850)
showed that
The constant C must be proportional to number of
gas molecules N since doubling the volume, with P
and T constant, will double C
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Ideal Gas Law
We can therefore write
and therefore
k is called Boltzmanns constant and found to
have the value k 1.381 x 10-23 J/K for all
gases.
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Ideal Gas Law
We often measure the amount of gas in moles. A
mole (mol) of gas contains Avogadros number NA
of atoms or molecules Avogadros number NA
6.022 x 1023 is the number of carbon atoms in
12g of 12C
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Ideal Gas Law
n moles of gas contains
atoms or molecules.
Therefore
where R is the gas constant
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Results for Real Gases
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Ideal Gas Law
The law
is approximately true for real gases at
low pressure and density. An ideal gas is
defined as a gas that obeys this law exactly.
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Ideal Gas Law