4 postulates of kinetic theory 1) spherical molecules in constant, random straight-line motion 2)...
TRANSCRIPT
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4 Postulates of Kinetic Theory
1) Spherical molecules in constant, random straight-line motion
2) “Elastic” collisions3) Point masses4) No interactions
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Ideal Gas
Gas that obeys all 4 assumptions of the kinetic theory all of the time. It doesn’t exist. It’s a model.
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Real Gas
Most real gases obey the kinetic theory most of the time.
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Which assumptions of the kinetic theory hold up?
1. Spherical molecules in random, straight-line motion
2. “Elastic” collisions
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Which assumptions of the kinetic theory break
down?
1. Point masses2. No interactions
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When do the assumptions of the kinetic theory
break down?
When the gas molecules are close to each other.
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When are the gas molecules close to each
other?
At high pressure & low temperature.
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When are the gas molecules far apart from
each other?
At low pressure & high temperature.
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How do the gas molecules act when they are far apart from each
other?
Good!
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What are the properties of gases?
1. Have mass2. Take the shape & volume of their
container3. Compressible4. Diffuse (spread spontaneously)5. Exert Pressure
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Pressure
Force/Area
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Pressure results from?
Collisions of the gas molecules with the walls of the
container.
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Pressure depends on?(microscopically)
# of impacts per unit time and force of each impact
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Pressure depends on?(macroscopically)
# of gas molecules per unit volumeAnd
temperature
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Units of Pressure?
1 atm = 760 mm Hg =
760 torr = 101.3 kPa
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STP
P = 1 atmT = 0C = 273 K
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Molar Volume at STP
The volume of 1 mole of any gas at STP = 22.4 Liters
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Temperature
A measure of the avg. kinetic energy of the particles of a
substance.
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4 variables needed to completely describe a
gas-phase system?
1.Temperature2.Pressure3.Volume4.# of moles
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Boyle’s Law
For a fixed mass and temperature, the pressure-
volume product is a constant.
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Boyle’s Law
Volume of a gas varies inversely with the pressure.
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Boyle’s Law
PV = k where k = a constant
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Boyle’s Law
P1V1 = P2V2
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Graph of Boyle’s Law
Hyperbola – it’s an inverse relationship!
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Graph of Boyle’s Law, Pressure vs. Volume
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Double the pressure
Volume goes to ½ the original volume
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Triple the pressure
Volume goes to 1/3 the original volume
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Halve the pressure
Volume goes to 2 X the original volume
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Quadruple the pressure
Volume goes to 1/4 of the original volume
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What does the graph of a direct relationship look
like?
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Which temperature scale has a direct relationship to molecular velocity?
Kelvin: 0 K means 0 speed.
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Absolute Temperature Scale
Kelvin: 0 K means 0 speed.
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Graph of Volume vs. Kelvin Temperature
It’s a direct relationship.
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Math expression of relationship between
volume & Kelvin temperature
V1/T1 = V2/T2
Charles’ Law
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Verbal expression of Charles’ Law
Volume of a gas varies directly with the Kelvin temperature.
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What happens to the volume when the Kelvin temperature is doubled?
The volume doubles!
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What happens to the volume when the Kelvin temperature is tripled?
The volume triples!
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What happens to the volume when the Kelvin temperature is halved?
The volume is halved!
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What happens to the Kelvin temperature when the
volume is halved?
It’s halved!
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Graph of Pressure vs. Kelvin Temperature
It’s a direct relationship.
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Math expression for relationship between
pressure & Kelvin temperature.
P1/T1 = P2/T2
Gay-Lussac’s Law
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Verbal expression of relationship between
pressure & Kelvin temperature.
The pressure of a gas varies directly with the Kelvin temperature.
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What happens to the pressure when the Kelvin temperature is doubled?
The pressure is doubled.
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What happens to the pressure when the Kelvin temperature is halved?
The pressure is halved.
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What happens to the pressure when the Kelvin temperature is tripled?
The pressure is tripled.
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What happens to the Kelvin temperature when the pressure is doubled?
The Kelvin temperature is doubled.
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Combined Gas Law
P1V1 = P2V2 T1 T2
Same pressure & volume units on both sides. Temperature must be in Kelvins.
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What is Avogadro’s Principle?
Equal volumes of gases at the same temperature & pressure have equal numbers of molecules.
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These 2 boxes have the same:
a) Mass c) # of molecules
b) Density d) # of atoms
He N2
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What is Dalton’s Law of Partial Pressures?
Ptot = P1 + P2 + P3 + P4 + …
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At the same temperature, which of the following gases diffuses most
rapidly?
He Ne Ar Kr Xe
Lightest is fastest!
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At the same temperature, which of the following gases diffuses most
slowly?
He Ne Ar Kr Xe
Heaviest is slowest!