GAS LAWS
Properties of Gases
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Composed of randomly scattered particles
No definite _________ or ___________
Spread out to fill the space of their container
Lack intermolecular forces that hold liquids and solids
together (ideally)
Molecules move in a straight line and only change direction
after hitting another molecule or the wall of the container
Can be compressed easily (because of all that
_________________)
Exert ______________ on its surroundings (created by
molecules hitting the surface)
Kinetic Molecular Theory
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Gases are made of particles in rapid, random motion.
Not affected by the force of gravity in a container
(do not fall to the bottom)
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The gas is mostly ___________________.
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Collisions are ___________ (no loss of kinetic energy).
Ideal vs Real Gases
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____________ gases follow KMT
_________ gases come close (especially at high
temperatures and low pressures)
 Small
attractions between particles can be found
Pressure
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Created by gas molecules bouncing off the surface of
an object
Defined as: Force per unit area (F/A)
SI Unit is pascal (Pa) which equals N/m2
Pascal unit is small so often _____ is used instead
Other pressure units
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Atmosphere (atm)
mm of Hg (mmHg) and in of Hg (in Hg)
Torr
bar and millibar (mb)
Pounds per square inch (lb/in2 or psi)
Converting Between Pressure Units
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All of these are equal to each other
 101.325
1
kPa
atm
 760 mmHg
 760 Torr
 29.921 in Hg
 1.01325 bar
 14.696 psi
Pressure Conversions
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If the pressure inside a container is measured at
1.22 atm, what is the pressure in mm Hg?
If a pressure is given as 720 Torr, what is the
pressure in kPa?
Atmospheric Pressure
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Pressure from gas
particles in the
atmosphere
Measuring Pressure
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Barometer
Device measuring atmospheric pressure
 Consists of a tube of mercury being placed in bowl of
mercury
 Mercury will flow into the bowl until the pressure from the
height of the column equals the atmospheric pressure
pressing on the mercury in the bowl
 The height of the mercury column
is measured
 At sea level, atmospheric pressure is
____________________
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Measuring Pressure (cont)
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Manometer
Measures the pressure of other gases
 ___________-end manometers
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 Mercury
rests in a U-shaped tube
 Without gas- mercury level is equal on
both sides
 With gas- mercury level will rise on the
far side
 Gas pressure is represented by the
difference between the two heights

__________________
 Greater
pressure
the difference the greater the
Measuring Pressure (cont)
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________-end manometers
 Mercury
rests in a U-shaped tube
 Without gas or with gas whose
pressure is lower than atmosphericmercury level will rise on side away
from open end

__________________
 With
gas whose pressure is equal to
atmospheric- mercury level is equal
on both sides

________________
 With
gas whose pressure is higher
than atmospheric- mercury level will
rise on the far side

_______________________
Manometer Problems
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In a closed-ended manometer, the mercury column in the arm is
raised to a height of 780 mm above the other side, what is the
pressure of the gas in atm?
In an open-ended manometer, the mercury column in the
atmospheric arm is 28.2 mm lower than the other side. If the
atmospheric pressure is 762 mm Hg, what is the pressure of the
gas attached to manometer?
Dalton’s Law of Partial Pressures
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Many gases are actually mixtures of different types of
gases (like air)
States: The total pressure exerted by a mixture of
gases is equal to the sum of the partial pressures
exerted by the separate gases.
In other words:
Ptotal = P1 + P2 + P3 …
Collecting Gases over Water
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A method of collecting and measuring gases produced
as a product of a reaction
Relies on water displacement.
Gas sample will actually contain gas collected and
water vapor
Pdry gas = Ptotal – Pwater vapor
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This is just a rearrangement of
Ptotal = Pdry gas + Pwater vapor
Water vapor pressure is dependent
on the water temperature
Partial Pressure Problems
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A container holds three gases (oxygen, carbon dioxide, and helium).
The partial pressures of the gases are 2.00 atm, 3.00 atm, and
4.00 atm respectfully. What is the total pressure in the container?
What is the partial pressure of oxygen in air at 770 Torr and
containing 21% of O2?
If 60.0 L of nitrogen is collected over water at 40.0°C when the
atmospheric pressure is 760.0 mm Hg, what is the partial pressure
of the nitrogen? The water vapor pressure at 40.0°C is 55.3 mm
Hg.
Ideal Gas Law
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Gives information about a gas at a single time point
R= (PV)/(nT)
R = 0.08206 L atm mol-1 K-1
 P = ___________
 V = ___________
 n = ________________
 T = ________________
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 TemperatureK
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= Temperature°C + 273.15
Can also be rewritten M= (mRT)/PV
n has been replaced with m/M
 m = _______________
 M = ______________________
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STP
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Standard Temperature and Pressure
 Temperature
is ______________
 Pressure is ______________
Ideal Gas Law Problems
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If 25g of oxygen gas is placed in a 2 liter container at
a temperature of 292 K, what is the pressure in the
container?
What is the molar mass of a gas when 3.84g of the gas
is placed in a 570mL container at STP?
Reactions with Gases
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Ideal Gas Law can be used to find the number of
__________ reacted or produced.
_______________ can be used to get information
about other reactants or products.
Conditions for the equations such as _________ and
_____________ and given in the problem
At STP only, conversion factor _____________ can
be used
Gas Densities
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Very _________ compared to solids and liquids
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Often given in _______ instead of g/ml
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D = m/V = (MP)/RT
Gas Density Problems
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What is the density of oxygen gas at STP?
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What is the mass of 3.2 L of carbon dioxide at STP?
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What would the volume be of 367g of C2H6 at 765 mm Hg and
Combined Gas Law
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Gives information about a gas at two time points
(P1V1)/(n1T1) = (P2V2)/(n2T2)
 1-
Values at first time point
 2- Values at second time point
 P and V can be in any units but they must match on both
sides
 n must be in moles
 T must be in Kelvin
Combined Gas Law Problems
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In a thermonuclear device, the pressure of 0.050 liters of gas within
the bomb casing reaches 4.0 x 106 atm. When the bomb casing is
destroyed by the explosion, the gas is released into the atmosphere
where it reaches a pressure of 1.00 atm. What is the volume of the
gas after the explosion?
Combined Gas Law Problems (cont)
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The temperature inside my refrigerator is about 4 °C. If I place a
balloon in my fridge that initially has a temperature of 22 °C and a
volume of 0.5 liters, what will be the volume of the balloon when it is
fully cooled by my refrigerator?
Combined Gas Law Problems (cont)
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A gas that has a volume of 28 liters, a temperature of 45 °C, and an
unknown pressure has its volume increased to 34 liters and its
temperature decreased to 35 °C. If I measure the pressure after the
change to be 2.0 atm, what was the original pressure of the gas?
Combined Gas Law Problems (cont)
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If I have 2.9 L of gas at a pressure of 5 atm and a temperature of
50 °C, what will be the temperature of the gas if I decrease the
volume of the gas to 2.4 L and decrease the pressure to 3 atm?
Boyle’s Law
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Discovered in 1662
Determines the relationship between pressure and
volume of a gas
States: For a fixed amount of a gas at a constant
temperature, the volume of a gas varies inversely
with its pressure
Boils down to
 P1
V1  P2 V2
Charles’s Law
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Discovered in 1787
Determined the relationship
between volume and temperature
Temperature must be in Kelvin (K)
States: The volume of a fixed
amount of gas at a constant
pressure is directly proportional to
its Kelvin temperature.
Boils down to:

V1/T1 = V2/T2
Gay-Lussac’s Law
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Discovered in 1802
Determined the relationship between pressure and
temperature
Temperature must be in Kelvin
States: The pressure and Kelvin temperature of a gas
are directly proportional, provided that the volume
remains constant.
Boils down to:
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P1/T1 = P2/T2
Avogadro’s Law
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Proposed in 1811
Determined the relationship between the amount of gas
(number of molecules) and the volume
States: At a fixed temperature and pressure, the volume
of a gas is directly proportional to the amount of gas
(that is, to the number of moles of gas, n, or to the
number of molecules of gas).
At STP, one mole of a gas = _____________
Boils down to
V1/n1 = V2/n2
Using Avogadro’s Law
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What is the mass in kg of 4.55 x 103 L of methane gas (CH4) at STP?
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If 125 mg of Ar(g) is added to a 505 mL sample of Ar(g) at STP, what
volume will the sample occupy when the conditions of STP are restored?
Diffusion and Effusion
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Diffusion- mixing of
two gases together
Effusion- Rate at
which gas molecules
escape from a
container with a small
opening
Graham’s Law
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The rate of effusion and diffusion is inversely
proportional to the square root of the molar mass of
the molecules.
Gases with molecules of lower molar mass have higher
velocities and therefore diffuse or effuse faster
RateA
RateB
=
 MassB
 MassA
RateA = rate of diffusion or effusion for gas A
 RateB = rate of diffusion or effusion for gas B
 MassA = molar mass of gas A
 MassB = molar mass of gas B
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Using Graham’s Law
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A certain gas effuses 4 times as fast as oxygen gas. What is
the molar mass of the unknown gas?
A sample of N2 effuses through a hole in 38 seconds. What
must be the molecular weight of gas that effuses in 55 seconds
under identical conditions?