Notes on Gases:
A Summary of Chapters 13 & 14
Section 1: Properties of Gases
Section 2: Gas Laws
Section 3: Gas Stoichiometry
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Gas Properties
1)
2)
3)
4)
5)
Kinetic Molecular Theory:
Gases consist of large numbers of
particles that are far apart.
When particles collide, they do not
lose energy.
Gas particles are in continuous, rapid,
random motion.
There are no forces of attraction
between gas particles.
Average temperature of a gas
depends on the temperature.
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More Properties…
Expansion:
-No definite shape or volume.
Gases naturally expand to fill their
containers.
Fluidity:
Gas particles glide past one another
causing them to “flow” like liquids.
(Liquids and gases are FLUIDS.)
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More Properties…
Low Density:
Particles are so far apart compared to
solids and liquids the density is really
low…therefore, gases float!
Compressibility:
Gas particles can be squeezes closer
together (causing the volume to
decrease and the pressure to increase).
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More Properties…
Diffusion:
Natural mixing of gas particles
caused by random motion.
Effusion:
Process of gas particles passing
through a tiny opening.
Ex. – Hole in a bike tire.
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What is Pressure?
Pressure (P) is the force applied over a
surface area. Measured in newtons (N).
P = force
area
Barometers are used to measure atmospheric
pressure. Measured in…
1.
2.
3.
4.
Millimeters of mercury (mm Hg)
Atmospheres (atm)
Torricelli (torr) *invented the barometer*
Pascal (Pa) or kilopascal (kPa)
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Units for Pressure
(All calculations must be in atm!!!)
Atmospheric pressure at sea level:
1 atm = 760 mm Hg
= 760 torr
= 101.3 kPa
Units for Temperature
(All calculations must be in Kelvin!!!)
Converting from Kelvin  Celsius
C = K – 273
Converting from Celsius  Kelvin
K = C + 273
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Standard
Temperature and Pressure
Oftentimes, chemists want to use the same
conditions for several experiments…so a
standard temperature and pressure was
agreed upon.
STP = 0ºC and 1 atm
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The Gas Laws
1.
2.
3.
4.
5.
Boyle’s Law (Pressure-Volume)
Charles’s Law (Temperature-Volume)
Gay-Lussac’s Law (Temperature-Pressure)
Combined Gas Law (P-T-V)
Ideal Gas Law (P-T-V-Moles)
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Boyle’s Law (Pressure-Volume)
P1V1 = P2V2
If pressure increases, volume will ________.
If pressure decreases, volume will ________.
This relationship is ________.
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Boyle’s Law (Pressure-Volume)
P1V1 = P2V2
If pressure increases, volume will decrease.
If pressure decreases, volume will increase.
This relationship is inverse.
Lungs Video
Marshmallows Video
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Charles’s Law
(Temperature-Volume)
V1 = V2
T1 T2
If temperature increases, volume will _______.
If temperature decreases, volume will _______.
This relationship is ________.
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Charles’s Law
(Temperature-Volume)
V1 = V 2
T1 T2
If temperature increases, volume will increase.
If temperature decreases, volume will decrease.
This relationship is direct.
Liquid Nitrogen + Balloon
55-Gallon Can
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Gay-Lussac’s Law
(Temperature-Pressure)
P1 = P2
T1 T2
If temperature increases, pressure will ______.
If temperature decreases, pressure will ______.
This relationship is ________.
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Gay-Lussac’s Law
(Temperature-Pressure)
P1 = P 2
T1 T 2
If temperature increases, pressure will increase.
If temperature decreases, pressure will decrease.
This relationship is direct.
Fountain
Egg + Bottle
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Wouldn’t it be easier if we only had one formula?
COMBINED GAS LAW
P1 V1 = P2 V2
T1
T2
If one of these variables is constant, block it out and
use the equation that is left.
If temperature is constant (no T) = Boyle’s Law
If pressure is constant (no P) = Charles’s Law
If volume is constant (no V) = Gay-Lussac’s Law
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Summary of Formulas
Boyle’s Law : P1V1 = P2V2
Charles’s Law : V1 = V2
T1 T2
Gay-Lussac’s Law : P1 = P2
T1 T2
Combined Gas Law :
P1 V1 = P2 V2
T1
T2
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PRACTICE – 1 of 4
COMBINED GAS LAW
P1 V1 = P2 V2
T1
T2
Q1: A sample of Neon gas occupies a volume
of 752mL at 25ºC. What volume will the
gas occupy at 50ºC if the pressure remains
constant? What law will we use?
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PRACTICE – 2 of 4
COMBINED GAS LAW
P1 V1 = P2 V2
T1
T2
Q2: A sample of oxygen gas has a volume of
150.mL when its pressure is 0.947atm. What
will the volume of the gas be if the pressure
increases to 0.987atm? (Temperature remains
constant.) What law will we use?
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PRACTICE – 3 of 4
COMBINED GAS LAW
P1 V1 = P2 V2
T1
T2
Q3: The gas in an aerosol can is at a pressure of
3.00atm at 25ºC. Directions on the can warn the
user not to keep the can in a place when the
temperature exceeds 52ºC. What would the
pressure in the can be at 52ºC? (Assume volume
remains constant.) What law will we use?
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PRACTICE – 4 of 4
COMBINED GAS LAW
P1 V1 = P2 V2
T1
T2
Q4: A helium-filled balloon has a volume of
50.0L at 25ºC and 1.03atm. What volume
will it have at 0.855atm and 10ºC? What
law will we use?
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The Ideal Gas Law
A law relates pressure, volume,
temperature, and the number of
moles of a gas.
PV = nRT
P = pressure (in atm)
V = volume (in L)
n = number of moles (in moles)
R = Ideal Gas Constant (0.0821 always)
T = temperature (in Kelvin)
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PRACTICE – 1 of 3
Ideal Gas Law
PV = nRT
Q1: What is the pressure (in atm) exerted by a
0.500 mol sample of nitrogen gas in a
10.0L container at 298K?
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PRACTICE – 2 of 3
Ideal Gas Law
PV = nRT
Q2: What is the volume (in liters) of 0.250
moles of oxygen gas at 20.0ºC and 0.974
atm of pressure?
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PRACTICE – 3 of 3
Ideal Gas Law
PV = nRT
Q3: How many moles of chlorine (Cl2) is
contained in a 10.0L tank at 27ºC and
3.50atm of pressure?
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Final Summary of Formulas
Boyle’s Law : P1V1 = P2V2
Charles’s Law : V1 = V2
T1 T2
Gay-Lussac’s Law : P1 = P2
T1 T2
Combined Gas Law :
P1 V1 = P2 V2
T1
T2
Ideal Gas Law : PV = nRT
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FINAL SECTION: Gas Stoichiometry
Same rules as Reaction Stoichiometry…
We are simply adding one value –
standard molar volume.
The volume occupied by one mole of gas at STP
(Standard Temperature and Pressure).
standard molar volume = 22.4 L/mol of gas.
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PRACTICE – 1 of 4
Gas Stoichiometry
Q1: A chemical reaction produces 0.0680 mol
of oxygen gas. What volume (in liters) is
occupied by the gas at STP?
(Remember the value 22.4L/mol.)
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PRACTICE – 2 of 4
Gas Stoichiometry
Q2: A chemical reaction produced 98.0 mL of
sulfur dioxide gas (SO2) at STP. What was
the mass in grams of the gas produced?
(Remember the value 22.4L/mol.)
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PRACTICE – 3 of 4
Gas Stoichiometry
CaCO3  CaO + CO2
Q3: How many grams of calcium carbonate
must be decomposed to produce 5.00L of
carbon dioxide gas at STP?
(Use PV=nRT)
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PRACTICE – 4 of 4
Gas Stoichiometry
WO3 (s) + 3H2 (g)  W(s) + H2O(l)
Q4: How many liters of hydrogen gas at 35ºC
and 0.980 atm are needed to react
completely with 875 g of tungsten oxide?
(PV=nRT)
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YouTube Videos – GAS HELP
1. Gas Stoichiometry #1
2. Gas Stoichiometry #2
3. Molar Volume Explanation
4. How to Collect a Gas Experimentally
5. Ideal Gas Law Example
6. Diffusion of Gas Demos
7. Effusion of Heavy Gas (Sulfur hexafluoride)
8. Effusion of Light Gas (Hydrogen)
9. Kinetic Molecular Theory of Gases
10. Properties of Gases
33
Review Topics for the Test
I.
Properties of Gases
a) Kinetic Molecular Theory (5 parts)
b) Fluidity, Expansion
c) Compressibility, Density
d) Effusion/Diffusion
e) Units for Temperature and Pressure
f) STP
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Review Topics for the Test
II. Gas Laws
Boyle’s Law : P1V1 = P2V2
Charles’s Law : V1 = V2
T1 T2
Gay-Lussac’s Law : P1 = P2
T1 T2
Combined Gas Law :
P1 V1 = P2 V2
T1
T2
Ideal Gas Law : PV = nRT
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Review Topics for the Test
III. Gas Stoichiometry
• Converting from moles  Liters
• Converting from Liters  moles
• Converting from grams  Liters
• Converting from Liters  grams
• Using a balanced equation to predict
grams or Liters by using PV=nRT
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Remember:
- Scientific Calculator
- Pencil
- Scratch paper
- 3x5 Note Card (front/back)
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