2.
Gases
How does the KMT explain the behavior of gases?
Kinetic Molecular
Theory Has 3 parts:
1. Particle Size
2. Particle Motion
3. Particle energy
In your groups, describe
the properties of a
gas using these three
Review Physical States of Matter categories.
3. Gases
Kinetic Molecular Theory:
Particle Size
Gases consist of small particles separated by empty space.
The volume of the particle is small compared to the empty space.
Gases have no attractive or repulsive force.
4. Kinetic Molecular Theory
•Particle Motion
•Gas particles travel in constant, random motion.
•Particles move in a straight line until the collide with
another particle, or with the wall of its container.
•Gas particle collisions are elastic.
5. Kinetic Molecular Theory
Particle Energy
The kinetic energy of a gas particle is determined by mass and
speed.
Gas molecules have high kinetic energies.
6. Properties of Gases
Gases can be compressed
Compression is the ability to decrease the volume of a gas.
7. Warm Up
Use the Kinetic Molecular Theory to explain the
following:
Why do gases expand to fill their containers?
Why do gases have a low density?
Why can gases be compressed, but solids and liquids
cannot?
8. How are pressure and volume of a gas related?
Question: What might happen to the gas
in a balloon if you decreased its volume
by squeezing it?
9. How is pressure defined?
Pressure: force exerted per unit area.
Gas molecules exert pressure when they collide with the walls
of their container.
As the number of gas molecules in a container increases,
pressure _______________.
10. Measuring Pressure
SI unit for pressure: pascal
At sea level, the average air pressure is 101.3 kPa
Air pressure is measure in atmospheres (atm)
1 atm = 101.3 kPa
11. Pressure
Evangelista Torricelli, one of the first to discover atmospheric
pressure, once said, "We live submerged at the bottom of an ocean
of the element air." The Earth's gravitational field is pulling on air,
and this pull, or "pressure" of air, is called atmospheric pressure.
Boyle's Law Simulation
12. Boyle’s Law Relates Pressure to Volume
If temperature and amount of gas particles are held constant,
pressure will ___________ when volume decreases.
The farther you are from sea level, atmospheric pressure
decreases.
Why would it be difficult to breathe in the mountains?
Why do Olympic athletes often train at high altitudes?
Why are airplane cabins “pressurized” before take off?
13. Boyle’s Law
P1V1 = P2V2
P1 and V1 represent initial conditions
P2 and V2 represent final conditions
A scuba diver blows a 0.75 L air bubble 10 m under water. As it
rises to the surface, the pressure goes from 2.25 atm to 1.03
atm. What will be the volume of air in the bubble at the
surface?
14. Boyles Law and Breathing
How does Boyle’s Law explain breathing?
As your diaphragm moves downward, the lungs expand.
As your diaphragm moves upward, the lungs shrink in volume.
Why does air enters the lungs when you inhale, and exit the lungs
when you exhale?
When a person is ill with emphysema, parts of the lungs lose their
elasticity and become enlarged. Why does this affect their
breathing?
Why are beginning scuba divers taught to never hold their breath
when they are under water?
15. Warm up
A balloon contains 30 L of
helium gas at sea level. As
the balloon is released in
to the sky, the volume
increases to 42 L of
helium. What is the final
pressure of helium gas?
17. Charles’ Law
Why do breads and muffins rise when baked?
Why is a higher temperature required to bake at higher altitudes?
What happens to a balloon in liquid nitrogen?
What happens to soda that is left in a car on a hot summer day?
Why is laying on an air mattress more comfortable that laying on
the ground?
18. Charles’ Law
V1 = V2
T1 = T2
A helium balloon in a closed car occupies a volume of
2.32 L at 40 degrees celsius. If the car is parked on
a hot day and the temperature inside rises to 75
degrees celsius, what is the new volume of the
balloon, assuming the pressure remains constant?
19. Charles’ Law
V1 = V2
T1 = T2
A helium balloon in a closed car occupies a volume of 2.32 L at 40
degrees celsius. If the car is parked on a hot day and the
temperature inside rises to 75 degrees celsius, what is the new
volume of the balloon, assuming the pressure remains
constant?
2.32 = V2
40 = 75 (2.32)(75) = 40(v2)
4.35 L = V2
21. How are Pressure and Temperature
Related?
Why do chefs use a “pressure cooker”?
22. Combined Gas Law
What is held constant in the combined gas law?
You can derive each Gas Law from the Combined Gas Law.
23. Combined Gas Law
A gas at 110 kPa and 30 degrees C fills a flexible container with
an initial volume of 2.00 L. If the temperature is raised to 80
degrees C and the pressure increases to 440 kPa, what is the
new volume?
24. Combined Gas Law
A gas at 110 kPa and 30 degrees C fills a flexible container with
an initial volume of 2.00 L. If the temperature is raised to 80
degrees C and the pressure increases to 440 kPa, what is the
new volume?
25. Practice
An unopened, cold 2.00-L soda bottle contains 46 mL of gas
confined at a pressure of 1.3 atm at a temperature of 5 degrees
Celsius. If the bottle is taken on a submarine which sinks to a
depth at which the pressure is 1.52 atm and the temperature is
2.09 degrees C, what will be the volume of gas in the bottle?
26. Graphic Organizer
Complete the following graphic organizers:
Effect Effect Effect
Pressure increase
Volume increase
Temperature decreases
Law Boyle’s Charles’s Combined
Formula
What is held
constant?
27. The Ideal Gas Law
How is the amount of gas particles related to pressure,
temperature and volume?
28. Warm Up
Each balloon below contains 1 L of gas. Answer the following:
Are the volumes equal?
Are the number of molecules equal? The moles?
Are the masses equal?
H2 C3H8 He
CH4 N2 CO2
29. Avagadro’s Principle
The KMT assumes that gas particles are far apart.
Therefore, size of a gas particle is negligible
Does size (mass) of a gas molecule determine volume of a gas?
30. Avagadro’s Principle
NO!!!!! 1,000 Krypton gas
particles occupy the same
Avagadro proposed……. volume as
1000 helium gas particles.
(At the same temperature
and pressure of course)
31. Avagadro’s Principle
Equal Volumes of gas at the SAME temperature and
pressure contain equal numbers of particles.
