1. Mr. Matthew Totaro Legacy High School Regular Chemistry
Properties of Gases
Mr. Matthew Totaro
Legacy High School
Regular Chemistry

2. Gases

3. Properties of Gases Expand to completely fill their container.
Take the shape of their container.
Low density.
Much less than solid or liquid state.
Compressible.
Mixtures of gases are always homogeneous.
Fluid.

4. Properties—Indefinite Shape and Indefinite Volume
Because the gas
molecules have
enough kinetic
energy to overcome
attractions, they
keep moving around
and spreading out
until they fill the
container.
As a result, gases
take the shape and
the volume of the
container they
are in.

5. Properties—Compressibility
Because there is a lot of unoccupied space in the structure
of a gas, the gas molecules can be squeezed closer together.

6. Gas Properties Explained— Low Density
Because there is a lot of unoccupied space in the structure of a gas, gases do not have a lot of mass in a given volume, the result is that they have low density.

7. The Structure of a Gas
Gases are composed of particles that are flying around very fast in their container(s).
They move in straight lines until they encounter either the container wall or another particle, then they bounce off.
If you were able to take a snapshot of the particles in a gas, you would find that there is a lot of empty space in there.

8. Kinetic Molecular Theory
The particles of the gas (either atoms or molecules) are constantly moving.
The attraction between particles is negligible.
When the moving particles hit another particle or the container, they do not stick, but they bounce off and continue moving in another direction.
Like billiard balls.

10. Kinetic Molecular Theory of Gases
There is a lot of empty space between the particles in a gas.
Compared to the size of the particles.
The average kinetic energy of the particles is directly proportional to the Kelvin temperature.
As you raise the temperature of the gas, the average speed of the particles increases.
But don’t be fooled into thinking all the particles are moving at the same speed!!

11. Kinetic Molecular Theory

12. Pressure of a Gas

13. Gas Particles Pushing Gas molecules are constantly in motion.
As they move and strike a surface, they push on that surface.
Push = force.
If we could measure the total amount of force exerted by gas molecules hitting the entire surface at any one instant, we would know the pressure the gas is exerting.
Pressure = force per unit area.

14. The Effect of Gas Pressure
The pressure exerted by a gas can cause some amazing and startling effects.
Whenever there is a pressure difference, a gas will flow from area of high pressure to low pressure.
The bigger the difference in pressure, the stronger the flow of the gas.
If there is something in the gas’ path, the gas will try to push it along as the gas flows.

15. Which Way Would Air Flow?
Two filled balloons are connected with a long pipe. One of the balloons is plunged down into the water. Which way will the air flow? Will air flow from the lower balloon toward the top balloon; or will it flow from the top balloon to the bottom one? 15

16. Soda Straws and Gas Pressure
The pressure of the air inside the straw is the same as the pressure
of the air outside
the straw—so
liquid levels are
the same on both
sides.
The pressure of the
air inside the straw is lower than the pressure
of the air outside
the straw—so
liquid is pushed
up the straw by
the outside air.

17. The Pressure of a Gas
Pressure is the result of the constant movement of the gas molecules and their collisions with the surfaces around them.
The pressure of a gas depends on several factors:
Number of gas particles in a given volume.
Volume of the container.
Average speed of the gas particles.

18. Density and Pressure
When more molecules are added, more molecules hit the container at any one instant, resulting in higher pressure.
Also higher density.

19. Gas Pressure

20. Air Pressure
The atmosphere exerts a pressure on everything it contacts.
On average 14.7 psi.
The atmosphere goes up about 370 miles, but 80% is in the first 10 miles from Earth’s surface.
This is the same pressure that a column of water would exert if it were about 10.3 m high.

21. Atmospheric Pressure

22. Measuring Air Pressure
Use a barometer.
Column of mercury supported by air pressure.
Force of the air on the surface of the mercury balanced by the pull of gravity on the column of mercury.
gravity

23. Atmospheric Pressure and Altitude
The higher up in the atmosphere you go, the lower the atmospheric pressure is around you.
At the surface, the atmospheric pressure is 14.7 psi, but at 10,000 ft it is only 10.0 psi.
Rapid changes in atmospheric pressure may cause your ears to “pop” due to an imbalance in pressure on either side of your ear drum.

24. Effect of Air Pressure
14,000 Feet ,000 Feet 1,000 Feet

25. Pressure Imbalance in the Ear
If there is a difference
in pressure across
the eardrum membrane,
the membrane will be
pushed out—what we
commonly call a
“popped eardrum.”

26. Common Units of Pressure
Average air pressure at sea level
Pascal (Pa)
101,325
Kilopascal (kPa)
Atmosphere (atm)
1 (exactly)
Millimeters of mercury (mmHg)
760 (exactly)
Inches of mercury (inHg)
29.92
Torr (torr)
Pounds per square inch (psi, lbs./in2)
14.7

27. Practice—Convert 45.5 psi into kPa, Continued
Given:
Find:
45.5 psi
kPa
Concept Plan:
Relationships:
1 atm = 14.7 psi, 1 atm = kPa
psi
atm
kPa
Solution:
Check:
Since kPa are smaller than psi, the answer makes sense.