1. Section 3.5—Gas Behavior
How does the behavior of gases affect airbags?

2. What is pressure?
Pressure – Force of gas particles running into a surface

3. Pressure and Number of Molecules
If pressure is molecular collisions with the container…
As number of molecules increases, there are more molecules to collide with the wall
Collisions between molecules and the wall increase
Pressure increases
As # of molecules increases, pressure increases

4. Pressure and Volume
If pressure is molecular collisions with the container…
As volume increases, molecules can travel farther before hitting the wall
Collisions between molecules and the wall decrease
Pressure decreases
As volume increases, pressure decreases

5. What is “Temperature”?
Temperature – proportional to the average kinetic energy of the molecules
Energy due to motion
(Related to how fast the molecules are moving)
As temperature increases
Molecular motion increases

6. Pressure and Temperature
If temperature is related to molecular motion…
and pressure is molecular collisions with the container…
Pressure increases
As temperature increases, molecular motion increases
Collisions between molecules and the wall increase
As temperature increases, pressure increases

7. Pressure Inside and Outside a Container

8. What is Atmospheric Pressure?
Atmospheric Pressure – Pressure due to the layers of air in the atmosphere.
Climb in altitude
Less layers of air
Lower atmospheric pressure
As altitude increases, atmospheric pressure decreases.

9. Pressure In Versus Out
A container will expand or contract until the pressure inside = atmospheric pressure outside
Example:
A bag of chips is bagged at sea level. What happens if the bag is then brought up to the top of a mountain.
The internal pressure is from low altitude (high presser)
The external pressure is high altitude (low pressure).
Lower
pressure
Higher
pressure
Lower
pressure
The internal pressure is higher than the external pressure.
The bag will expand in order to reduce the internal pressure.

10. When Expansion Isn’t Possible
Rigid containers cannot expand
Example:
An aerosol can is left in a car trunk in the summer. What happens?
The temperature inside the can begins to rise.
As temperature increases, pressure increases.
Lower
pressure
Can
Explodes!
Higher
pressure
The internal pressure is higher than the external pressure.
The can is rigid—it cannot expand, it explodes!
Soft containers or “movable pistons” can expand and contract.
Rigid containers cannot.

11. Kinetic Molecular Theory
What is the Kinetic Molecular Theory?

12. Definition
Theory – An attempt to explain why or how behavior or properties are as they are. Based on empirical evidence
Kinetic Molecular Theory (KMT) – An attempt to explain gas behavior based upon the motion of molecules

13. Assumptions of the KMT 1
All gases are made of atoms or molecules 2
Gas particles are in constant, rapid, random motion
The temperature of a gas is proportional to the average kinetic energy of the particles 3
Gas particles are not attracted nor repelled from one another 4
All gas particle collisions are perfectly elastic (no kinetic energy is lost to other forms) 5
The volume of gas particles is so small compared to the space between the particles, that the volume of the particle itself is insignificant 6

14. Real Gases
What are real gases?

15. What is a “real gas”?
Real Gas – 2 of the assumptions of the Kinetic Molecular Theory are not valid
Gas particles are not attracted nor repelled from one another
Gas particles do have attractions and repulsions towards one another
The volume of gas particles is so small compared to the space between the particles, that the volume of the particle itself is insignificant
Gas particles do take up space—thereby reducing the space available for other particles to be

16. Effusion & Diffusion

17. Effusion Effusion –gas escapes from a tiny hole in the container
Effusion is why balloons deflate over time!

18. Diffusion Diffusion –gas moves across a space
Diffusion is the reason we can smell perfume across the room

19. Effusion, Diffusion & Particle Mass
How are particle size (mass) and these concepts related?
As particle size (mass) increases, the particles move slower
it takes them more time to find the hole or to go across the room
Rate of effusion and diffusion is lower
As mass of the particles increases, rate of effusion and diffusion is lowered.

20. Rate of Diffusion & Particle Mass
Watch as larger particles take longer to get to your nose