section 3.5—gas behavior how does the behavior of gases affect airbags?
TRANSCRIPT
Section 3.5—Gas Behavior
How does the behavior of gases affect airbags?
What is pressure?
Pressure – Force of gas particles running into a surface
As number of molecules increases, there are more molecules to collide with the wall
Collisions between molecules and the wall increase
Pressure increases
If pressure is molecular collisions with the container…
As # of molecules increases, pressure increases
Pressure and Number of Molecules
Pressure and Volume
As volume increases, molecules can travel farther before hitting the wall
Collisions between molecules and the wall decrease
Pressure decreases
If pressure is molecular collisions with the container…
As volume increases, pressure decreases
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
Pressure increases
Pressure and Temperature
As temperature increases, molecular motion increases
Collisions between molecules and the wall increase
If temperature is related to molecular motion…and pressure is molecular collisions with the container…
As temperature increases, pressure increases
Pressure Inside and Outside a Container
What is Atmospheric Pressure?
Atmospheric Pressure – Pressure due to the layers of air in the atmosphere.
Less layers of airLower atmospheric pressure
Climb in altitude
As altitude increases, atmospheric pressure decreases.
Pressure In Versus Out
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.
A container will expand or contract until the pressure inside = atmospheric pressure outside
The internal pressure is higher than the external pressure.
The bag will expand in order to reduce the internal pressure.
The internal pressure is from low altitude (high presser)
The external pressure is high altitude (low pressure).
Higher pressure
Lowerpressure
Lower pressure
CanExplodes!
When Expansion Isn’t Possible
Example: An aerosol can is left in a car trunk in the summer. What happens?
Rigid containers cannot expand
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.
The temperature inside the can begins to rise.
As temperature increases, pressure increases.
Higher pressure
Lowerpressure
Kinetic Molecular Theory
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
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Assumptions of the KMT
All gases are made of atoms or molecules
Gas particles are in constant, rapid, random motion
The temperature of a gas is proportional to the average kinetic energy of the particles
Gas particles are not attracted nor repelled from one another
All gas particle collisions are perfectly elastic (no kinetic energy is lost to other forms)
The volume of gas particles is so small compared to the space between the particles, that the volume of the particle itself is insignificant
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Real Gases
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
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 have attractions and repulsions towards one another
Gas particles do take up space—thereby reducing the space available for other particles to be
Effusion & Diffusion
Effusion
Effusion –gas escapes from a tiny hole in the container
Effusion is why balloons deflate over time!
Diffusion
Diffusion –gas moves across a space
Diffusion is the reason we can smell perfume across the room
Effusion, Diffusion & Particle Mass
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
How are particle size (mass) and these concepts related?
As mass of the particles increases, rate of effusion and diffusion is lowered.
Rate of Diffusion & Particle Mass
Watch as larger particles take longer to get to your nose