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

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

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

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 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

Pressure Inside and Outside a Container

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.

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.

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.

Kinetic Molecular Theory What is the 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

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

Real Gases What are 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 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

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 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.

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