Unit 6

Kinetic Theory of Gases

Kinetic Theory

• 3 Parts to Kinetic Theory– All particles are in constant random motion

Kinetic Theory

• 3 Parts to Kinetic Theory– All particles are in constant random motion– The motion of one particle is unaffected by the

motion of other particles unless they collide.

Kinetic Theory

• 3 Parts to Kinetic Theory– All particles are in constant random motion– The motion of one particle is unaffected by the

motion of other particles unless they collide.– Forces of attraction among particles in a gas

can be ignored under ordinary conditions.

Kinetic Theory

The molecules move in straight lines and at constant velocity

They only change directions or speed when they collide with other molecules or the sides of the container

Boyle’s Law• As the volume of a gas decreases

(Squeezing), the pressure increases.

• The volume of gas is inversely proportional to the pressure applied.

• Temperature and number of particles are held constant.

• P1V1 = P2V2

Charles’ Law• As the temperature of a gas increases, the

volume increases.

• The volume of a gas is directly proportional to the Kelvin temperature.

• Pressure and number of particles are held constant.

• V1/T1 = V2/T2

Hot Air Balloons work on Charles Law

Hot Air Balloons work on Charles Law

Try It At Home!• Seal an empty water bottle • Throw into the freezer.

• Wait 20 minutes

Try It At Home!• Seal an empty water bottle • Throw into the freezer.

• Check it out after it gets cold!

• Charles Law in effect

Why do you always launch balloons early in the morning?

Why do you always launch balloons early in the morning?

Early morning is cooler, so the temperature difference between the air in the balloon and the outside is greater.

Once up high, the air is cooler and you can stay up for a long time.

Guy-Lussacs’ Law

• Guy-Lussacs’ Law. The number of particles of the substance are held constant.

• P1/T1 = P2/T2

Why is this a problem?

The heat will increase the pressure in the tank until it explodes

Try It At Home!• Seal an empty water bottle

on a high mountain road.• Drive down to sea level

Try It At Home!• Seal an empty water bottle

on a mountain road.• Check it out at sea level!

• Guy-Lussac’s Law

Combined Gas Law• Combination of Boyle’s and Charles’

Law. The number of particles of the substance are held constant.

• P1V1/T1 = P2V2/T2

Why are weather balloons not filled completely at launch?

Combined Gas Law

Ground:

T = 293 KP = 1 AtmV = 100 L

5,000 m:

T = 263 KP = 0.5 AtmV = ?

16,000 m

T = 213 KP = 0.1 AtmV = ?

P1V1/T1 = P2V2/T2

Combined Gas Law

Ground:

T = 293 KP = 1 AtmV = 100 L

5,000 m:

T = 263 KP = 0.5 AtmV = ?

16,000 m

T = 213 KP = 0.1 AtmV = ?

P1V1/T1 = P2V2/T2

1.0atm*100L/293K = 0.5atm*V2/263K

Combined Gas Law

Ground:

T = 293 KP = 1 AtmV = 100 L

5,000 m:

T = 263 KP = 0.5 AtmV = 179 L

16,000 m

T = 213 KP = 0.1 AtmV = ?

P1V1/T1 = P2V2/T2

1.0atm*100L/293K = 0.5atm*V2/263KV2 = 179 L

Combined Gas Law

Ground:

T = 293 KP = 1 AtmV = 100 L

5,000 m:

T = 263 KP = 0.5 AtmV = 179 L

16,000 m

T = 203 KP = 0.1 AtmV = ?

P1V1/T1 = P2V2/T2

1.0atm*100L/293K = 0.1atm*V2/203K

Combined Gas Law

Ground:

T = 293 KP = 1 AtmV = 100 L

5,000 m:

T = 263 KP = 0.5 AtmV = 179 L

16,000 m

T = 203 KP = 0.1 AtmV = 693 L

P1V1/T1 = P2V2/T2

1.0atm*100L/293K = 0.1atm*V2/203KV2 = 693 L

Why are weather balloons not filled completely at launch?

Why are weather balloons not filled completely at launch?

The Atmosphere is much thinner, so the balloon expands

Try It At Home!• Seal an empty water bottle

on a mountain road.• Check it out at sea level!

• Guy-Lussac’s Law