Kinetic-Molecular Theory• Describes the behavior of an “ideal” gas in

terms of particle size, motion, and energy based on 5 assumptions…

Gases

1. Do not attract or repel

2. Particles are much smaller than the distances between them

3. Particles are in constant, random motion

4. No kinetic energy is lost during collisions with other particles or walls of container

5. All gases have the same average KE at a given temperature

Properties of Gases

• Low density

• Compression & Expansion

• Diffusion & Effusion

STP

• One mole of any gas will occupy a volume of 22.4 L at STP

• Standard Temperature and Pressure – 0° C and 1 atmosphere

Pressure• Force per unit area

• How do gases exert pressure?

• http://phet.colorado.edu/en/simulation/gas-properties

Air Pressure• Torricelli

• Barometer – used to measure atmospheric pressure

Units of Pressure

• 1 atmosphere

• 101.3 kPa (Pa = Pascal)

• 760 mm Hg

• 760 torr

Boyle’s Law

Pressure and Volume

• Inversely proportional

• If P increases, then V decreases

• P1V1 = P2V2

How to solve

• Make sure all units are the same for both variables

• 1 atm = 101.3 kPa = 760 mm Hg = 760 torr

• Match the units of volume and pressure correctly.

Practice

• A balloon contains 30.0 L of helium at 103 kPa. What is the volume of the balloon where the pressure is 250 kPa?

• P1V1 = P2V2

• (103 kPa) (30.0 L) = (250 kPa) V2

• 12.4 L

• 12 L

• A gas has a volume of 2.50 L when the pressure is 1.0 atmosphere. If the pressure changes to 175 kPa, what is the new volume?

Charles’s Law

Temperature and Volume

• Directly proportional

• If one increases, so does the other!

• Celsius to Kelvin add 273

V1 = V2

T1 T2

Temperature must be in K

Practice• A balloon inflated in a 24°C room, has a volume

of 4.00 L. The balloon is then placed in a room of 58°C . What is the new volume?

Gay-Lussac’s Law

Pressure and Temperature

• Directly proportional

• P1 = P2

T1 T2

Remember to match up units correctly!

Practice

• The gas in an aerosol can is at a pressure of 103 kPa at 25 ºC. If the can is thrown into a fire, what will the pressure be if the temperature reaches 923 ºC?