States of Matter CH 11

The Kinetic-Molecular Theory (KMT)

• Describes the behavior of matter in terms of particles in motion

• Assumptions about gas particles

  • Small particles, little volume, no significant attractive or repulsive forces

  • Elastic collisions - no KE is lost, can be transferred

  • Temperature is a measure of average KE

Gas Behaviors

Low density, compression, expansion, diffusion,

effusion

Low density

fewer particles in same volume as a solid

Compression

large amount of empty space can squeeze into smaller volume

Expansion

random particle motion fills available space

Diffusion

the movement of one material through another

• occurs from high to low concentrations

Effusion

a gas escapes through a tiny opening

Gas Pressure

the force per unit area

Units of pressure

• SI unit - pascal (Pa)

• mm Hg, atm, torr

Sea Level

101.3 kPa at 0 degrees C

Air Pressure

varies with position on Earth

Low altitude

higher pressures greater amount of particles, more gravity

Barometer

used to measure atmospheric pressure

Atmospheric Pressure

varies

“The air is thin” at high altitudes

• Athletes go days before a competition to acclimate

• Baseballs and gold balls travel further

  • less air resistance

Higher altitudes

lower atmosphere pressure

Low altitudes

higher atmosphere pressure

Less pressure = less particles = less O2 to breathe

Remember

Dalton’s Law of Partial Pressure