1. Gases
Describing Gases

2. Review of Kinetic Theory
Particles in an ideal gas…
gases are hard, small, spherical particles
don’t attract or repel each other.
are in constant, random, straight-line motion.
indefinite shape and volume.
have “perfectly” elastic collisions.

3. Variables that describe a gas
Units
Pressure (P) –
kPa, mm Hg, atm, torr
L , mL , cm3
Volume (V) –
°C , K
(convert to Kelvin)
K = °C + 273
Temp (T) –
Mole (n) -
mol

4. Gas Pressure - collision of gas molecules with the walls of the container
Atmospheric Pressure- collision of air molecules with objects

5. Which shoes create the most pressure?
Which create the least? Why?

6. Gas Pressure -- 3 ways to measure pressure:
atm (atmosphere)
mm Hg
kPa (kilopascals)
1 atm = 760 mm Hg = kPa
U-tube Manometer
How can we make these into conversion factors?

7. Atmospheric pressure is measured with a barometer.
Increase altitude – decrease pressure
Ex. Mt. Everest – atmospheric pressure is 253 mm Hg
Vacuum- empty space with no particles and no pressure Ex: space

8. Gases
Kelvin Temperature Scale is directly proportional to the average kinetic energy, so Temperature is a description of the movement of particles (not how hot or cold it is)

9. Standard Temperature and Pressure
STP
Standard Temperature and Pressure
Standard pressure – 1 atm, 760 mm Hg, or kPa
Standard temp. – 0° Celsius or 273 Kelvin