Chemistry 112

1
Chemistry 112

• Chapter 12
• Gases

2
The Atmosphere

• The Universe is made out of gas for the most part
  (H2).
• The atmosphere is the thin layer of gases that
  surround the earth.
• Air is composed of a mixture of gases
• 78 Nitrogen, N2
• 21 Oxygen, O2
• 1 Argon, Ar
• gt365 ppm carbon dioxide, CO2 (only 296 ppm in
  1900!)
• 0-4 water, H2O

Dry Air
3
Physical Properties of Gases

• No definite shape or volume
• expand to fill container, take shape of
  container.
• Compressible
• increase pressure, decrease volume.
• Low Density
• air at room temperature and pressure 0.00117
  g/cm3.
• Exert uniform pressure on walls of container.
• Mix spontaneously and completely.
• diffusion

4
End of Chapter Problems

• 6, 10, 28, 32, 36, 42, 46, 56, 82, and 90.

5
Kinetic Theory of Gases

• 1. Gas particles move continuously in all
  directions.
• 2. Gas particles are extremely small and
  distances between them are great.
• 3. Gravitational forces between molecules are
  negligible.
• 4. Collisions between gas molecules are elastic
  (no loss of energy in collision).

6
Kinetic Energy

• 5. The average kinetic energy is the same for
  all gases it varies with temperature.
• K. E. ½mv2
• m mass of the gas particle
• v velocity of particle
• When temperature increases velocity of particles
  increases.

7
Pressure

• Pressure is the force exerted per unit area
• Atmospheric Pressure is the force per unit area
  exerted by the earths atmosphere.
• Atmospheric Pressure is measured with a barometer.

8
Pressure Units

• mm of mercury (mm Hg)
• 1 mm Hg 1 torr
• 760 mm Hg 1 atm 760 torr 14.7 psi
• 1 atm is 1 atmosphere of pressure, sometimes
  called standard pressure.
• 1 Pascal, Pa, is the SI unit of pressure
• 1 Pa 1 N/m2 9.9 x 10-6 atm

9
Boyles Law

• As the pressure of a gas is increased the volume
  decreases at constant temperature
• V ?1/P
• This is an inverse proportion
• PV k
• P1V1 P2V2

10
Boyles Law Graph
11
Relation of Volume and Pressure

• As the container volume decreases at constant
  temperature, the smaller volume has shorter
  distances between gas molecules and the walls, so
  collisions are more frequent. Hence, the pressure
  increases at lower volume.

12
Example

• A space capsule is equipped with a tank of air V
  0.100 m3 and P 100.0 atm. After a space walk,
  the cabin is refilled with air from the tank.
  What will be the final pressure in the tank if
  the capsule volume is 12.5 m3?