1. Northwestern High School
Lesson Gases
Chemistry 1 Honors
Dr. J. Venables
Northwestern High School

2. Behavior of Gases
Kinetic Molecular Theory. Particles in motion have kinetic energy.
Gas particles are in constant random motion.
Particles collide with other particles or with the walls of the container.
Collisions between gas particles are elastic: no energy is lost.
All gases have the same average kinetic energy at a given temperature.
Gas particles are much smaller than the distances between them.

3. Properties of Gases Explained by Kinetic Molecular Theory
Constant motion of gas particles mean gases expand to fill entire container.
Low density because gas particles get as far apart from each other as possible.
Gases are thousands times less dense than other states of matter (solids and liquids).
Gases can be compressed into smaller volumes. Gas becomes more dense.

4. Compression/Expansion
At given temperature, average kinetic energy of particles remains constant.
Gases compressed. Density increases. Pressure increases. Volume Decreases.
Gases expanded. Density decreases. Pressure decreases. Volume increases.

5. Gas Pressure Pressure is force per unit area. N/m2 = 1 Pascal
Gas particles exert pressure on walls of container.
Air molecules in earth’s atmosphere exert pressure in all directions.
Barometer measures air pressure.

6. Measuring other Gases Manometer measures air pressure of enclosed gas.
Before gas is released into U-Tube, the mercury is at the same height in each arm.
After gas is in U-Tube, the heights in the two arms are no longer equal.

7. Units of Gas Pressure

8. Units of Gas Pressure
1 atmosphere = 760 mm Hg (torr) = kPa = 101,325 Pa = 14.7 psi
Standard Pressure = 1 atmosphere.
EXAMPLES:
What is 447 torr in kPa? In atm? In psi?
What is 134 kPa in mm Hg? In atm?

9. Pressure is linked to Behavior of Particles.
When pump handle is pulled up, the pressure in the pump equals atmospheric.
If the pump piston is pushed down, the air particles are squeezed into a smaller space, and the pressure increases because the frequency of collisions with the inside wall have increased.