1. Gas and Pressure

2. Review Kinetic Vs. Potential Energy

3. Kinetic Molecular Theory
Explains the behavior of gases
Real gases– do not follow all the assumptions of this theory.
Theoretical, applies to an ideal gas
Gas following all the assumptions of the theory.

4. Kinetic Molecular Theory
Gases are made up of TONS of particles, constantly moving, and spread out.
Gas particles drive straight until they hit/collide with something (ex. Wall, particles).
Small particles, HUGE space for them to roam! Gas volume mainly empty space

5. Kinetic Molecular Theory (cont.)
4) No force of attraction! –gas particles randomly move around
5) When gas particles collide with each other or a container wall, no kinetic energy is lost when they collide.
6) Temperature determines average kinetic energy of gas particles.
-not all gas particles are moving at the same kinetic energy

7. Properties of Gases 1) Expandable 2) Fluid 3) Low Density No shape
No defined volume
Fills whatever container is available to it.
Move quickly and no attraction
2) Fluid
Gases move similar to liquids
No attraction to worry about
3) Low Density
Least dense state of matter for most substances
Due to distance between particles

8. Properties of Gases (cont.)
4) Diffusion
Gas particles mix with each other and disperse
“Spontaneous mixing of gas particles from 2 substances due to random motion” (ex. Perfume)
5) Effusion
Describes gas movement through a small opening. (ex. Tire puncture)
Related to how fast gas particles can move.
6) Compressibility
Gas particles are able to be packed close together.
Decreased volume

9. Pressure “force per unit area on a surface”
Gas particles colliding against container and creating force
Force a gas exerts on its surroundings
Unit = Newton (N)
Amount of pressure dependent on Volume, Temperature, and particle/molecule number.
Ex. Atmospheric pressure

10. How do we measure pressure?
Barometer– atmospheric pressure
Evangelista Torricelli (1600s)
Mercury falls to 760 mm
Air pressure holds 760 mm mercury column.

11. Barometer Vacuum 760 mm Hg 1 atm Pressure
The pressure of the atmosphere at sea level will hold a column of mercury 760 mm Hg.
1 atm = 760 mm Hg
760 mm Hg
1 atm Pressure

12. Pressure Units Common: mmHg (millimeters of Hg)
Measurements done in “atmosphere units”
1 atmosphere of pressure (atm) = (sea level, 0° C)
760 mmHg
760 torr
x 105 Pa
kPa

13. Example 1:
1.75 atm of pressure to mmHg

14. Example 2:
570 torr of pressure to atmospheres.
kPa?

15. Pressure Conversion Practice
The tire pressure for one tire on my car reads atm. Convert this pressure to mmHg.
200 torr kPa
3. The atmosphere supports a column of mercury at 670 mm in height. What is the atmospheric pressure in atm?
15 Pa atm
A weather report gives a current atmospheric pressure reading of mmHg. Express this reading in kilopascals.

16. Homework
Post-Lab Questions
Study for Kinetics Quiz on Tuesday