1. Chapter 13 States of Matter

3. 13.1 The Nature of Gases
Kinetic refers to motion…kinetic energy
The kinetic theory states that tiny particles in all forms of matter are in constant motion

4. Three basic assumptions of the kinetic theory as it applies to gases:
#1 Gas is composed of particles…molecules or atoms
- small, hard spheres
-insignificant volume, far apart from each other
-no attraction or repulsion between particles

5. #2 Particles in a gas move rapidly in constant random motion -move in straight paths, changing direction only when colliding with each other or other objects -average speed of O2 in air at 20° C is 1700km/h

6. #3 Collisions are perfectly elastic
-total kinetic energy remains constant

7. Gas Pressure – the force exerted by a gas per unit surface area of an object
Due to:
1) Force of collisions
2) Number of collisions

8. What if there are no particles?

9. No collisions
No pressure
Vacuum

10. Results from the collisions of air molecules with objects
Atmospheric Pressure
Results from the collisions of air molecules with objects
What happens if you climb to the top of a mountain…or dive deep in the ocean?

11. Measuring Pressure
Evangelista Torricelli created the first barometer
Baro = weight
Meter = measure

12. Barometer Measures atmospheric pressure
Depends on weather and altitude

13. SI unit of pressure, pascal, Pa
At sea level, atmospheric pressure is about kPa, kilopascals
Older units of pressure
Millimeters of mercury (mm Hg)
Atmospheres (atm)

14. Using a mercury barometer…
at sea level, the Hg would rise to a height of 760 mm at 25° C
This is called one standard atmosphere (atm)

15. For gases it is important to relate measured values to standards:
Temperature of 0° C
Pressure of kPa, or 1 atm
Standard Temperature & Pressure STP

16. What happens when a substance is heated?
Some of the energy is stored in the particles…called?
It does not raise the temperature
Remaining energy speeds up the particles, increases average kinetic energy  increasing temperature also

17. The particles in any collection have a wide range of kinetic energies, but most are somewhere in the middle...
So we use the term average kinetic energy

18. An increase in the average kinetic energy of particles causes the temperature to rise
As it cools, particles move more slowly and average K.E. decreases
Will they ever slow down enough to stop moving?

19. The particles would have no kinetic energy because no motion
Absolute zero (0 K or -273° C)

20. The Kelvin temperature of a substance is directly proportional to the average kinetic energy of the particles of the substance