1. Tests…..50% …….30% ???
Let’s vote

2. Kinetic Theory of Gases
CH 13 and CH 14

3. Postulate #1
Particles in a gas are small, hard spheres with insignificant volume
Particles are very far apart
Lots of empty space between the particles
No attraction/repulsion between the particles

4. Postulate #2 Particles in a gas are in constant, random motion
Motion is fast
“Fill” containers regardless of shape
Uncontained gas can spread out into space without limit
Particles travel in straight lines until they collide with something
Estimates put speed of Oxygen molecules at 20 degrees Celsius at 117km/hr (~72 mi/hr)
Odor from pizza would reach Mexico City from Washington DC in 115 minutes!
Does that really happen?
NO! molecules run into stuff and bounce around…rarely go in a straight line for long

5. Postulate #3
All collisions between particles in a gas are perfectly elastic
KE is transferred without loss from one particle to another
Total KE remains constant (really???)

6. Rules for discussing gases
Temperature
(T)
Pressure
(P)
Volume
(V)
# particles
(n)
Must use Kelvin
atm (atmospheres)
kPa (kilopascals)
mmHg (mm mercury
L (liters)
mL (milliLiters)
in3 (inches cubed)
cm3
Need to know if the number of molecules in a container is constant or not
K = C + 273
1 atm =
101.3 kpa =
760 mmHg
1 cm3 = 1 mL
Cannot use Celsius or Fahrenheit
Sometimes see psi (pounds per square inch)

7. Why Worry about these variables?
Pressure is a measure of how many times gas particles are hitting the sides of the container
More hits = more pressure
Increasing temperature = increase in KE
Molecules are moving faster and hit the sides more often
Results in an increase in pressure
Changing the volume will affect pressure
Smaller container with same number of molecules = more pressure
Larger container with same n = less pressure
Changing the number of molecules will affect pressure as well
Which of these are variables are changing and which are constant must always be specified.

8. Homework
P417 #1-6
Due tomorrow