Kinetic Molecular Theory solids, liquids and gases

science

1. Collisions of Gas Particles

2. Collisions of Gas Particles

3. Kinetic Theory

4. Kinetic Molecular Theory
Postulates of the Kinetic Molecular Theory of Gases
1.Gases consist of tiny particles (atoms or molecules)
2.These particles are so small, compared with the distances between
them, that the volume (size) of the individual particles can be assumed
to be negligible (zero).
3. The particles are in constant random motion, colliding with the walls of
the container. These collisions with the walls cause the pressure exerted
by the gas.
4. The particles are assumed not to attract or to repel each other.
5. The average kinetic energy of the gas particles is directly proportional
to the Kelvin temperature of the gas

5. Kinetic Molecular Theory (KMT)
1.…are so small that they are assumed to have zero volume
2.…are in constant, straight-line motion
3.…experience elastic collisionsin which no energy is lost
4.…have no attractive or repulsiveforces toward each other
5.…have an average kinetic energy (KE)that is proportional
to theabsolute temp. of gas (i.e., Kelvin temp.)
AS TEMP. , KE
explains why gases behave as they do
deals
w
/“ideal” gas particles…

6. Elastic vs. Inelastic Collisions
8
3

7. 8
Elastic vs. Inelastic Collisions
8
v
1
elastic collision
inelastic collision
POW v
2
v
3 v
4

8. 8
Elastic Collision
8
v
1
before
v
2
after

9. Model Gas Behavior
•All collisions must be elastic
•Take one step per beat of the
metronome
•Container
–Class stands outside tape box
•Higher temperature
–Faster beats of metronome
•Decreased volume
–Divide box in half
•More Moles
–More students are inside box
Mark area of container
with tape on ground.
Add only a few
molecules of inertgas
Increase temperature
Decrease volume
Add more gas
Effect of diffusion
Effect of effusion
(opening size)

10. Kinetic Molecular Theory
•Particles in an ideal gas…
–have no volume.
–have elastic collisions.
–are in constant, random, straight-line motion.
–don’t attract or repel each other.
–have an avg. KE directly related to Kelvin temperature.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

11. Molecular Velocities
speed
Fractions of particles
the Maxwell speed distribution
http://antoine.frostburg.edu/chem/senese/101/gases/slides/sld016.htm
molecules sorted by speed
many different molecular speeds

12. Real Gases
•Particles in a REAL gas…
–have their own volume
–attract each other
•Gas behavior is most ideal…
–at low pressures
–at high temperatures
–in nonpolar atoms/molecules
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

13. Characteristics of Gases
Gases expand to fill any container.
–random motion, no attraction
Gases are fluids (like liquids).
–no attraction
Gases have very low densities.
–no volume = lots of empty space
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

14. Characteristics of Gases
•Gases can be compressed.
–no volume = lots of empty space
•Gases undergo diffusion & effusion.
–random motion
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

15. Properties of Gases
V = volumeof the gas (liters, L)
T = temperature(Kelvin, K)
P = pressure(atmospheres, atm)
n = amount(moles, mol)
Gas properties can be modeled using math.
Model depends on:

16. Pressure -Temperature -Volume
Relationship
P T V
Gay-Lussac’s P Ta
Charles V Ta
Boyle’s P
1
V
a
___

17. Pressure -Temperature -Volume
Relationship
P T V
Gay-Lussac’s P Ta
Charles V Ta
Boyle’s P
1
V
a
___
P n V

18. Pressure and Balloons
A
B = pressure exerted ON balloon
A = pressure exerted BY balloon
B
When balloon is being filled:
P
A> P
B
When balloon is filled and tied:
P
A= P
B
When balloon deflates:
P
A< P
B

19. When the balloons are untied,
will the large balloon (A) inflate
the small balloon (B); will they
end up the same size or will the
small balloon inflate the large
balloon?
Why?
Balloon Riddle
A
B
C

20. Kinetic Theory and the Gas Laws
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3
rd
Edition, 1990, page 323 (newer book)
original temperature
original pressure
original volume
increased temperature
increased pressure
original volume
increased temperature
original pressure
increased volume
(a) (b) (c)
10 10 10
10