1. Kinetic Molecular Theory

2. Gases
Gases are one of the most pervasive aspects of our environment on the Earth. We continually exist with constant exposure to gases of all forms.
The steam formed in the air during a hot shower is a gas.
The Helium used to fill a birthday balloon is a gas.
The oxygen in the air is an essential gas for life.

3. Important Characteristics of Gases
1) Gases are highly compressible
An external force compresses the gas sample and decreases its volume, removing the external force allows the gas volume to increase.
2) Gases are thermally expandable
When a gas sample is heated, its volume increases, and when it’s cooled, its volume decreases.
3) Gases have high viscosity
Gases flow much easier than liquids or solids.
4) Most Gases have low densities
Gas densities are on the order of grams per liter whereas liquids and solids are grams per cubic cm, 1000 times greater.
5) Gases are infinitely miscible
Gases mix in any proportion such as in air, a mixture of many gases

4. Substances That Are Gases under Normal Conditions
Substance Formula MM(g/mol)
Helium He
Neon Ne
Argon Ar
Hydrogen H
Nitrogen N
Nitrogen Monoxide NO
Oxygen O
Hydrogen Chloride HCl
Ozone O
Ammonia NH
Methane CH

5. Kinetic Molecular Theory
To fully understand the world around us requires that we have a good understanding of the behavior of gases.
The description of gases and their behavior can be approached from several perspectives.
The Gas Laws are a mathematical interpretation of the behavior of gases.
In addition to understanding the mathematics of gases, a chemist must have an understanding of the conceptual description of gases.

6. Kinetic Molecular Theory: What and WHy
All real gases require their own unique sets of descriptive characteristics.
trying to describe each one of them individually would be a monumental task.
In order to simplify this task, the scientific community has decided to create an imaginary gas, the Ideal Gas, that approximates the behavior of all real gases.
In other words, the Ideal Gas is a substance that does not exist.
The Kinetic Molecular Theory describes that gas.

7. THE KINETIC THEORY OF GASES
Ideal Gases:
Gas consists of large number of particles (atoms or molecules) in random, straight- line motion
Particles make elastic collisions with each other and with walls of container- may transfer energy but no net loss
Particles, on average, separated by distances large compared to their diameters, so their volume is considered negligible
No forces of attraction between particles

8. The Nature of Gases
Three basic assumptions of the kinetic theory as it applies to gases:
1. Gas is composed of particles- usually molecules or atoms
Small, hard spheres
Insignificant volume; relatively far apart from each other
No attraction or repulsion between particles

9. 2. Particles in a gas move rapidly in constant random motion
Move in straight paths, changing direction only when colliding with one another or other objects
Average speed of O2 in air at 20 oC is an amazing 1660 km/h! (1.6km=1mile)

10. Collisions are perfectly elastic- meaning kinetic energy is transferred without loss from one particle to another- the total kinetic energy remains constant

11. Elastic vs. Inelastic Collisions8 3

12. Elastic vs. Inelastic Collisions
POW 8 v1 v2
elastic collision v3 v4 8
inelastic collision

13. What happens to a ball when it drops?
…..but in reality the ball loses height and eventually stops bouncing
Which is converted to potential energy in the ball
The potential energy of the ball
Which is converted into the potential energy of the ball…………..
Which is converted to kinetic energy in the ball
Is converted to kinetic energy in the ball
Why does this happen?

14. 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