Honors Chemistry
08-01: The Nature of Gases
Kinetic Theory and a Model for Gases
Page 1 of 4
Objectives:

Upon completion of this presentation, you will be able to …

state the Kinetic Theory of Gases.

state the assumptions of the Kinetic Theory of Gases.

apply the assumptions of the Kinetic Theory to ideal and real gases.
Introduction:

Kinetic means __________________ .
o Kinetic energy, KE, is the energy of motion.

The __________________ __________________ is a model of matter where ...
o ... all matter is composed of tiny particles ...
o ... in constant motion.

The kinetic theory applies to __________________ states of matter.

We will apply it first to gases and then extend the theory to liquids and solids.

The kinetic theory describes the behavior of matter in its various states.

There are a series of assumptions we make about matter in order to use the
theory.
o These assumptions help us to understand how to apply the theory to

... gases ...

... liquids ...

... and solids.
Honors Chemistry
08-01: The Nature of Gases
Kinetic Theory and a Model for Gases
Page 2 of 4
First Assumption:

The particles in a gas are considered to be very __________________ , very
__________________ spheres with an insignificant __________________.

This means that the individual gas particles ...
o are atoms or small molecules
o are very far apart in relation to the size of the particles
o have very little attraction or repulsion towards one another
o move independently of each other
Second Assumption:

The motion of the particles in a gas is __________________ , __________________ , and
__________________ .

This means that the individual gas particles ...
o spread out to fill any volume or shape of container
o travel in straight lines until they encounter another particle or
another object
o change direction only after a collision

Experimental measurements of gas molecules show that they move quite
rapidly, even at __________________ __________________..
o O2 molecules have an average speed of 1,700 km/hr (1,060 mph).
o However, they only travel about 70 nm until they encounter another
particle.

This is about 500 times their diameter
Honors Chemistry

08-01: The Nature of Gases
Kinetic Theory and a Model for Gases
Page 3 of 4
Each gas molecule travels in a very crooked path called a __________________
__________________ .
Third Assumption:

All collisions between gas particles are __________________ __________________ .

This means that the individual gas particles ...
o transfer kinetic energy during a collision
o collide without a loss of kinetic energy
o have a total kinetic energy that remains constant
Applications:

We can use these assumptions to understand the behavior of real gases.
o __________________:

Gases are compressible.

This can be explained by the __________________ assumption:

the small size of gas particles

the large distance between gas particles
o __________________ :

Gases expand to fill all available space of a container.

This can be explained by the __________________ assumption:

gas particles move rapidly, constantly, and randomly

this movement will allow the gas particles to move to
the limits of the container
Honors Chemistry
08-01: The Nature of Gases
Kinetic Theory and a Model for Gases
Page 4 of 4
o __________________ :

Gases are by far the least dense of the states of matter.

This can be explained by the __________________ assumption:

the combination of the small size of gas particles and
the large distance between gas particles leads to a
very low density.
Note:

The textbook lists only 3 assumptions of the kinetic theory of matter.

There are, in fact, many more assumptions in a complete treatment of the
kinetic theory.

All of these assumptions help us to better understand the nature of matter in
all of its states.

Some examples of additional assumptions include:
o The number of molecules is so large that statistical treatment can be
applied.
o The average kinetic energy of the gas particles depends only on the
temperature of the system.
o The time during collision of molecule with the container's wall is
negligible as comparable to the time between successive collisions.
o The equations of motion of the molecules are time-reversible.