Unit 23
Gases
•Five Premises of Kinetic Molecular Theory (6.5)
The Kinetic-Molecular Theory of Gases (6.5)
•Our understanding of gases is based on a model called the kinetic-molecular
theory of gases. The model is based on five postulates and explains well the
pressure-volume-temperature behavior observed for gases. The five postulates
are:
•Particles of a gas (could be molecules or individual atoms) are in constant rapid motion and move in
straight lines.
•Particles of a gas are tiny compared with the distances between them.
•Particles of a gas are very far apart and thus the intermolecular forces are not important – there is
little attraction or repulsion between the particles of a gas.
•Particles of a gas collide with one another and the energy is conserved in every collision.
•Temperature is a measure of the average kinetic energy (energy of motion) of the gas particles.
•On the ensuing slide you will use an animation to visually look at implications of
these postulates.
Gases at the Particle Level (6.5)
•First, let’s get an appreciation at the
particle level.
•Go to the site:
http://phet.colorado.edu/en/simulation/gas-properties
and click on either the Download button
or the Run Now button. An image similar
to that to the right will appear.
•Use your mouse cursor to raise the pump
handle as high as it will go and then lower
it.
•Watch the particles move around the container for a short while to get an
impression of the particle motion. Do the particles move in straight lines between
collisions? Does the motion appear to be random? Do you see any instances of a
particle being “aware” of another particle other than during collision – do particles
curve at all in their motion?