Kinetic Molecular Theory of Gases

Kinetic-molecular theory is a simple model to explain properties of gases. There are four basic postulates:

animation of translational motion in gasses

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  1. Gases are easy to compress - expected if there is lots of empty space between them.

  2. This explains why gases rapidly fill their containers. We also note that they don't condense out as a liquid or solid if they are left in an insulated container (they don't lose energy as they collide with walls.) Brownian motion is also a consequence of their rapid movement.

  3. Three is a bit more subtle, and we won't worry about it.

  4. From this postulate we expect a distribution of velocities. (Zumdahl figure 5.20, p 219)

Plot of the Maxwell-Boltzman Distribution of gas particles at different temperatures

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Note that for kinetic energy, KE = 1/2 mV2, so V varies as the square root of the mass (m1/2). Notice also that the energy increases with the square of the velocity. (This is why an accident at 60 mph (88 ft/s) is much worse that one at 30 mph - four times as much energy is involved!)

© R A Paselk

Last modified 27 February 2013