Some Particular Properties of Gases
As the temperature of a gas is increased, its kinetic energy is increased, thereby
increasing the random motion. At a particular temperature not all the particles
have the same kinetic energy, but the temperature is a measure of the average
kinetic energy of the particles. A graph of the various kinetic energies resembles a
normal bell-shaped curve with the average found at the peak of the curve (see
Figure 20).
TIP
When you read the temperature of a substance, you are measuring its average kinetic
energy.Figure 20. Molecular Speed Distribution in a Gas at Different TemperaturesTIP
Diffusion means spreading out.When the temperature is lowered, the gas reaches a point at which the kinetic
energy can no longer overcome the attractive forces between the particles (or
molecules) and the gas condenses to a liquid. The temperature at which this
condensation occurs is related to the type of substance the gas is composed of and
the type of bonding in the molecules themselves. This relationship of bond type to
condensation point (or boiling point) is pointed out in Chapter 3, “Bonding.”
The random motion of gases in moving from one position to another is
referred to as diffusion. You know that, if a bottle of perfume is opened in one
corner of a room, the perfume, that is, its molecules, will move or diffuse to all
parts of the room in time. The rate of diffusion is the rate of the mixing of gases.