Chapter 9. Section 5 - Kinetic Molecular Theory

Elastic Collision

A collision between molecules that does not involve a loss of energy.

Kinetic Molecular Theory (KMT)

A simple microscopic model that effectively explains many gas laws.

Avogadro's Law

At constant pressure and temperature, the frequency and force of molecule-wall collisions are constant. Increasing the number of gaseous molecules will require a proportional increase in the container volume to yield a decrease in the number of collisions per unit area to compensate for the increased frequency of collision.

Dalton's Law

Because of the large distances between them, the molecules of one gas in a mixture bombard the container walls with the same frequency whether other gases are present or not, and the total pressure of a gas mixture equals the sum of the (partial) pressures of the individual gases.

KMT - Postulate 4.

Gas molecules exert no attractive forces on each other or the container walls; therefore, their collisions are elastic (do not involve a loss of energy).

KMT - Postulate 1.

Gases are composed of molecules that are in continuous motion, traveling in straight lines and changing direction only when they collide with other molecules or with the walls of a container.

Boyle's Law

If the gas volume is decreased, the container well area decreases and the molecule-wall collision frequency increases, both of which increase the pressure exerted by the gas.

Amonton's Law

If the temperature is increased, the average speed and kinetic energy of the gas molecules increase. If the volume is held constant, the pressure increases with increased temperature.

Charles's Law

If the temperature of a gas is increased, a constant pressure may be maintained only if the volume occupied by the gas increases. However, the increased volume causes surface area to increase, and molecule collisions per unit area decreases. This results in a net decrease in gas pressure.

KMT - Postulate 5.

The average kinetic energy of the gas molecules is proportional to the kelvin temperature of the gas.

KMT - Postulate 2.

The molecules composing the gas are negligibly small compared to the distances between them.

KMT - Postulate 3.

The pressure exerted by a gas in a container results from collisions between the gas molecules and the container walls.