kinetic molecular models of liquids and solids

These conditions will decrease the both the frequency of molecule-wall collisions and the number of collisions per unit area, the combined effects of which balance the effect of increased collision forces due to the greater kinetic energy at the higher temperature.

This will result in greater average distances traveled by the molecules to reach the container walls, as well as increased wall surface area. If the temperature of a gas is increased, a constant pressure may be maintained only if the volume occupied by the gas increases. If the volume is held constant, the increased speed of the gas molecules results in more frequent and more forceful collisions with the walls of the container, therefore increasing the pressure ( ). If the temperature is increased, the average speed and kinetic energy of the gas molecules increase. Recalling that gas pressure is exerted by rapidly moving gas molecules and depends directly on the number of molecules hitting a unit area of the wall per unit of time, we see that the KMT conceptually explains the behavior of a gas as follows: The Kinetic-Molecular Theory Explains the Behavior of Gases, Part I Then, we will more carefully consider the relationships between molecular masses, speeds, and kinetic energies with temperature, and explain Graham’s law. We will first look at the individual gas laws (Boyle’s, Charles’s, Amontons’s, Avogadro’s, and Dalton’s laws) conceptually to see how the KMT explains them. The various gas laws can be derived from the assumptions of the KMT, which have led chemists to believe that the assumptions of the theory accurately represent the properties of gas molecules. The test of the KMT and its postulates is its ability to explain and describe the behavior of a gas. The average kinetic energy of the gas molecules is proportional to the kelvin temperature of the gas.

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

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

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

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

(Note: The term “molecule” will be used to refer to the individual chemical species that compose the gas, although some gases are composed of atomic species, for example, the noble gases.) This theory is based on the following five postulates described here. The kinetic molecular theory (KMT) is a simple microscopic model that effectively explains the gas laws described in previous modules of this chapter. Although the gas laws describe relationships that have been verified by many experiments, they do not tell us why gases follow these relationships. The mathematical forms of these laws closely describe the macroscopic behavior of most gases at pressures less than about 1 or 2 atm. The gas laws that we have seen to this point, as well as the ideal gas equation, are empirical, that is, they have been derived from experimental observations.

Use this theory’s postulates to explain the gas laws.

State the postulates of the kinetic-molecular theory.

Kinetic molecular models of liquids and solids