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Kinetic-Molecular Theory

Kinetic-Molecular Theory. Mr. Lambert. The Kinetic Molecular Theory. Gases consist of a large number of molecules that are in continuous, random movement. The volume of the molecules of the gas is negligible(meaning of no value) compared to the total volume in which the gas is contained.

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Kinetic-Molecular Theory

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  1. Kinetic-Molecular Theory Mr. Lambert

  2. The Kinetic Molecular Theory Gases consist of a large number of molecules that are in continuous, random movement. The volume of the molecules of the gas is negligible(meaning of no value) compared to the total volume in which the gas is contained. Attractive forces between gas molecules are assumed to be zero.

  3. KMT #1 • Gases consist of a large number of molecules that are in continuous, random movement. • There is a great distance between gas molecules, so the molecules travel in straight lines between collisions at the walls and each other. • These collisions randomize the motion of the molecules. • Most of the collisions between molecules are binary, in that only two molecules are involved.

  4. KMT #2 • The volume of the molecules of the gas is negligible compared to the total volume in which the gas is contained • Small molecules are therefore on the order of 10 angstroms in diameter, or less than 10-24- L in Molecular Volume. • Molecular volumes and container volumes are incomparable to one another when Molecular volumes exceed 1mol/L. • The more mols of gas you have, the more space you take up.

  5. KMT #3 • Attractive forces between gases are assumed to be zero. • We know that if these forces were significant, the molecules would stick together. • The attractive forces DO make gases stick together, sometimes, only at certain temperatures. Think about rain. • For an ideal gas, we can assume that those attractive forces are not just small, but identically zero.

  6. Consequences of KMT • The average kinetic energy of the molecules does not change with time. • The molecules bounce and bounce but, on average, do not slow down as long as temperature of the gases remain constant. Why? • Energy can be transferred between molecules during collisions but not lost because the collisions are perfectly elastic. Think rubber bands. • The average kinetic energy of the molecules is proportional to absolute temperature (a result of thermodynamics). • At a given temperature the molecules of all species of gas, no matter what shape or weight, have the same average kinetic energy.

  7. The Molecular Picture of Pressure • The pressure of a gas is manifested: • at the boundary of the vessel it is confined in, and is caused by collisions of the molecules of the gas with the walls of the container. • The magnitude of the pressure is related to how hard and how often the molecules strike the wall.

  8. Absolute Temperature • The absolute temperature of a gas is a measure of the average kinetic energy of its’ molecules. • If two different gases are at the same temperature, their molecules have the same average kinetic energy. • If the absolute temperature of a gas is doubled, the average kinetic energy of its molecules if doubled. • If the temperature approaches absolute zero, the kinetic energy of the molecules approach zero and they stop. • Absolute zero = 0 K or -273 degrees C

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