Kinetic Molecular Theory (KMT)1. Gases consist of large numbers of molecules that are in

continuous, random motion. 2. The volume of all of the gas molecules is negligible

compared to the total volume that the gas occupies.3. Attractive and repulsive forces between gas molecules

are negligible.4. Collisions between gas molecules are perfectly elastic

(energy is not lost from collisions).5. The average kinetic energy of the molecules is directly

proportional to the absolute temperature. At any given temperature, the molecules of all gases have the same kinetic energy.

• All real gases will show some deviations from ideal behavior.

• The greatest deviations will occur when: –Gases are under very high pressure.

–Gases are at a very low temperature.

• Remember that because K.E. = ½ mv2, heavier gas particles will move at slower speeds than lighter ones.

– K.E. = ½ mv2

– Because all gases have the same kinetic energy, for one mole: – ½ (MMA)vA

2 = ½ (MMB)vB2

– This equation can be used to determine an unknown speed for a gas.

• Effusion = escape of gas molecules through a hole.

• Diffusion = the spread of one substance throughout a space or throughout a second substance.

• Graham’s Law of Effusion – relates the rates of effusion of two different gases (r1 and r2) to their molar masses.