Properties of Gases

1. Properties of Gases Kinetic Molecular Theory

2. Kinetic-Molecular Theory • Based on idea that particles of matter are always in motion. • Provides reasoning for the behavior of gases and their physical properties.

3. Assumptions of the Kinetic-Molecular Theory • 1. Gases consist of a large number of tiny particles that are far apart relative to their size. • Most of the volume of a gas is empty space. • Accounts for lower density of gases in comparison to solids and liquids. • Explains fact that gases are easily compressed.

4. Assumptions of the Kinetic-Molecular Theory • 2. Gas particles are in continuous rapid, random motion • Kinetic energy is the energy of motion. • 3. There are no forces of attraction or repulsion between gas particles. • Kinetic energy of the gas particles overcomes the attractive forces between the individual particles.

5. Assumptions of the Kinetic-Molecular Theory • 4. The average kinetic energy (KE) of gas particles depends on the temperature of the gas. • As temperature increases, KE increases. • KE = ½mv2 (m = mass, v = velocity). • At the same temperature: • Lighter gases have higher average speeds. • Heavier gases have lower average speeds.

6. Assumptions of the Kinetic-Molecular Theory • 5. Collisions between gas particles and between particles and container walls are elastic collisions. • In elastic collisions, there is no loss of kinetic energy. • Kinetic energy is transferred between two gas particles during collisions. http://my.hrw.com/sh/hc6_003036809x/student/ch10/sec01/vc00/hc610_01_v00fs.htm

7. Ideal versus Real Gases • Ideal gases conform to all of the assumptions of the kinetic-molecular theory of gases. • Gases that behave ideally have the following properties: • Low mass. • Low polarity. • Gases behave most ideally under the following conditions: • High temperature. • Low pressure.

8. Ideal versus Real Gases • Real gases do not obey all of the assumptions of the kinetic-molecular theory. • Gases that behave like real gases have the following properties: • High mass. • High polarity. • Gases behave like real gases under the following conditions: • Low temperature. • High pressure.

9. Properties of Gases • Expansion and compression: • Gases can expand or compress to fit any size container. • Gases have no definite shape or volume. • Fluidity: • Gas particles easily flow past one another. • Low density: • The gaseous state of a substance is 1/1000th the density of the same substance as a solid or liquid.

10. Properties of Gases • Diffusion and effusion: • Diffusion is the mixing of the particles of two gaseous substances caused by their random motion. • Effusion is the process by which gas particles pass through a tiny opening. • Both occur spontaneously. http://my.hrw.com/sh/hc6_003036809x/student/ch10/sec01/vc05/hc610_01_v05fs.htm