Friday February 25 , 2011

1. FridayFebruary 25, 2011 (The Nature of Gases)

2. Bell RingerFriday, 2-25-11 The Kinetic-Molecular Theory of Gases can be used to explain the properties of gases in terms of: the energy of the gas particles, and the forces that act between the gas particles.

3. Announcements Be sure to have all of your work turned in or remediated by this afternoon!

5. The Kinetic-Molecular Theory of Gases

6. The Nature of Gases The kinetic-molecular theory applies only to ideal gases. Although ideal gases do not actually exist, many gases behave nearly ideally if pressure is not very high or temperature is not very low. When their particles are far enough apart and have enough kinetic energy, most gases behave ideally. However, all real gases deviate to some degree from ideal-gas behavior. A real gasis a gas that does not behave completely according to the assumptions of the kinetic-molecular theory. Let’s look at how the kinetic-molecular theory accounts for the physical properties of gases.

7. The Nature of Gases Expansion Gases do not have a definite shape or a definite volume - they completely fill any container in which they are enclosed, and they take its shape. A gas transferred from a one-liter vessel to a two-liter vessel will quickly expand to fill the entire two-liter volume. According to the kinetic-molecular theory, gas particles move rapidly in all directions without significant attraction or repulsion between them.

8. The Nature of Gases Fluidity Because the attractive forces between gas particles are insignificant, gas particles glide easily past one another - this ability to flow causes gases to behave similarly to liquids. Because liquids and gases flow, they are both referred to as fluids.

9. The Nature of Gases LowDensity The density of a substance in the gaseous state is about 1/1000 the density of the same substance in the liquid or solid state. That is because the particles are so much farther apart in the gaseous state.

10. The Nature of Gases Compressibility During compression, the gas particles, which are initially very far apart, are crowded closer together; therefore, the volume of a given sample of a gas can be greatly decreased. Steel cylinders containing gases under pressure are widely used in industry - when they are full, such cylinders may contain 100 times as many particles of gas as would be contained in non-pressurized containers of the same size.

11. The Nature of Gases Diffusion and Effusion Gases spread out and mix with one another, even without being stirred. If the stopper is removed from a container of ammonia in a room, ammonia gas will mix uniformly with the air and spread throughout the room. The random and continuous motion of the ammonia molecules carries them throughout the available space. Such spontaneous mixing of the particles of two substances caused by their random motion is called diffusion.

12. The Nature of Gases Diffusion and Effusion Diffusion is a process by which particles of a gas spread out spontaneously and mix with other gases. In contrast, effusion is a process by which gas particles pass through a tiny opening. The rates of effusion of different gases are directly proportional to the velocities of their particles. Because of this proportionality, molecules of low mass effuse faster than molecules of high mass.

13. Continue Worksheet The Kinetic Molecular Theory and Nature of Gases