FridayFebruary 25, 2011

(The Nature of Gases)

The Kinetic-Molecular

Theory of Gases can be used to

explain the properties of

gases in terms of:

Bell RingerFriday, 2-25-11

the energy of the gas

particles,and the forces

that act between the gas particles.

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Be sure to have all of your work turned in or

remediated by this afternoon!

Six-Week’s Assignment List Date Issued Date Due

WS: Chemical Reactions and EquationsPart 1 1/19 1/26

WS: Word Equations and Formula Equations 1/20 1/27

Quiz: Word Equations and Formula Equations 1/21 1/21

WS: Chemical Reactions and EquationsPart 2 1/24 1/28

WS: Chemical Reactions and EquationsPart 3 1/25 1/31

Lab: Types of Reactions 1/28 1/31

WS: Chemical Reactions and EquationsPart 4 1/27 2/2

Test 6 2/10 2/10

WS: Moles and Molar Mass 2/11 2/18

WS - Practice with Mole–Mass-Numbers of Atoms Conversions 2/14 2/21

WS – Stoichiometry: Mole-Mole Conversions 2/15 2/22

Test 7 2/22 2/22

The Kinetic-Molecular Theory of Gases

The Nature of GasesThe 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 gas is 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.

The Nature of GasesExpansion

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.

The Nature of GasesFluidity

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.

The Nature of GasesLow Density

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.

The Nature of GasesCompressibility

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.

The Nature of GasesDiffusion 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.

The Nature of GasesDiffusion 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.

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The Kinetic Molecular Theory and Nature of Gases