The Kinetic-Molecular Theory of Matter with

Gases

Section 10.1

Behavior of Particles

• Kinetic-molecular theory: a theory that explains the behavior of systems based on the idea that particles of matter are always in motion

• Explains properties of matter in terms of the energy of the particles and the forces that act between them

Kinetic-Molecular Theory of Gases

• The theory provides a model for an ideal gas

• Ideal gas: a hypothetical gas that perfectly fits all the assumptions of the kinetic-molecular theory

• Real gas: a gas that does not behave completely according to the assumptions of the kinetic-molecular theory

5 Assumptions 1. Gases consist of large numbers of tiny

particles that are far apart relative to their size

2. Collisions between gas particles and between particles and container walls are elastic collisions

• Elastic collision: one in which there is no net loss of total kinetic energy (energy is transferred between the particles)

Elastic Collision

Assumptions3. Gas particles are in continuous, rapid,

random motion. They therefore possess kinetic energy

4. There are no forces of attraction between gas particles

5. The temperature of a gas depends on the average kinetic energy of the particles of the gas

Random Motion of Gases

Physical Properties

• Expansion• Gas particles move rapidly in all

directions with no attraction• This explains why gases do not have a

definite shape or volume• They completely fill the container and

take its shape

Fluidity

• Gas particles slip and slide past each other easily

• They flow like liquids• Both liquids and gases are referred to as

fluids

Low Density and High Compressibility

• The particles are very far apart from each other

• Very low density because of D = m/V• The gas particles can be crowded closer

together• The volume can be greatly decreased by

compressing the gas

Diffusion

• Diffusion: spontaneous mixing of the particles of two substances caused by their random motion

• Gases spread out without being stirred• The gas particles will move throughout

the available volume

Effusion

• Effusion: a process by which gas particles pass through a tiny opening

• An example of this would be the air coming out of a polymer balloon

• Molecules of low mass effuse faster than molecules of high mass (the low mass molecules move faster)

Deviations of Real Gases from Ideal Behavior

• All real gases deviate from ideal behavior to some extent

• At very high pressure and low temperatures, real gases are least likely to behave ideally

• At low pressure and high temperature, real gases are most likely to behave ideally

• Gases whose particles have low attraction for each other, like the noble gases, behave close to ideally

• The more polar the molecule of gas, the least likely it is to behave ideally