Unit 7-Behavior of Gas Unit 7-Behavior of Gas MoleculesMoleculesKinetic Molecular Theory

Collision Theory of Gas Molecules

The behavior of gas molecules is understood by:

◦Applying the Kinetic Molecular Theory(Considering the motion and arrangement of molecules)

◦Applying Collision Theory of Gas Molecules

Kinetic Molecular TheoryKinetic Molecular TheoryKinetic Molecular Theory is based on the

idea that particles of matter are always in motion. This applies to matter of all states including gas.

Temperature measures the average kinetic energy of the particles in a sample of matter (Kinetic Energy = ½ mv2).

SolidsSolids Particles are held in a relative fixed

position to each other. They do vibrate in place. Therefore solids have definitive shape.

Particles are very tightly packed and have extremely low kinetic energy.

Attractive forces between particles are much more effective, compared to other states, due the reduced distance between them.

Very organized

Highest density

Incompressible

LiquidsLiquids Particles are in constant motion, not bound to a fixed

position, and flow freely (fluid), hence, they have no shape.

Particles are closer together with lower kinetic energy.

Attractive forces between particles are more effective than in gases as a result of the reduced distance between them, causing liquids to have a fixed volume.

More ordered than gases

More dense than gases and less dense than solids

Much less compressible than gases because liquid particles are already much closer together.

GasesGases Particles are in constant and random

motion, not bound to a fixed position and flow freely (fluid), hence, gases have no shape.

Particles are far apart and have high kinetic energy.

Attractive forces between particles are far less effective due to the distance between the particles. As a result gases have no fixed volume.

Disordered

Low density

Very compressible: lots of empty space.

Collision Theory of Gas MoleculesCollision Theory of Gas Molecules Gas particles are in motion that is called

Brownian motion – the best way to understand this motion is by calling it “random”.

Collisions occur both with the boundary of the container and each other. The types of collisions are not perfectly elastic, but they are very close to elastic.

Gas molecules will be attracted by both electrostatic and gravitational forces. The effects of this force is miniscule and is ignored.

Gas molecules clearly have both mass and volume. The volume is so small, however, that each gas molecule is said to be a point without volume.

Brownian Motion

Elastic Collision

Intermolecular Forces

Ideal vs. Real GasIdeal vs. Real Gas

Ideal Gas◦ Motion is totally random

◦ All collisions are elastic

◦ Gas molecules do not have any intermolecular attraction

◦ Gas molecules have no volume

Real Gas◦ Motion is Brownian (almost

but not quite random)

◦ Collisions are not perfectly elastic

◦ Gas molecules experience intermolecular attraction

◦ Gas molecules have volume

Application to Gas LawsApplication to Gas LawsFor all of the Gas Laws, the gases

involved are assumed to be Ideal Gases.

The difference between the behavior of Real and Ideal Gases is so small that except in very sensitive laboratory environments the difference can be ignored.