Kinetic-Molecular TheoryKinetic-Molecular Theory(KMT)(KMT)

ModelsModels

•scientists use models scientists use models because simpler than real lifebecause simpler than real life

•Kinetic-Molecular Theory can Kinetic-Molecular Theory can be extended to all phases of be extended to all phases of mattermatter

Kinetic-Molecular Theory Kinetic-Molecular Theory (KMT)(KMT)

lets discuss how pertains to gases:

there are 4 assumptions to the KMT

1) gas1) gaseses consist of spherical consist of spherical moleculesmolecules moving in constant, moving in constant, random, straight-line motionrandom, straight-line motion

random, straight-line?random, straight-line?

- move in straight lines until hit - move in straight lines until hit something, then can bounce off at something, then can bounce off at any angleany angle

Kinetic-Molecular TheoryKinetic-Molecular Theory

2) gas particles undergo “elastic” 2) gas particles undergo “elastic” collisions collisions with each other and with with each other and with walls of containerwalls of container

“ “elastic” means elastic” means total KE is conservedtotal KE is conserved• KE does KE does notnot get converted to heat or get converted to heat or

sound or any other kind of energysound or any other kind of energy• KE KE cancan be transferred between particles be transferred between particles

Kinetic-Molecular TheoryKinetic-Molecular Theory

3) gas molecules 3) gas molecules separated by great separated by great distances thatdistances that volume volume of molecule of molecule is is negligiblenegligible

• distance between molecules is more distance between molecules is more important than actual size of moleculeimportant than actual size of molecule

Kinetic-Molecular TheoryKinetic-Molecular Theory

4) gas molecules do not attract or 4) gas molecules do not attract or repel each otherrepel each other

• assume there are no interactions assume there are no interactions between gas moleculesbetween gas molecules

real vs. ideal gasreal vs. ideal gas

• ideal gasideal gas obeys assumptions of KMT obeys assumptions of KMT all the time all the time • this is this is a model; doesn’t exista model; doesn’t exist

• real gasesreal gases follow KMT most of time follow KMT most of time• NOTNOT at at high pressure & low temperaturehigh pressure & low temperature

KMT breaks down when molecules are close KMT breaks down when molecules are close togethertogether

Review of KMTReview of KMT• What features of the Kinetic-What features of the Kinetic-

Molecular model show real gases Molecular model show real gases behaving like ideal gases?behaving like ideal gases?

• What features of the Kinetic-What features of the Kinetic-Molecular model break down?Molecular model break down?

______ pressure & ______ temperature______ pressure & ______ temperature

______ pressure & ______ temperature______ pressure & ______ temperatureLOWLOW HIGHHIGH

HIGHHIGH LOWLOW