TOPIC: Kinetic-Molecular Theory (KMT) Do Now: packet page __ Relationship between Temp and Average Kinetic Energy

Models Scientists use models because simpler than real lifeScientists use models because simpler than real life Kinetic-molecular theory can be extended to all phases of matterKinetic-molecular theory can be extended to all phases of matter

Kinetic-Molecular Theory (KMT) as it pertains to ideal gases There are 4 assumptions to the KMT

Real vs. ideal gas Ideal gas obeys assumptions of KMT all the timeIdeal gas obeys assumptions of KMT all the time It’s a modelIt’s a model It doesn’t existIt doesn’t exist Real gases follow KMT most of time, but not at high pressure & low temperatureReal gases follow KMT most of time, but not at high pressure & low temperature KMT breaks down when molecules are close togetherKMT breaks down when molecules are close together

1) Gases consist of spherical molecules moving in constant, random, straight-line motion Random, straight-line? - move in straight - move in straight lines until hit lines until hit something, then can bounce off at any angle

2) Gas particles undergo “elastic” collisions with each other and with walls of container “Elastic” means total KE is conserved “Elastic” means total KE is conserved KE does not get converted to heat or sound or any other kind of energyKE does not get converted to heat or sound or any other kind of energy KE can be transferred between particlesKE can be transferred between particles

3) Gas molecules separated by such great distances that the volume of molecule is negligible (not significant) Ideal gasses are considered not to have volume, but they still have a mass, so scientists call this a point massIdeal gasses are considered not to have volume, but they still have a mass, so scientists call this a point mass

4)Gas molecules do not attract or repel each other

4)Real gases do interact with one another…that’s why water vapor condenses… Intermolecular forces

Ideal vs Real IdealIdeal Particles themselves take up no spaceParticles themselves take up no space Particles have no intermolecular forcesParticles have no intermolecular forces Real ( at high pressure & low temperature)Real ( at high pressure & low temperature) Particles take up space (they have volume)Particles take up space (they have volume) All gas particles are subject to intermolecular interactionsAll gas particles are subject to intermolecular interactions

Example: N 2 (g) At a low temperature, the kinetic energy is… low, which means their intermolecular forces are strong enough to hold them together Nitrogen gas become liquid Nitrogen

Propane If you increase the pressure, the volume… decreases, which forces particles closer together. They will become a liquid

VIDEO LINK invisible-properties-of-gas-brian-bennetthttp://ed.ted.com/lessons/describing-the- invisible-properties-of-gas-brian-bennett