topic: kinetic-molecular theory (kmt) do now: packet page __ relationship between temp and average...
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TOPIC: Kinetic-Molecular TOPIC: Kinetic-Molecular Theory (KMT)Theory (KMT)
Do Now: packet page __Do Now: packet page __
Relationship between Temp Relationship between Temp and Average Kinetic Energyand Average Kinetic Energy
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) as it pertains to (KMT) as it pertains to
ideal gasesideal gasesThere are 4 assumptions to the KMT
Real vs. ideal gasReal vs. ideal gas
• Ideal gasIdeal gas obeys assumptions of KMT obeys assumptions of KMT all the time all the time • ItIt’’s s a modela model
• It It doesndoesn’’t existt exist
• Real gasesReal gases follow KMT most of time, follow KMT most of time, but but notnot at at high pressure & low high pressure & low temperaturetemperature• KMT breaks down when molecules are KMT breaks down when molecules are
close togetherclose together
1) Gases consist of spherical 1) Gases consist of spherical molecules moving in constant, molecules moving in constant, random, straight-line motionrandom, straight-line motion
Random, straight-line?Random, straight-line?
- move in straight- move in straight
lines until hit lines until hit
something, then can something, then can
bounce bounce
off at any angleoff at any angle
2) Gas particles undergo 2) Gas particles undergo ““elasticelastic”” collisions with each other and collisions with each other and with walls of containerwith walls of container
““ElasticElastic”” means total KE is means total KE is conservedconserved
• KE does KE does notnot get converted to heat get converted to heat or sound or any other kind of or sound or any other kind of energyenergy
• KE KE cancan be transferred between be transferred between particlesparticles
3) Gas molecules separated by such 3) Gas molecules separated by such great distances that the volume of great distances that the volume of molecule is negligible (not molecule is negligible (not significant)significant)
• Ideal gasses are considered not to have Ideal gasses are considered not to have volume, but they still have a mass, so volume, but they still have a mass, so scientists call this a point massscientists call this a point mass
4)4) Gas molecules do not attract or Gas molecules do not attract or repel each otherrepel each other
4)4) Real gases do interact with one Real gases do interact with one another…that’s why water vapor another…that’s why water vapor condenses…condenses… Intermolecular
forces
Ideal vs RealIdeal vs Real
• IdealIdeal• Particles Particles
themselves themselves take up no take up no spacespace
• Particles have Particles have no no intermolecular intermolecular forcesforces
• Real ( at Real ( at high high pressure & low pressure & low temperature)temperature)• Particles take up Particles take up
space (they have space (they have volume)volume)
• All gas particles All gas particles are subject to are subject to intermolecular intermolecular interactions interactions
Example: N2(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
• http://ed.ted.com/lessons/describing-the-invisible-properties-of-gas-brian-bennett
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