1. Kinetic Theory of Matter
Why Johnny can’t sit still (Johnny is a gas particle)

2. Kinetic model of gases Ideal gas particles are point masses
Particles travel in a straight line until they run into something – around m/s
Collisions with walls of container cause pressure
Diffusion – dispersion of a gas by random motion – heavier gases diffuse more slowly

3. Kinetic model of gases
Collisions are perfectly elastic – no other interactions between gas particles – like air hockey pucks
Temperature is related to the average kinetic energy of the gas molecules – higher temp = faster speed

4. Plot of speed vs. # molecules
Kinetic model of gases
Plot of speed vs. # molecules

5. Kinetic model of gases
Brownian motion – Random motion of suspended particles in liquid or gas
Due to collisions between particles and atoms of gas or liquid
Used by Einstein to prove atomic theory of matter

6. Properties of gases Gases can flow
Gases take the shape of the container
Gases have no definite volume
Gases and liquids are fluids (anything that can flow)

7. Kinetic model of liquids
Particles are much closer together than gases
Interparticle interactions are significant
Particles slide past each other like magnetized marbles
Flow
Take shape of container
Have a definite volume

8. Kinetic model of liquids
Particles cannot move in a straight line
Particles vibrate along random paths
Higher temp means more vibration and faster speed

9. Kinetic model of solids
Particles vibrate in place
Higher temp means faster/wider vibrations
Crystalline solids – regular arrangement of particles (salt, diamond)
Amorphous solid – random arrangement (wax, rubber, glass)

10. Liquid crystals
Substances that lose organization in only one dimension as they melt
Used in electronic displays because their characteristics change with electric charge

11. Plasmas Most like gases
Composed of ions and subatomic particles at high energy – candle flame, fluorescent lights

12. Kinetic energy and temperature
Temperature scales
Celsius – based on melting point (0ºC) and boiling point (100ºC) of water
Kelvin – based on absolute zero (temperature at which all atomic movement ceases)

13. Kinetic energy and temperature
Kelvins are the same size as ºC
Absolute zero is the same as –273ºC
K=C+273
Find the Kelvin equivalent of room temperature (25ºC)
K = = 298K (no “º”)

14. Kinetic energy and temperature
Kelvins are directly proportional to kinetic energy
Molecules at 400K move twice as fast as molecules at 200K
Degrees Celsius are not directly proportional to kinetic energy

15. Mass and energy Kinetic energy depends on mass and speed
At the same temperature, heavier molecules move more slowly
Heavier molecules diffuse more slowly than light ones

16. Mass and energy Consider the following gases He at 300K Ra at 300K
H2 at 100K Br2 at 100K
In which gas are the molecules moving the fastest?
In which gas are particles moving the slowest?

17. Changing state Gas – liquid
Evaporation – some molecules of a liquid have enough energy to escape – happens at RT
Boiling point – temperature at which the vapor pressure of a liquid equals the atmospheric pressure

18. Liquid state to gas state
Vapor pressure – pressure exerted by molecules trying to leave the surface of a liquid – increases with increasing temperature
Boiling point depends on:
Molar mass - higher MM, higher BP
Polarity – high polarity, high BP
Atmospheric pressure – high AP, high BP

19. Liquid state to gas state
Heat of vaporization – heat necessary to vaporize one gram of a liquid at its boiling point
Hv = 2260 J/g for water
J = Joule
1 Joule is the heat necessary to raise the temperature of 1g of water 1ºC

20. Liquid state to gas state
Heat transfer – when a liquid boils or evaporates, heat goes from surroundings to the liquid (sweating)
When a gas condenses, heat is transferred from the gas to the surroundings (steam burns)

21. Liquid state to gas state
Heat = mHv
Find the heat necessary to boil 230g water.
Heat = 230gx2260J/g
= 519,800 Joules

22. Solid state to liquid state
Melting – molecules get enough energy to acquire linear motion
Freezing – molecules slow down enough so they get trapped in place
Heat of fusion – heat released when one gram of a substances freezes – Hf = 334J/g for water

23. Solid state to liquid state
Math is the same as for boiling
Find the heat released when 10.0g water freezes to form ice.
q = Hfxm = 10.0gx334J/g = 3340J
Heat transfer happens without temperature changes during phase change

24. Heating curves

25. Sublimation Solid – gas – sublimation – happens when pressure is low
Dry ice and iodine sublime readily at standard atmospheric pressure
Below freezing, ice will sublime slowly
Many substances can be made to sublime under a vacuum

26. Sublimation
Sublimation involves heat transfer from the surroundings to the substance
Opposite process is deposition (heat goes from substance to surroundings)