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Kinetic Theory of Matter . Why Johnny can’t sit still (Johnny is a gas particle). Kinetic model of gases . Ideal gas particles are point masses Particles travel in a straight line until they run into something – around 100 -1000 m/s Collisions with walls of container cause pressure

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kinetic theory of matter

Kinetic Theory of Matter

Why Johnny can’t sit still (Johnny is a gas particle)

kinetic model of gases
Kinetic model of gases
  • Ideal gas particles are point masses
  • Particles travel in a straight line until they run into something – around 100 -1000 m/s
    • Collisions with walls of container cause pressure
    • Diffusion – dispersion of a gas by random motion – heavier gases diffuse more slowly
kinetic model of gases1
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
kinetic model of gases2
Kinetic model of gases

Plot of speed vs. # molecules

kinetic model of gases3
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
properties of gases
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)
kinetic model of liquids
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
kinetic model of liquids1
Kinetic model of liquids
  • Particles cannot move in a straight line
  • Particles vibrate along random paths
  • Higher temp means more vibration and faster speed
kinetic model of solids
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)
liquid crystals
Liquid crystals
  • Substances that lose organization in only one dimension as they melt
  • Used in electronic displays because their characteristics change with electric charge
plasmas
Plasmas
  • Most like gases
  • Composed of ions and subatomic particles at high energy – candle flame, fluorescent lights
kinetic energy and temperature
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)
kinetic energy and temperature1
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 = 25 + 273 = 298K (no “º”)

kinetic energy and temperature2
Kinetic energy and temperature
  • Kelvins are directly proportional to kinetic energy
    • Molecules at 400K have twice as much energy as molecules at 200K
  • Degrees Celsius are not directly proportional to kinetic energy
mass and energy
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
mass and energy1
Mass and energy
  • Consider the following gases

He at 300K Rnat 300K

H2 at 100K Br2 at 100K

  • In which gas are the molecules moving the fastest?
  • In which gas are particles moving the slowest?
specific heat capacity
Specific heat capacity
  • Heat it takes to raise the temperature of one gram of stuff 1ºC
  • Unit is J/gºC; symbol is CP
  • Metals have low heat capacity
  • Water has a very high heat capacity (4.184J/gºC, or 1cal/gºC)
specific heat capacity1
Specific heat capacity
  • q = mCPT
  • Find the heat necessary to raise the temperature of a 5g slug of lead from 22-100ºC. CP for lead = 0.13J/gºC
  • H = mCPT = 5(0.13)(100-22) = 50.7J
changing state
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
liquid state to gas state
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
liquid state to gas state1
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 calorie is the heat necessary to raise the temperature of 1g of water 1ºC. 1 cal = 4.184 J
liquid state to gas state2
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)
liquid state to gas state3
Liquid state to gas state
  • Heat = mHv
  • Find the heat necessary to boil 230g water.
  • Heat = 230gx2260J/g

= 519,800 Joules

solid state to liquid state
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 substance freezes – Hf = 334J/g for water
solid state to liquid state1
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
sublimation
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
sublimation1
Sublimation
  • Sublimation involves heat transfer from the surroundings to the substance
  • Opposite process is deposition (heat goes from substance to surroundings)