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 Diffusion – dispersion of a gas by random motion – heavier gases diffuse more slowly
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
Plot of speed vs. # molecules Kinetic model of gases Plot of speed vs. # molecules
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 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 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 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 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 Substances that lose organization in only one dimension as they melt Used in electronic displays because their characteristics change with electric charge
Plasmas Most like gases Composed of ions and subatomic particles at high energy – candle flame, fluorescent lights
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 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 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
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 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?
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 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 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
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 state Heat = mHv Find the heat necessary to boil 230g water. Heat = 230gx2260J/g = 519,800 Joules
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
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
Heating curves
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
Sublimation Sublimation involves heat transfer from the surroundings to the substance Opposite process is deposition (heat goes from substance to surroundings)