chapter 13 states of matter. kinetic energy = energy of motion kinetic theory = all matter consists...
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• Kinetic Energy = Energy of motion
• Kinetic Theory = all matter consists of particles in constant motion
Average Kinetic Energy• at any given temperature the particles of all
substances have the same average kinetic energy
• No kinetic energy = no movement = absolute zero
• Absolute zero = -273.15oC or 0 K (Kelvin)
Let’s Learn:
How heat spreads from one region to another.
Examples:
How the whole copper rod get hot when we heat one end
How does the heat spread throughout the whole pot of water when we are only heating the bottomHow does the heat from the Sun reaches us
What Happens???• All things are made up of particles• When things get heated, they absorb heat
energy.• This means that the particles are absorbing the
heat energy With more energy, the particles are able to move faster
• When the particles move faster, the temperature of the object increases.
• Temperature increase means the object gets hotter.
CONDUCTION• Occurs mainly in solids• Two types of conduction
Molecular vibrationFree electron diffusion
Note: Conduction is not the main form of heat transfer in liquids and gases because their molecules are spaced further apart.
Molecular Vibration
•When heat is supplied to one end, the molecules at the hot end start to vibrate more vigorously.
•In the process, they ‘bump’ into their neighboring molecules. In doing so, some energy is transferred to the neighbor.
•The neighbor molecule gains energy and starts to vibrate more vigorously. The cycle continues.
Conduction Animation
http://www.scienceonline.co.uk/flash/solid.html
http://www.bbc.co.uk/schools/gcsebitesize/physics/energy/energytransferrev6.shtml
Free Electron Diffusion
•This form of conduction takes place only in metals. As only metals have free electrons.
•The electrons are freed from the molecule when heated and they travel towards the cold end.
•At the cold end they collide into a molecule therefore passing all their energy to the molecule.
Comparing the 2 Mechanisms
Molecular vibration Free electron diffusion
Occurs in all solids
Slow process
Occurs in metals only
Fast process
This explains why metals heat up faster:
1. Metals have 2 mechanisms of conduction occuring at the same time.
2. In metals, free electron diffusion is the main mechanism, which is faster.
Conductors and Insulators
• Materials that can conduct heat easily and readily (eg. Metals) are known as conductors.
• Materials that do not conduct heat easily (eg. Water, air, plastic) are known as insulators.
Convection• Occurs in liquids and gases• Does not occur in solids because the molecules
are not free to move around
What happens during convection?Taking the example of heating water• Water at the bottom is heated first• Heated water expands• When water expands density decreases• Heated water of lower density starts to rise• Cooler water of higher density rushes in from sides
to take its place• The cooler water gets heated and the cycle repeats.• Convection currents are set up.• http://www.bbc.co.uk/schools/gcsebitesize/physics/energy/
energytransferrev6.shtml
Radiation• Radiation does not require a medium to
transfer heat. (can occur in a vacuum)• Sun releases electromagnetic waves
(heat is contained in the waves as infra-red)
• Hotter objects radiates more heat.
LIQUID!liquid
assumes the shape of the part of the container retains its volume
not easily compressed
flows easily
Characteristics of Solids, Liquids and Gases
gas liquid solid
takes the shape and volume of its
container
Volume remains the same, takes shape of
container
Keeps its shape and volume
easily compressed not easily compressed not easily compressed
flows easily flows easily does not flow easily
Cool Cool
SOLID!solid
Ordered arrangement
rigid - particles locked into place/fixed
little free space between particles
LIQUID!liquid
disorder
particles can move/slide past one another
little free space between particles
GAS!gas
total disorder motion: constant, rapid, random
lots of free space between particles
Collisions are elastic – total kinetic energy remains constant
Molecular Level Comparison of Solids, Liquids and Gases
solid liquid gas
Ordered arrangementdisorder
total disorder motion: constant,
rapid, random
rigid - particles locked into place/fixed
particles can move/slide past one another
lots of free space between particles
little free space between particles
little free space between particles
Collisions are elastic – total kinetic energy
remains constant
Cool Cool
Evaporation• Vaporization = the conversion of a liquid to a gas
or vapor
• Evaporation = vaporization that occurs on the surface of a liquid that is not boiling
• Only those molecules with certain minimum kinetic energy can escape from the surface of a liquid
• Evaporation rate increases when a liquid is heated…heat increases the average kinetic energy which allows particles to overcome the attractive forces that keep them in the liquid state
Vapor Pressure• Vapor pressure = measure of the force
exerted by the gas above a liquid
• Constant vapor pressure = a dynamic equilibrium exists between the vapor and the liquid. The rate of evaporation = rate of condensation.
Animation of Dynamic Equilibriumhttp://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/vaporv3.swf
Boiling• Liquid in an open container
is heated• Temperature increases• Particles throughout the liquid
have enough kinetic energy to vaporize• The liquid begins to boil• Bubbles of vapor form in the liquid, rise to the
surface, and escape into the air• Boiling point = temperature at which the vapor
pressure of the liquid = external pressure on the liquid
Effect of Pressure On Boiling Point• Lower pressure would lower the boiling point of water.• Water will boil very quickly on the mountain top but the
temperature reached is lower than 100oC.• Increasing pressure would raise the boiling point of water.• Water will boil at a higher temperature above 100oC.
Melting• Heat is applied• Particles vibrate as kinetic energy increases• Organization of the solid breaks down• The attractions that hold the particles in fixed
positions are overcome• Solid melts• Melting Point = temperature at which a solid melts
into a liquid• Freezing Point = Melting Point – they are the
same temperature and liquid and solid are in equilibrium
Sublimation• Occurs in solids with vapor pressures that
exceed atmospheric pressure at or near room temperature.
• A direct change from solid to vapor
Video of Iodine Sublimationhttp://www.youtube.com/watch?v=E-fs9OwE9Y0
Phase Diagram• A graph showing the relationships between
solid, liquid, vapor states (or phases) of a substance in a sealed container.
• Lines on the graph = conditions of pressure and temperature at which two phases exist in equilibrium
• Triple point = represents the only set of conditions in which all three phases are present in equilibrium