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The OTHER TWO states of matter
LIQUIDS A decrease in the average kinetic energy of gas particles causes the temperature to decrease. As it cools, the particles tend to move more slowly if they slow down enough, attractive forces called van der Waal s forces pull them very close together so they can only slip & slide past each other. It is now in liquid form Condensation Change of a gas to a liquid
The Nature of Liquids The conversion of a liquid to a gas (or vapor) at the surface of a liquid is called vaporization In an open container the process is called evaporation Particles near the surface with enough kinetic energy that happen to bounce in the right direction escape!
The Nature of Liquids Eventually the particles will lose energy and return to the liquid state, or condense. What are the odds that they will return to the original liquid? What if we cover the container? So, the particles begin to evaporate, then some begin to condense. Eventually, the number of particles evaporating will equal the number condensing & the space above the liquid will be saturated with vapor A dynamic equilibrium now exists: the Rate of evaporation = rate of condensation
The Nature of Liquids Note that there will still be particles that evaporate and condense But, there will be no NET change It will LOOK like there s NOTHING taking place
The Nature of Liquids A liquid will evaporate faster when heated Because the added heat increases the average kinetic energy needed to overcome the attractive forces so more particles have enough energy to escape! But, evaporation is a COOLING process Cooling occurs because particles with the highest energy escape first
The Nature of Liquids Particles left behind have lower average kinetic energies; thus the temperature decreases Similar to removing the fastest runner from a race the remaining runners have a lower average speed Evaporation helps to keep our skin cooler on a hot day, unless it is very humid on that day. Why?
The Nature of Liquids A liquid boils when its vapor pressure equals the external pressure, so the boiling point changes if the external pressure changes. Bubbles form throughout the liquid, rise to the surface, and escape into the air Normal boiling point is when the vapor pressure of a liquid equals standard pressure. (1 atm)
The boiling point (bp) is the temperature at which the vapor pressure of the liquid is equal to the external pressure on the liquid
The Nature of Liquids Normal bp of water = 100 C However, in Denver = 95 C, since Denver is 1600 m above sea level and average atmospheric pressure is about 85.3 kpa (Recipe adjustments?) In pressure cookers, which reduce cooking time, water boils above 100 C due to the increased pressure
Vapor Pressures of Liquids Normal bp when crossing here At any pt. on a curve line, liquid is boiling
SOLIDS If you cool a liquid, the particles lose kinetic energy and slow down & get closer together. If they slow down enough, extra forces of attraction pull them in so close together that they can only vibrate in place. Freezing change of a liquid to a solid.
WHAT ARE ICE SPIKES? Ice spikes grow as the water in an ice cube tray turns to ice. The water first freezes on the top surface, around the edges of what will become the ice cube. The ice slowly freezes in from the edges, until just a small hole is left unfrozen in the surface. At the same time, while the surface is freezing, more ice starts to form around the sides of the cube. Since ice expands as it freezes, the ice freezing below the surface starts to push water up through the hole in the surface ice (see diagram). If the conditions are just right, then water will be forced out of the hole in the ice and it will freeze into an ice spike, a bit like lava pouring out of a hole in the ground to makes a volcano. But water does not flow down the sides of a thin spike, so in that way it is different from a volcano. Rather, the water freezes around the rim of the tube, and thus adds to its length. The spike can continue growing taller until all the water freezes, cutting off the supply, or until the tube freezes shut.
Types of CRYSTALLINE Solids Molecular solids Metallic solids Ionic solids Covalent network solids
Homework On the L side of the notes: What is the Kinetic Molecular Theory?
MOLECULAR SOLIDS These types of crystalline solids have molecules at the corners of the lattice instead of individual ions. They are softer, less reactive, have weaker non polar ion attractions, and lower melting points. A molecular solid is held together by intermolecular forces. The bonding of hydrogen and oxygen in frozen water shows how hydrogen forms bonds between different water molecules.
METALLIC SOLIDS Another type of crystalline solid is made up of metals.
IONIC SOLID Ionic solids form a lattice with the outside points made up of ions instead of larger molecules. These are the opposites attract solids.
COVALENT SOLIDS A grouping of covalent bonds holds some solids together. Assembled together in large nets or chains, covalent multi layered solids are extremely hard and stable in this type of configuration
What is a Crystalline Solid? Particles of crystals are arranged in repeating geometric patterns
Crystalline Solids
Table salt crystals are shaped like cubes.
Diamond, a form of carbon, is also a crystalline solid the crystals are shaped something like pyramids.
Non-crystalline solids Solids that do not form crystals (Amorphous) Their molecules do not arrange into repeating patterns often because they are too large Examples: Glass also called a super cooled liquid many plastics, soot, asphalt, butter
PHASE CHANGES PHASE CHANGES change is physical state (melting, freezing, boiling, condensing, sublimation, deposition) BOTH PHASES are present during a phase change Temperature remains constant during a phase change. Sublimation change of a solid directly to a gas (dry ice, iodine, snow) Deposition change of a gas directly to a solid. Phase Diagrams show relationship between energy, temperature, & phases.
60 20 0-20 0 Heat (kilojoules) Temperature (C )
Phase Diagram Freezing/ Melting occur along this line Boiling/condensing occur along this line Unless told otherwise, read the pressure at standard pressure water Sublimation/deposition occur along this line