Chemistry chapter 12 2
Liquid
Has a definite volume and indefinite shape
Particles are in constant motion Closer together than gases Less kinetic energy than gases Greater attractive forces than gases
Chemistry chapter 12 4
Fluid density
At normal pressure, most liquids are thousands of times denser than their gases. Particles are closer together
Different liquids can vary greatly in density
Chemistry chapter 12 6
Incompressibility
Liquids are much less compressible than gases Particles are closer together Liquids can transmit pressure
throughout themselves
Chemistry chapter 12 7
Diffusion Liquids diffuse in other liquids in
which they can dissolve Much slower than gases
Particles closer together Attraction between particles slows
them down Faster at higher temperatures
More kinetic energy
Chemistry chapter 12 8
Surface Tension
Force that pulls parts of a liquid’s surface together, causing it to have the smallest possible size
From attractive forces between molecules
Liquid droplets take a spherical shape
Chemistry chapter 12 9
Capillary action
The attraction of the surface of a liquid to the surface of a solid Causes meniscus Water can travel up paper Water traveling up a plant Drawing blood in capillary tube
Chemistry chapter 12 10
Vaporization
Changing from a liquid to a gas Evaporation
Higher energy particles escape from the surface of a nonboiling liquid
perfume
Boiling Bubbles of vapor that appear
throughout the liquid and travel to the surface
Chemistry chapter 12 11
Freezing
Changing a liquid to a solid by removing heat
Energy of particles decreases until they are pulled into a more orderly arrangement
Chemistry chapter 12 12
Discussion
Describe the liquid state using kinetic molecular theory.
Explain why liquids in a test tube form a meniscus.
Compare and contrast vaporization and evaporation.
Chemistry chapter 12 13
Solid
Has definite volume and definite shape
Particles are in constant motion Much closer together than liquid or
gas Much stronger intermolecular forces Held in relatively fixed position – only
vibrate Most ordered state of matter
Chemistry chapter 12 14
High density and incompressibility
Substances are generally the most dense in the solid state Slightly denser than liquids, much
denser than gases Virtually incompressible
Sometimes we compress air pockets in the solids
Wood, cork, etc.
Chemistry chapter 12 15
Diffusion
Very, very slow A few atoms may diffuse if
clamped together for a long time
Chemistry chapter 12 16
Melting
Change of a solid to a liquid by addition of heat
Melting point – temperature at which something melts
Chemistry chapter 12 17
Crystalline solids
Consist of crystals Particles are arranged in an orderly,
geometric, repeating pattern Fragments have geometric shapes Have definite melting points
When the crystal structure breaks apart
Chemistry chapter 12 18
Crystal structure
Total three-dimensional arrangement of particles in a crystal
Chemistry chapter 12 19
Lattice
Coordinate system that represents the arrangement of particles in a crystal.
Chemistry chapter 12 20
Unit cell
Smallest portion of a crystal lattice that shows the 3D pattern of the entire lattice
Each crystal lattice contains many unit cells packed together
Has one of seven types of symmetry – see page 369
Chemistry chapter 12 21
Ionic crystals
Positive and negative ions in a regular pattern
Hard and brittle High melting points Good insulators
Chemistry chapter 12 22
Covalent network crystals Individual atoms connected by
covalent bonds Giant molecules
Diamond Quartz
Very hard and brittle Rather high melting points Nonconductors or semiconductors
Chemistry chapter 12 23
Metallic crystals
Metal atoms surrounded by a sea of electrons
High electrical conductivity Varying melting points
Chemistry chapter 12 24
Covalent molecular crystals
Covalently bonded molecules held together by intermolecular forces
Low melting points Easily vaporized Relatively soft Good insulators
Chemistry chapter 12 25
Amorphous solids
Noncrystalline solids The particles are arranged
randomly Glass Plastics
Can be molded Fragments have irregular shapes
Chemistry chapter 12 26
Amorphous solids
Made by cooling molten substances in a way that prevents crystallization
Also called supercooled fluids Retain certain fluid characteristics
even at temperatures at which they appear to be solid
Can flow over a wide range of temperatures
Chemistry chapter 12 27
Discuss
Account for each of the following properties of solids: Definite volume Relatively high density Extremely low rate of diffusion
What is the difference between an amorphous solid and a crystalline solid?
Chemistry chapter 12 28
Possible changes of state
Melting: solid to liquid Sublimation: solid to gas Freezing: liquid to solid Vaporization: liquid to gas Condensation: gas to liquid Deposition: gas to solid
Chemistry chapter 12 30
Equilibrium
A dynamic condition in which two opposing changes occur at equal rates in a closed system.
The same number of particles are entering and leaving.
The total number stays the same.
Chemistry chapter 12 32
Phase
Any part of a system that has uniform composition and properties. Liquid or gas
Chemistry chapter 12 33
An Equilibrium equation
When a substance changes state, it either absorbs or gives off energy, usually as heat.
vaporenergy heat liquid
Chemistry chapter 12 34
Le Châtelier’s Principle
A system remains in equilibrium until a stress occurs on the system. Stress: change in concentration,
pressure, or temperature When a system is disturbed by a
stress, it attains a new equilibrium position that minimizes the stress.
Chemistry chapter 12 35
Shifting equilibrium
Shifts to the right or left, depending on which part of the equation gains concentration.
See table 12-3 on page 375
Chemistry chapter 12 36
Equilibrium vapor pressure
The pressure exerted by a vapor in equilibrium with its liquid at a given temperature
Increases as temperature increases But not directly
Chemistry chapter 12 37
Kinetic-molecular theory
Increasing the temperature increases the energy and speed of the liquid particles
This means more particles evaporate, leading to higher vapor pressure
Chemistry chapter 12 38
Caution
Equilibrium vapor pressure depends only on temperature.
If the system is not in equilibrium, gas laws must be used.
Chemistry chapter 12 39
Volatile liquids
Evaporate easily Weak forces of attraction between
particles Ether, acetone
Chemistry chapter 12 40
Boiling
Conversion of a liquid to a vapor within the liquid as well as at the surface.
Occurs when the equilibrium vapor pressure equals atmospheric pressure.
All the heat absorbed goes to evaporate the liquid, so the temperature remains constant.
Chemistry chapter 12 42
Cooking If atmospheric pressure is lower (high
altitudes), liquids boil at lower temperatures and food takes longer to cook.
If the pressure is increased (pressure cooker), liquids boil at higher temperatures and food cooks faster.
If the pressure is decreased, it boils at low enough temperatures to avoid scorching milk and sugar. (evaporated and sweetened condensed milk)
Chemistry chapter 12 43
Molar heat of vaporization
The amount of energy needed to vaporize one mole of liquid at its boiling point. (or the amount of energy released
when one mole of vapor condenses) A measure of the attraction
between particles.
Chemistry chapter 12 44
Normal freezing point
Temperature at which the solid and liquid are in equilibrium at 1 atm pressure.
When a liquid freezes, energy is lost and order is gained.
Chemistry chapter 12 45
Clarification
Boiling point is the same as condensation point.
Freezing point is the same as melting point.
Chemistry chapter 12 46
Molar heat of fusion
The amount of heat energy required to melt one mole of solid at its melting point (or the amount of energy released
when one mole of a liquid freezes) Depends on the attraction between
particles.
Chemistry chapter 12 47
Phase diagram
A graph of pressure versus temperature that shows the conditions under which the phases of a substance exist
Reveals how the states of a system change with changes in temperature or pressure
Chemistry chapter 12 49
Curves on diagram
AB shows where solid and vapor can exist at equilibrium
AC shows liquid and vapor at equilibrium
AD shows solid and liquid at equilibrium Usually a positive slope, but water is
different
Chemistry chapter 12 50
Triple point
Point A Shows the temperature and
pressure at which solid, liquid, and vapor can exist in equilibrium
Chemistry chapter 12 51
Critical temperature
Temperature above which the substance cannot exist in the liquid state.
Chemistry chapter 12 52
Critical pressure
The lowest pressure at which the substance can exist as a liquid at the critical temperature
Chemistry chapter 12 57
Water Bent molecule
Bond angle = 105° Hydrogen bonding in liquids and
solids Usually 4 – 8 molecules per group in
liquid water Without them, water would be a gas at
room temperature Ice has hexagonal arrangement
Empty spaces lead to low density
Chemistry chapter 12 58
Water
Has highest density at 3.98 °C When it melts, molecules can crowd
together When it gets hotter, increased kinetic
energy makes them spread apart Needs a lot of energy to
completely break hydrogen bonds and vaporize
Chemistry chapter 12 59
Water Pure liquid water is transparent,
odorless, tasteless, and almost colorless Odors or tastes are caused by impurities
Molar heat of fusion: 6.009 kJ/mol Relatively large Density of ice: 0.917 g/cm3
Molar heat of vaporization: 40.79 kJ/mol Quite high
Chemistry chapter 12 60
Calculating heat energy
energyheat ation or vaporizfusion ofheat amount
kJmol
kJmol
Chemistry chapter 12 61
Example
Find the mass of liquid water required to absorb 5.23 x 104 kJ of heat energy on boiling.
2.31 x 104 g
Chemistry chapter 12 63
You try
Calculate the quantity of heat energy released when 783 g of steam condenses.
1.77 x 103 kJ