Download Chapter 12 - Midway ISD

Chapter 12
Liquids and Solids
Sect. 12-1: Liquids
Properties of liquids
Definite volume
Takes shape of its container
Properties can be explained by the kinetic
molecular theory (KMT) just like gases were
explained
Fluid – has the ability to flow
Properties of liquids (con’t)
Relatively high density
Relative incompressibility
Ability to diffuse
Surface tension – force that tends to pull
adjacent parts of a liquid’s surface
together, thereby decreasing surface area
to the smallest possible size
More properties of liquids…
Capillary action – the attraction of the
surface of a liquid to the surface of a solid
Vaporization – liquid changes to a gas
Evaporation – vaporization occurring at
the surface of a non-boiling liquid
Freezing – liquid changing to a solid
Sect. 12-2: Solids
Properties of solids
Definite volume
Definite shape
Properties can be explained by the kinetic
molecular theory (KMT) just like gases and
liquids were explained
Two types of solids
Crystalline solids – made up of crystals
Crystals – particles are arranged in an orderly,
geometric fashion
Amorphous solids – particles are arranged
randomly
More properties of solids…
Definite melting point – temperature at
which a crystalline solid turns into a liquid
Supercooled liquids – substances that
retain certain liquid properties even at
temperatures at which they appear to be
solid (amorphous solids)
High density
Incompressibility
Very low rate of diffusion
Crystalline solids
Crystal structure – total 3D arrangement of
particles of a crystal
Unit cell – smallest part of a crystal
structure that shows the 3D pattern of the
entire structure
Binding forces in crystals
Ionic crystals
Covalent network crystals
Metallic crystals
Covalent molecular crystals
Sect.12-3: Changes of State
Equilibrium – a dynamic condition in which
two opposing changes occur at equal
rates in a closed system
Phase – any part of a system that has
uniform composition and properties
Equilibrium and changes of state
If you start out with a closed container of
liquid, eventually some of it will evaporate.
Over time, some of the gas will condense.
If left for a long enough period of time,
equilibrium will be reached for amount of
substance condensing vs. evaporating.
Represented by the following equation:
liquid + heat energy  vapor
System will stay at equilibrium until some
outside force acts upon it.
Le Châtelier’s Principle – when a system
at equilibrium is disturbed by an
application of stress, it attains a new
equilibrium position that minimizes the
stress
Stress is typically a change in concentration,
pressure, or temperature.
Equilibrium and temperature
What will happen to earlier discussed
liquid/vapor system if temperature is
increased? Which reaction will be
favored?
What if temp is decreased? Which
reaction is favored?
Equilibrium and concentration
 What would happen to system if volume of
container was suddenly increased?
 Amount of vapor would now be in lower
concentration and thus less condensation would
be occurring and more evaporation occurring
until system reaches equilibrium again.
 At the new equilibrium, there fewer liquid
molecules, but the same concentration of the
gas due to larger container size. (equilibrium has
shifted right)
Equilibrium and Vapor Pressure of Liquid
Equilibrium vapor pressure – pressure
exerted by a vapor in equilibrium over a
liquid at a given temperature (increases as
temp increases)
Explained by KMT
Pg. 376 for illustration
Volatile vs. nonvolatile liquids
Volatile liquid – liquids which evaporate
very easily due to weak forces of attraction
between particles
Have a relatively high equilibrium vapor
pressure
Nonvolatile liquids have stronger forces of
attraction and lower equilibrium vapor
pressures
Boiling
Boiling – conversion of a liquid to a gas at
the surface and throughout the liquid
Boiling point – temperature at which the
equilibrium vapor pressure is equal to the
atmospheric pressure
Pressure affects the boiling point
Normal boiling point is at 1 atm pressure
During a phase change, such as
vaporization, the temperature remains
constant because any heat being added is
going to changing the particles from liquid
to gas
Molar heat of vaporization – amount of
heat required to vaporize one mole of
liquid at its boiling point
The higher it is, the stronger the bonds are that
hold that liquid together
Freezing and Melting
Freezing point – temperature at which the
solid and liquid are in equilibrium at 1 atm
Molar heat of fusion – amount of heat
required to melt one mole of a solid at its
melting point
Sublimation – change of state from a solid
directly to a gas
Deposition – change of state from a gas
directly to a solid
Both occur at low pressures and
temperatures where a liquid cannot exist
Phase Diagrams
Phase diagram – a graph of pressure vs.
temperature that shows the conditions
under which the phases of a substance
exist
Triple point – indicates the temperature
and pressure at which the solid, liquid, and
vapor can coexist at equilibrium
Critical point – indicates critical temp. and
pressure
Critical temperature (tc)– temp above
which a substance cannot exist as a liquid
Critical pressure (Pc) – lowest pressure at
which the substance can exist as a liquid
at the critical temperature
Sect. 12-4: Water
 Water molecules have
a bent structure
 Solid or liquid water
molecules are linked
by hydrogen bonding
 Ice is made up of
water arranged in
hexagon shapes; this
allows for low density
Physical Properties of Water
Liquid water is odorless, tasteless, &
transparent
Relatively high molar heat of fusion (6.009
kJ/mol)
Relatively high boiling point and molar
heat of vaporization (40.79 kJ/mol)
compared to other substances that have
similar molar masses (because of
hydrogen bonding)