Transcript Liquids and Solids

Liquids and Solids
Chapter 14
14.1 Intermolecular Forces
• Most small molecules are a gas at room
temperature (Examples: O2, NH3)
Water is a liquid…..WHY????
INTERMOLECULAR FORCES
DIPOLE-DIPOLE ATTRACTIONS: can attract each other
by lining up so that the positive/negative ends are close
1% as strong as covalent or ionic bonds. (NOT IMPT. In gases)
HYDROGEN BONDING is impt. Strong dipole-dipole
H bound to highly electronegative atom (N, F, O)
14.1 Intermolecular Forces
DIPOLE-DIPOLE ATTRACTIONS: can attract each other
by lining up so that the positive/negative ends are close
1% as strong as covalent or ionic bonds. (NOT IMPT. In gases)
HYDROGEN BONDING is impt. Strong dipole-dipole
H bound to highly electronegative atom (N, F, O)
14.1 Intermolecular Forces
HYDROGEN BONDING is impt. Strong dipole-dipole
H bound to highly electronegative atom (N, F, O)
H Bonding
IMPT. Effect
on physical
properties
Boiling point for water is much higher
than would be expected from the trend shown by the
other members of the series.
O-H more polar than the others
14.1 Intermolecular Forces
London Dispersion Forces:
forces that exist among
noble gas atoms and
nonpolar molecules.
-Atoms can temporarily
develop a dipole
-This instantaneous
dipole can then induce a
similar dipole in a
neighboring atom.
The motions of the atoms must be greatly slowed down
before the weak dispersion forces can lock the atoms into place
to produce a solid.
14.2 Water and Its Phase Changes
HEATING/COOLING CURVE FOR WATER
Water expands
when it freezes.
When one gram of
water freezes, its volume
becomes greater.
The density of one gram
of ice is less than the
density of one gram of
water.
Normal freezing point
1.00 g = 0.917
1.00g
1.09 ml
ICE
1.00 ml
Heating/Cooling curve simulation
Normal Boiling Point
14.3 Energy Requirements for the
Changes of State
Objectives: To learn about interactions
among water molecules.
To understand and use heat of fusion and
heat of vaporization.
14.3 Energy Requirements for the
Changes of State
Molar heat of fusion: For ice, the molar heat
of fusion is 6.02 kJ/mol. (melting)
Molar heat of vaporization: For water, 40.6
kJ/mol at 100oC.
14.3 Energy Requirements for the
Changes of State
Calculate the energy required to vaporize
35.0 g of water at 100oC. The molar heat
of vaporization of water is 40.6 kJ/mol.
14.3 Energy Requirements for the
Changes of State
Calculate the energy required to vaporize
22.5 g of water at 0oC and change it to
steam at 100oC. The specific heat
capacity of liquid water is 4.18 J/goC and
the molar heat of vaporization of water is
40.6 kJ/mol.
14.4 Evaporation and Vapor
Pressure
Objective: To understand the relationship
among vaporization, condensation and
vapor pressure.
14.4 Evaporation and Vapor
Pressure
Vaporization (Evaporation): requires energy to
overcome the relatively strong intermolecular
forces in the liquid
A given component must have
sufficient speed to overcome
the intermolecular forces.
14.4 Evaporation and Vapor
Pressure
As vaporization occurs the remaining
particles have a lower kinetic energy,
lower temperature (insulated container) or
remains constant if heat is flowing in,
THUS
Evaporation is endothermic
14.4 Evaporation and Vapor
Pressure
Condensation: the process by which
vapor molecules form a liquid.
The volume initially decreases…
Eventually, this stops as the # of
molecules that evaporate=the #
of condensation.
EQUILIBRIUM
The pressure of the vapor present
at equilibrium with its liquid is called
the equilibrium vapor pressure
The vapor pressure of a liquid at a given temperature is determined by the
Intermolecular forces. Large intermolecular forces=relatively low vapor pressure
Because such molecules need high energy to escape to the vapor phase.
14.4 Evaporation and Vapor
Pressure
Predict which substance in each of the following pairs will show
the largest vapor pressure at a given temperature
H2O(l) or HF (l)
HF because although hydrogen bonding occurs
in both samples, water has 2 OH bonds that are
capable of hydrogen bonding
CH3OCH3(l) or CH3CH2OH(l)
CH3OCH3. No hydrogen bonding can exist
in this molecule because the hydrogen atoms
are attached to carbon atoms, not the oxygen
atoms.
14.5 Boiling Point and Vapor
Pressure
Objective: To relate the boiling point of water to its
vapor pressure.
14.5 Boiling Point and Vapor
Pressure
Bubbles expand when high-energy water molecules enter the bubble
And produce enough internal pressure to push back the water
Surrounding the bubble.
The vapor pressure of the water must = the atmospheric pressure before boiling.
14.5 Boiling Point and Vapor
Pressure
What happens to the temperature that water boils above sea level?
Mt. Everest
Boulder, CO
Madison, WI
NYC, NY
Death Valley
Feet above sea level
29,028
5430
900
10
-282
Patm
0.32
0.80
0.96
1.00
1.01
BP
70
94
99
100
100.3
14.5 Boiling Point and Vapor
Pressure
Which has the higher boiling point?
H2O or CH4
C2H6 or C6H14
H2O
C6H14
14.6 The Solid State: Types of
Solids
Objective: To learn about the various types
of crystalline solilds.
14.6 The Solid State: Types of
Solids
Crystalline solids: solids with a regular arrangement of their
components
The properties of a solid
are determined primarily
by the nature of the forces
that hold the solid together
14.7 Bonding in Solids
Objective: To understand the interparticle
forces in crystalline solids.
To learn about how the bonding in metals
determines metallic properties.
14.7 Bonding in Solids
Ionic solids:
High melting points
14.7 Bonding in Solids
Molecular Solids: Melt at relatively low temperatures because the intermolecular
forces are relatively weak.
14.7 Bonding in Solids
Atomic solids:Properties vary greatly
14.7 Bonding in Solids
Bonding in Metals: Strong but not directional. Difficult
To separate but they can slide past each other.
Substitutional alloy: host metal atoms are replaced by
other metal atoms.
Interstitial alloy: formed when some of the holes are filled
with another atom.