Liquids and Solids

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Liquids and Solids

• Chapter 14

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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)
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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)
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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
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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.
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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 Boiling Point
Normal freezing point
1.00 g 0.917 1.00g 1.09 ml ICE
1.00 ml
Heating/Cooling curve simulation
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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.

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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.

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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.

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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.

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14.4 Evaporation and Vapor Pressure

• Objective To understand the relationship among
  vaporization, condensation and vapor pressure.

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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.
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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

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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 evaporatethe of
condensation. EQUILIBRIUM
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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 forcesrelatively
low vapor pressure Because such molecules need
high energy to escape to the vapor phase.
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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
HF because although hydrogen bonding occurs in
both samples, water has 2 OH bonds that
are capable of hydrogen bonding
H2O(l) or HF (l)
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.
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14.5 Boiling Point and Vapor Pressure

• Objective To relate the boiling point of water
  to its vapor pressure.

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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.
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14.5 Boiling Point and Vapor Pressure
What happens to the temperature that water boils
above sea level?
Feet above sea level Patm BP Mt. Everest
29,028 0.32 70 Boulder, CO 5430 0.80 94 Madis
on, WI 900 0.96 99 NYC, NY 10 1.00 100 Death
Valley -282 1.01 100.3
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14.5 Boiling Point and Vapor Pressure
Which has the higher boiling point? H2O or
CH4 C2H6 or C6H14
H2O
C6H14
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14.6 The Solid State Types of Solids

• Objective To learn about the various types of
  crystalline solilds.

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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
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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.

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14.7 Bonding in Solids

• Ionic solids
• High melting points

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14.7 Bonding in Solids
Molecular Solids Melt at relatively low
temperatures because the intermolecular forces
are relatively weak.
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14.7 Bonding in Solids
Atomic solidsProperties vary greatly
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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.