Chapter 8 Those incredible water molecules
Water is the most important substance on earth
and in any living organism,Why?
8.1 Water molecules form an open crystalline
structure in ice
When water freezes,the water molecules arrange themselves in a
six-sided crystalline structure.
Increased structural orderliness usually means increased density.
Solids and crystals have high structural orderliness and are thus
denser than liquid and non-crystalline materials,But water is
exception.
8.2 Freezing and melting go on at the same
time
Hydrogen bonds form during freezing of water,releasing heat.
They break during melting,absorbing heat.
Adding salt to water decreases the melting point of water.
Water is densest at 4℃
When the temperature of
a given is increased,
its molecules vibrate
faster and move
farther apart,So the
substance expands.
This is the case in all
three phases of water,
apart from the liquid
water from 0-4℃, The
reason is,ice-like”
crystal structure starts
to form at 4℃,
The fact that water is densest at 4℃ is of great
importance in nature
8.3 The behavior of liquid water is the result
of the stickness of water molecules
Cohesive force ( 内聚力 ),forces of
attraction between molecules of a
single substance.
Adhesive force ( 粘合力 ),forces of
attraction between molecules of two
different substances.
Coin resting on the water surface,Why?
Surface tension (表面张力 )
Surface tension ( 表 面 张 力 ),The
tendency of the molecules on the
surface of a liquid to go into the
liquid,The surface tension also
accounts for the spherical shape of
liquid drops,especially in the
weightless environment.
Water has very high surface tension because of the strong hydrogen
bond,which prevents it from wetting materials with nonpolar
surfaces,such as waxy leaves,umbrellas,The addition of
detergent (or) soap can reduce the surface tension and increase
the wettability of water.
Capillary action (毛细管作用 ) results from the interplay
of adhesive and cohesive forces
8.4 Water molecules move freely between the
liquid and gaseous phases
Evaporation (蒸发 ) is a cooling
process,Condensation (凝聚 )
is a warming process.
A large amount of energy is
released during the
condensation of water vapor.
Household radiator
Hurricanes (The formation of 1
inch of rain over an area of 1
square mile yields the energy
equivalent of about 32000
tons of exploded dynamite.)
Boiling is evaporation beneath a liquid surface
8.5 It takes a lot of energy to change the
temperature of water
Water has a very high specific heat capacity (热容 ) because of
the strong hydrogen bond.
Specific heat capacity is defined as the quantity of heat required
to change the temperature of 1 gram of substance by 1℃,
Global climates are influenced by water’s high specific
heat capacity.
8.6 A phase change requires the input or output of
energy
Any phase change involves the breaking or forming of molecular
attraction and thus the release or absorption of energy.
Solid to liquid,heat of melting (positive,increase the potential energy)
Liquid to solid,heat of freezing (negative,reduce the potential energy)
Liquid to gas,heat of vaporization (positive)
Gas to liquid,heat of condensation (negative)
Summarization
Water is the most important substance on earth
and in any living organism,Why?
8.1 Water molecules form an open crystalline
structure in ice
When water freezes,the water molecules arrange themselves in a
six-sided crystalline structure.
Increased structural orderliness usually means increased density.
Solids and crystals have high structural orderliness and are thus
denser than liquid and non-crystalline materials,But water is
exception.
8.2 Freezing and melting go on at the same
time
Hydrogen bonds form during freezing of water,releasing heat.
They break during melting,absorbing heat.
Adding salt to water decreases the melting point of water.
Water is densest at 4℃
When the temperature of
a given is increased,
its molecules vibrate
faster and move
farther apart,So the
substance expands.
This is the case in all
three phases of water,
apart from the liquid
water from 0-4℃, The
reason is,ice-like”
crystal structure starts
to form at 4℃,
The fact that water is densest at 4℃ is of great
importance in nature
8.3 The behavior of liquid water is the result
of the stickness of water molecules
Cohesive force ( 内聚力 ),forces of
attraction between molecules of a
single substance.
Adhesive force ( 粘合力 ),forces of
attraction between molecules of two
different substances.
Coin resting on the water surface,Why?
Surface tension (表面张力 )
Surface tension ( 表 面 张 力 ),The
tendency of the molecules on the
surface of a liquid to go into the
liquid,The surface tension also
accounts for the spherical shape of
liquid drops,especially in the
weightless environment.
Water has very high surface tension because of the strong hydrogen
bond,which prevents it from wetting materials with nonpolar
surfaces,such as waxy leaves,umbrellas,The addition of
detergent (or) soap can reduce the surface tension and increase
the wettability of water.
Capillary action (毛细管作用 ) results from the interplay
of adhesive and cohesive forces
8.4 Water molecules move freely between the
liquid and gaseous phases
Evaporation (蒸发 ) is a cooling
process,Condensation (凝聚 )
is a warming process.
A large amount of energy is
released during the
condensation of water vapor.
Household radiator
Hurricanes (The formation of 1
inch of rain over an area of 1
square mile yields the energy
equivalent of about 32000
tons of exploded dynamite.)
Boiling is evaporation beneath a liquid surface
8.5 It takes a lot of energy to change the
temperature of water
Water has a very high specific heat capacity (热容 ) because of
the strong hydrogen bond.
Specific heat capacity is defined as the quantity of heat required
to change the temperature of 1 gram of substance by 1℃,
Global climates are influenced by water’s high specific
heat capacity.
8.6 A phase change requires the input or output of
energy
Any phase change involves the breaking or forming of molecular
attraction and thus the release or absorption of energy.
Solid to liquid,heat of melting (positive,increase the potential energy)
Liquid to solid,heat of freezing (negative,reduce the potential energy)
Liquid to gas,heat of vaporization (positive)
Gas to liquid,heat of condensation (negative)
Summarization
