Surface
Tension
Colour
Cohesion
Properties of Water
WJEC GCE BIOLOGY
Latent
heat
State at
room
temp.
Specific
heat
capacity
Density
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Properties of Water
WJEC GCE BIOLOGY
Surface Tension
• The surface of water can behave
like an elastic sheet
• The molecules in the bulk of the
liquid are effected by various
intermolecular forces of
attraction
• Those molecules in the surface
are not effected by molecules
above them, and therefore ‘pull’
together more strongly,
effectively resembling a
stretched membrane
• A habitat can therefore survive
on the surface of the water
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Colour – transmission of light
• Water is colourless and is
therefore transparent to light
• This means that sunlight can
reach the cells and pass through
them so that photosynthesis may
occur
Reflected by leaves
53%
10%
13%
Properties of Water
WJEC GCE BIOLOGY
Sun light
Light absorbed by leaves
(typical values):
Near IR 15%
Red 82%
Green 80%
Blue 84%
9%
8%
7%
7%
32%
Transmitted through
leaves
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Cohesion
• Water molecules show a strong
attraction to one another, this is
called cohesion.
Properties of Water
WJEC GCE BIOLOGY
Droplets of water
form spheres due to
cohesion between
water molecules
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Latent heat
•
While changing state, a substance will take
in heat energy (solid  liquid  gas), or
expel heat energy (gas  liquid  solid)
without a change in temperature. This is
termed Latent Heat.
temperature
evaporate
GAS
condense
Properties of Water
WJEC GCE BIOLOGY
•
melt
Water has a large latent heat
of vaporisation, and therefore
absorbs a large amount of
heat energy while changing
from water to vapour.
solidify
time
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State at room temperature
•
Water is a liquid at room temperature.
This strange since all other similar
molecules are gases at this
temperature.
H
H
O
Properties of Water
WJEC GCE BIOLOGY
H
O
H
H
H
O
H
O
H
• Hydrogen bonds act
between the water
molecules, and they
attract them enough so
that it behaves as a liquid.
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Specific Heat Capacity
•
The heat needed to raise the
temperature of 1kg of water by 1°C is
termed the Specific Heat Capacity.
• Water has a large specific heat
capacity, and therefore can
absorb large amounts of heat
energy before its temperature
raises a significant amount.
Properties of Water
WJEC GCE BIOLOGY
thermometer
1kg of water
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Density of water
•
Unlike other substances, water
expands as it freezes.
H
Ice
Water
H
H
O
H
O
H
H
O
H
O
H
H
O
H
Properties of Water
H
H
H
Water molecules are able to
approach one another quite
closely
WJEC GCE BIOLOGY
O
H
H
O
H
O
O
Water molecules in ice form
a rigid structure so that there
is more space between
them, this is seen as
expansion as a whole
H
H
H
H
O
O
H
H
• As water expands when it
freezes, its density (mass per
unit volume) will decrease.
• This means that ice is less dense
than water, and will therefore
float on top of it.
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