Properties of waterAquatic Ecology82504 - PowerPoint PPT Presentation

Title: Properties of waterAquatic Ecology82504


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Properties of water/Aquatic Ecology/8-25-04
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CHEMICAL AND PHYSICAL PROPERTIES OF WATER
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We already know that matter comes in different
forms
Solids are formed when the attraction between
individual molecules is greater than the energy
causing them to move apart
Liquids are formed when energy (usually heat) in
a system is increased and the rigid structure of
the solid state is broken down
Gases are formed when the energy in the system
exceeds the attraction between molecules. In a
gaseous state, molecules move quickly and are
free to move in any direction
One of the many unusual properties of water is
that it exists in liquid form at normal
atmospheric temperature and pressures encountered
on the surface of the earth.
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Water has a very simple atomic structure two
hydrogen atoms bonded to one oxygen atom
The hydrogen side of the water molecule has a
slight positive charge - and on the oxygen side
there is a negative charge
This molecular polarity causes water to be a
powerful solvent and is responsible for it strong
surface tension
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• Solvent a liquid that dissolves a solute.
• A substance is soluble if it dissolves in
  certain fluids
• Together the solute and solvent form a solution
• The solvent is the component of a solution that
  is present in a greater amount

Surface tension - tension of a liquids surface.
Due to the forces of attraction between molecules
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• The attraction created by hydrogen bonds keeps
  water liquid over a wider range of temperature
  than is found for any other molecule its size

• The energy required to break multiple hydrogen
  bonds causes water to have a high heat of
  vaporization a large amount of energy is needed
  to convert liquid water to water vapor

• The hydrogen bond has only 5 of the strength
  of a covalent bond. However, when many hydrogen
  bonds can form between two molecules, the
  resulting bonds can be sufficiently strong to be
  stable.

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Covalent bond chemical bond between two atoms
in which electrons are shared in water each of
the covalent bonds contains tow electrons one
from the hydrogen atom and one from the oxygen
atom. Both atoms share the electrons.
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• Water has several other unique physical
  properties
• High specific heat
• Neutral pH
• Conducts heat more easily than any liquid except
  mercury
• Water exists as a liquid over an important range
  of temperatures 0 1000C
• Liquid water is a universal solvent

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The freezing of water causes it to expand. When
water freezes it expands rapidly adding about 9
by volume. Fresh water has a maximum density at
around 40C. Water is the only substance on this
planet where the maximum density of its mass does
not occur when it becomes solidified.
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Phase Changes If heat were added at a constant
rate to a mass of ice to take it through its
phase changes to liquid water and then to steam,
the energies required to accomplish the phase
changes (latent heat of fusion and heat of
vaporization) would lead to plateaus in the
temperature vs time.
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Heat of Fusion The energy required to change a
gram of a substance from the solid to the liquid
state without changing its temperature. This
energy breaks down solid bonds, but leaves a
significant amount of energy associated with the
intermolecular forces of the liquid state.
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Heat of Vaporization The energy required to
change a gram of liquid into the gaseous state at
the boiling point. This energy breaks down the
intermolecular attractive forces, and also must
provide the energy necessary to expand the gas.
The final energy is depicted here as being in
translational kinetic energy, which is not
strictly true. There is also some vibrational and
rotational energy
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Fig. 10.13
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Energy is defined as the ability to do work
Work is defined as the transfer of energy
Kinetic energy when something is in motion it
is said to have kinetic energy
The water in this flood possesses kinetic energy
since it is moving. It gets this energy because
it is falling through a gravitational field. As
it falls, energy in the gravitational field comes
out of storage and is used to move the water.
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RELATIONSHIPS AMONG WATER
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Surface Water
Shortages 30 maximum withdrawal Gallons
used/day/person 150
Ecological Effects A. Wetlands dry up eg.
Everglades B. Estuaries are destroyed less
fresh water flushing therefore more salt water
Overuse of Groundwater 1. Falling Water
Tables 2. water from spring stops 3. Land
Subsidence sinkholes, salt water intrusion
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CONSERVATION OF WATER
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Irrigation 85 of water is used in
irrigation. 50 is wasted. most crops grown are
in huge surpluses Drip irrigation as a solution
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Municipal System 1. 150 gal. Of
water/person/day Is it necessary??? 2.water
conservation Gray Water Recycling
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Effects Caused by Changing Land Use.
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• Watershed all the land from which water drains
  into a stream or river. Eg. Wissahickon Watershed
• Natural land allows rain to infiltrate into
  ground water recharge the groundwater.
• Paving land, housing, even lawns can cause too
  much runoff.

• Effects of Increasing Runoff
• Stream bank erosion
• Flooding
• Increased pollution

• Effects of decreased Infiltration
• Groundwater is not discharged
• Water Table drops

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Storm Water Management (preventing Runoff) -Dry
well trenches -Barriers - parking Lots -
retention Ponds

• Implementing Solutions
• -Stormwater management
• -make water expensive