Water -

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Water - the Earths Coolant
Chapter 23 and 24
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Put this in your notes
The Earths energy is solar. Incident light
from the Sun heats the surface. Waters high
heat capacity allows it to absorb or give up
this energy without much temperature change.
Circulation in the ocean and atmosphere
redirects energy from regions of excess
(tropical zones to regions of deficit (polar
zones), moderating temperatures in both.
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Now, lets explain this process!
Water is the Mickey Mouse molecule
hydrogen has one proton() and one electron (-)
oxygen has 8 protons and 8 electrons
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Water is a polar molecule (one end is more
negative and the other is more positive).
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Why should I care??!!
H and O from different molecules form weak bonds
(hydrogen bonds) that make water a liquid.
Why do you think the polar nature allows this to
happen?
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The polar nature of water also makes it a VERY
good dissolver (THINK what do you do with a
really yucky pan- soak it overnight!)
This polar nature also makes water wet- it
adheres (sticks) well to things
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What else can we blame on waters polar nature?..
Waters ability to absorb heat energy without a
big rise in temperature! or give up heat without
a big drop in temperature)
Lets look at heat and temperature
( there is a difference, you know!)
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Heat is the energy of molecular vibration.
Temperature is a measure of that energy.
Solids have low enough energy that molecules can
form rigid bonds.
Gases have such high energies that the molecules
cannot form bonds.
Transitions between states take place by adding
or removing energy.
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Heat capacity is how much heat one gram of a
material can absorb before its temperature
changes by 1C.
Water has one of the highest heat capacities of
any known substance.
This is because the hydrogen bonds in liquid
water are strong enough that lots of heat
(vibrational) energy is required to break these
bonds, (and remember, the hydrogen bonds are a
consequence of the polar nature of water.
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This is why beaches are HOT and the surf is COOL!
even though both get the same solar heat.
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More weird properties of water.
Water is the only substance with a solid density
less than its liquid.
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E-D - all ice, adding heat raises temperature of
ice to 0C (melt point)
D-C - ice liquid water, constant T because all
heat going to melt ice
C-F - all liquid, heat raises temperature of
water by 1C for each calorie added per gram.
F-G - liquid vapor, water boiling, constant T
because heat added goes to breaking H bonds and
allowing molecules to escape (boil)
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Ice melting gives up almost as much heat energy
(80 calories) as it takes to raise the
temperature of 1 gram of water from freezing
temperature (0) to boiling (100C).
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.. and it takes over 5 times as much (540
calories) heat to boil a gram of water!
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Note Fog is NOT water vapor. It is made of
tiny droplets of liquid water that have
condensed in the atmosphere from vapor. This
vapor has given up its 540 cal/gram of energy to
form the droplets (warming the air).
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Why is this important to you?
1. In hot climates, evaporating water absorbs
LOTS of heat energy that could go to heating you
up! (the water in your perspiration gets some of
that energy from your skin, cooling you). TROPICS
2. In cold climates, freezing water gives up
heat to keep the air from getting any colder
than 0C. POLAR REGIONS
3. In your cold drink, melting ice absorbs heat
that could go to warming the liquid. This is why
your drink stays cold!
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But the ocean is NOT pure water. What is the
principal difference between water and seawater?
Its SALTY!!
Sea water contains about 3.5 dissolved solids
and 96.5 water
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These salts lower the freezing point of sea water
to -2C because the salt interferes with
lattice of ice crystals. (acts as antifreeze!)
This is why we can make ice cream!!
Adding salt to ice lowers the melting temperature
of the mix to -2C, but the water in the ice
cream mix still freezes at 0C. Thus, heat flows
from the mix to the salty ice.
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Oh, yeah, there are also some important consequenc
es for the ocean..
When sea water begins to freeze, the ice that
forms is pure water and the remaining liquid
is concentrated in salts. It is denser, and
this cold, salty water sinks into the deep ocean.
CREATESOCEAN CIRCULATION!
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The ocean acts as a thermal buffer it absorbs or
radiates heat in order to try to keep its
temperature constant
Sahara Desert (50C) to Antarctic continent
(-90C) on continents
140 C
Ocean changes from freezing (-2 C) to the
tropics (34 C)
36 C
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Why would Norfolk have a much larger temperature
variation than San Francisco?
(same solar input and both next to ocean)
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The ocean moderates the Earths surface
temperature by
1. transporting heat from the tropics where there
is an excess to the polar regions where there is
a deficit - currents such as the Gulf Stream
(1/3 from oceans, 2/3 from atmosphere)
2. Melting and freezing polar ice each year
(THINK which way does the heat flow in melting
and freezing)
3. Evaporation in tropical regions (and then
transport by atmosphere elsewhere)
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but not all of the ocean participates in this
buffering effect!
Cold, salty water is denser than warm, less
salty water.
What happens?
Dad, dense stuff SINKS!
.. and then, Bart, the cold, salty water rises
Why? GRAVITY!!!!
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The ocean is layered due to density
differences caused by
Sometimes salinity
Always temp.
Involved in buffering of climate
Surface zone - well mixed. WHY?
Waves, currents
Pyncocline - region of rapid increase in density
Deep zone - stable density, 80 of water
Isolated
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Movement between layers does not happen unless
density is about the same (WHY?)
Little solar heating!!
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Variations in sea surface temperature lead to
several climatic phenomena
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Salinity variations can be explained by a balance
between evaporation (makes water saltier) and
precipitation (makes water less salty)
PgtE
EgtP
PgtE
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What else happens in the surface, or mixed, zone?
LIFE!!
Life requires LIGHT - photosynthesis is the basis
of life for most of the planet.
but how deep does light go?
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Photic zone
Little light penetrates to below photic zone and
it is blue (hydrogen bonds in water absorb red
light)
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What you photo with a strobe
What you see
(only blue light)
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The effects of density, temperature, and salinity
layering affects provides places for submarines
to hide.
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Rule for refraction sound bends towards low
velocity
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