The Sea Around Us
Lecture 3: Properties of Water:
The Wonder Substance
Today’s music:
Bill Nye Water Cycle Jump!
From: A Gentle Introduction to Water
www.chem1.com/acad/sci/aboutwater.html
NIGHTWISH - The Islander
Ron Pope - A drop in the ocean
The Presets - Girl and the sea
Thanks to Hannah P.,
Kara D. & Daisha M.
• Lecture Notes and
Review Questions
• TA Office Hours
(T 10-11 & W 2-3)
• On-line Assignment 1
is due tonight by 11pm
• Homework 1 due Jan
28
• Cell Phone Recycling
• Songs and Questions
(Angel)
World Ocean Council See link for Internship Program.
Florida couple planning for life under the sea
http://www.wtsp.com/news/s
cience/story.aspx?storyid=16
9031&catid=67
Current progress:
underseacolony.com/prime/mainhub_revA.html
Read your book anywhere and everywhere!
True (ocean) love!!?
Today is the first in-class iClicker
exercise for credit
A) Full credit if you answer 80% or more of
the questions
B) Bonus points if you get the correct
answer for 80% of more of the
questions
C) If there are 8 questions and you answer
at least 7 of them you’ll get full credit
(100%)
D) If there are 8 questions and you answer
at least 7 of them correctly you’ll get a
5% bonus (105%)
E) All of the above (this is the correct
answer, choose E!)
Water in the Oceans --and why we should be concerned
about the physical properties of water
•Importance to Physical & Biological Processes
•Water’s unique physical properties cause a buffering of
Earth’s surface and environmental changes, which
promotes continuity of life on Earth
•The physical properties of water determine how oceans
circulate, how heat is transferred by the ocean and
atmosphere, and the way waves work.
Water Promotes Continuity of Life on Earth
Low viscosity
•rapid flow to equalize pressure differences
Low compressibility
•Small change in volume for a change in pressure
High heat capacity
•cools/warms slowly relative to land
•aids in heat retention & transport
•minimizes extremes in temperature
•helps to maintain uniform body temps
High latent heat of evaporation/precipitation
•very important for heat transfer between ocean &
atmosphere (main source of energy for hurricanes!)
High surface tension
•allows wind energy to be transmitted to sea surface
•allows cells to hold shape --and life to form
•controls the behavior of water drops
Properties of Water: Surface Tension, Viscosity, Compressibility
Viscosity:
Is the resistance to shear motion
Increases as water cools
Is low for water, compared to say, ketchup
Low viscosity liquids pour or stir easily
Ketchup has high viscosity
Water has low
viscosity
Properties of Water: Surface Tension, Viscosity, Compressibility
Compressibility (can you squooosh it?) is:
• Very low for water
• The change in volume for a change in pressure
Think about:
In the ocean: pressure increases by 1 atm. (14.5 psi) for
every 10 m increase in depth
•at 4000 m, a liter of water (at the surface) is only ~ 2%
smaller
•Sea level would be 37m higher if water were totally
incompressible
before
After
Compression
Properties of Water: Surface Tension, Viscosity, Compressibility
Surface tension or capillary force (highest of all liquids)
•cohesion of liquid surface- intermolecular forces
•water forms weak "elastic" membrane
•increases as water cools
•decreases with increasing salt content
meniscus
Surface tension is what holds water drops together and
determines the shape of waves.
Ripples and small waves are generated by wind
energy and the surface tension of water.
Physical Properties of Water.
Check out Water Drop at 2000 Frames per Second
http://www.flixxy.com/water-drop.htm#.UPQpcIVe8oY%3Cp%3E
From Discovery Channel's series 'Time Warp' where MIT scientist and teacher Jeff
Lieberman and digital-imaging expert Matt Kearney use the latest in high-speed photography
to turn never-before-seen wonders into an experience of beauty and learning.
Physical Properties of Water: The Wonder Substance
Molecular Structure and Organization
•Bonding of hydrogens to oxygen
creates a "polar" molecule.
Water molecule:
• 105° angle
• unequal charge distribution: Polar
Molecular Structure and Organization:
Clustering of water molecules
What causes it?
•hydrogen bonds (weak interaction ~10%
of covalent strength)
•This property creates Surface Tension
Liquid water; bonds are constantly breaking and reforming
•each bond lasts a few trillionths of a second
•high proportion of molecules bonded at any instant
Water Promotes Continuity of Life on Earth
Low viscosity
•rapid flow to equalize pressure differences
High surface tension
•allows wind energy to be transmitted to sea surface
•allows cells to hold shape --and life to form
•controls the behavior of water drops
High heat capacity
•cools/warms slowly relative to land
•aids in heat retention & transport
•minimizes extremes in temperature
•helps to maintain uniform body temps
High latent heat of evaporation
•very important in heat/water transfer in atmosphere
Properties of Water
Unusual Properties--compare other liquids
Heat Capacity or Specific heat: What is it?
• Ability of a material to store heat
• Heat needed to change the temperature of a given mass of water
(1 gram or 1 kilogram) by 1 degree C
For Water:
heat capacity is: 1 cal per gram per deg. Celsius: 1cal/(gm °C)
• 1 calorie is the heat energy needed to raise 1 gm by 1°C
• 1 calorie ≈ 4.19 J (heat capacity of water is 4190 J/Kg °C)
• Need 41,900 J to raise the temperature of 1 kg (1 liter) of water
from 0 to 100° C
Heat capacity (high)
•only ammonia (NH3) higher
•H20 much higher heat capacity than rock or steel
3 phases of materials
Heat required to change
the temperature (by 1 deg.)
of a given mass
4190
J
Kg °C
-1
Temperature (°C)
Heat Capacity
Rock &
Soil
Liquid
water
Heat input (J/kg or cal/gram)
Heat capacity and phase changes:
ice (solid)
150
water (liquid)
vapor or steam (gas)
Vapor
100
vapor+ liquid
Liquid water
50
Latent Heat
Heat needed to
change phase (from
solid to liquid, liquid
to gas, liquid to solid,
etc.)
Latent heat of
vaporization or
condensation
540cal/gm
Ice + liquid
0
-50
Ice
Latent heat of
fusion or melting
80cal/gm
-100
0
200
400
600
Heat input (cal/gram)
800
Pepsi
Temperature (°C)
Heat Capacity
Heat required to change a given mass by a given temp.
J/kg or cal/gram
Lower Heat
Capacity
Higher
Heat
Capacity
Heat input (J/kg or cal/gram)
Latent Heat and Changes of State
Latent heat of fusion (or melting)
• Heat to form or melt ice (liquid to
solid phase)
• 333 kJ/kg (80 calories/gram)
Latent heat of vaporization (or precipitation)
• Heat to vaporize (boil) a liquid or condense
liquid from a gas phase
• 2260 kJ/kg (540 calories/gram)
Evaporation of water from the surface can occur at any
temperature. However, it takes more energy to evaporate at
low T than to boil off vapor once water reaches 100°C
The high heat capacity of water means that it
heats up and cools off more slowly than land.
Latent heat is a key factor in Hurricane
development and sustainability.
Properties of Water: Heat Capacity
What is heat capacity? Why is it so high for H20?
Adding heat to water:
• speeds up molecules
• break bonds
Hence, less warming or less evaporation than expected
When heat is removed from water:
• bonds form and restructure, material
condenses (e.g., gas to liquid)
• energy is released via bonds formation
Energy release causes heating and thus temperature
decrease is smaller than expected
Density of Water
•Fresh water reaches maximum density at 3.98 °C
•Density= 1,000 kg/m3 (1kg/liter)
• Density decreases
as water is heated
above 4°C
• At 20 °C, density
of pure H2O is
998.23 kg/m3
Density of Fresh Water & Ice
•Ice is less dense than water. Ice at 0 °C is 917.0 kg/m3
•Ice has an open hexagonal structure
Water molecular structure
Ice molecular structure
Density of ice is about
91% of liquid water
Water Promotes Continuity of Life on Earth
Low viscosity
•rapid flow to equalize pressure differences
High surface tension
•allows wind energy to be transmitted to sea surface
•allows cells to hold shape --and life to form
•controls the behavior of water drops
High heat capacity
•cools/warms slowly relative to land
•aids in heat retention & transport
•minimizes extremes in temperature
•helps to maintain uniform body temps
High latent heat of evaporation
•very important in heat/water transfer in atmosphere
• Heat is required to change
the phase of a substance (for
example, ice to water); this is
known as latent heat
50
water
0
• If we add heat to water (or
ice) the temperature rises,
this is known as sensible heat
Latent heat
Ice
Sensible
heat
-50
• Ice changes to water (melts!)
at 0° C
Temperature (°C)
Heat, Temperature and Changes of Phase
10
Heat
(cal, or Joules)
50
Heat required to change
the temperature (by 1 °)
of a given mass
Temperature (°C)
Heat Capacity
Rock &
Soil
30
20
Liquid
water
Pepsi
10
10
50
Heat input (J/kg or cal/gram)
Heat required to change
the temperature (by 1 °)
of a given mass
Temperature (°C)
Heat Capacity
Rock &
Soil
30
20
Liquid
water
10
10
50
Heat input (J/kg or cal/gram)
Heat required to change
the temperature (by 1 °)
of a given mass
Temperature (°C)
Heat Capacity
Rock &
Soil
30
20
Liquid
water
10
10
50
Heat input (J/kg or cal/gram)
Heat required to change
the temperature (by 1 °)
of a given mass
Temperature (°C)
Heat Capacity
Rock &
Soil
30
20
Liquid
water
10
10
50
Heat input (J/kg or cal/gram)
Heat required to change
the temperature (by 1 °)
of a given mass
Temperature (°C)
Heat Capacity
Rock &
Soil
30
20
Liquid
water
10
10
50
Heat input (J/kg or cal/gram)
Heat required to change
the temperature (by 1 °)
of a given mass
Temperature (°C)
Heat Capacity
Rock &
Soil
30
20
Liquid
water
10
10
50
Heat input (J/kg or cal/gram)
Heat capacity and phase changes:
ice (solid)
150
water (liquid)
vapor or steam (gas)
Vapor
100
vapor+ liquid
Liquid water
50
Latent Heat
Heat needed to
change phase (from
solid to liquid, liquid
to gas, liquid to solid,
etc.)
Latent heat of
vaporization or
condensation
540cal/gm
Ice + liquid
0
-50
Ice
Latent heat of
fusion or melting
80cal/gm
-100
0
200
400
600
Heat input (cal/gram)
800
Density of Water
•Fresh water reaches maximum density at 3.98 °C
•Density= 1,000 kg/m3 (1kg/liter)
• Density decreases
as water is heated
above 4°C
• At 20 °C, density of
pure H2O is 998.23
kg/m3