The Sea Around UsLecture 3: Properties of Water: The Wonder Substance

Today’s music:

Dave Matthews Band“Don’t Drink the Water”

Bill Nye the Science Guy

Water Cycle Jump!

The Who“Water”

From: A Gentle Introduction to Waterwww.chem1.com/acad/sci/aboutwater.html

• Lecture Review Questions:

• TA Office Hours (T & W 11-12)

• On-line Assignment 1 is due tonight by 11pm

• Homework 1 will be posted soon

• Cell Phone Recycling

• Book pics! (Angel dropbox)

Thanks to ESMARLIN R.Read Chap. 5 of Trujillo and Thurman(on reserve in EMS Library, Deike Bld)

Climate secrets of Mariana Trench probed (BBC news)

The international team used a submersible, designed to withstand immense pressures, to study the bottom of the 10.9km-deep “underwater canyon.” Their early results reveal that ocean trenches are acting as carbon sinks. This suggests that they play a larger role in regulating the Earth's chemistry and climate than was thought.

http://www.bbc.co.uk/news/science-environment-12183244

Fish eating at 7.7km depth

Oceans in the News17/01/11

Where Did the Oceans Come From?

Empirical vs Belief-Based Approaches

• Truth is based on authority (of texts, self-proclaimed or selected leaders, legends, etc.) and is generally inviolable.

• Truth is based on application of a standardized method and repeated tests to confirm a result, and is subject to change as new methods are developed and new results discovered.

In other words, theories evolve…

Belief-based vs. empirical approaches to knowledge

The Source Of Authority?

Belief system

Definitions are simply decrees. They are not based on Science

The Theory of Evolution is Based on The Scientific Method

A theory based on scientific principles and

rigorously tested by skeptical

scientists for over a century and a half!

15% of your grade is based on in Class Exercises (using clickers)

Marone’s Theory of Grades

Empirical* system:

MeasurementsObservationsHypotheses

Theories

Scientific MethodParameter “X”

Par

amet

er “

Y”

“Correlations”

*empirical means “experiential” or “searching for interrelationships”

Scientific method: definitionsFACT : observation repeatedly confirmed

HYPOTHESIS: testable statement about the natural world (a working model)

THEORY: a set of verified hypotheses that explain how things work. A theory explains most or perhaps all of the observations, but ‘the jury is still out,’ for one reason or another.

LAW: generalization of how some aspect of natural

world behaves under stated circumstances;

repeatedly-verified explanation of some aspect of the natural world

1. Initial observation of materials/phenomena/behavior

2. Development of

questions/establishment of

constraints

3. Formulation of models to explain

behavior: MULTIPLE WORKING HYPOTHESES

4. Testing of hypotheses through

observation/experiment;

COLLECTION OF DATA

(MEASUREMENTS)

5. Analysis of data,

evaluation/interpretation of results

(ELIMINATE HYPOTHESES)6. Formulate conclusions.

THE SCIENTIFIC METHOD

Scientific Method Hypotheses and Theories must be falsifiable.

That is, we can never “prove” an hypothesis, we can only disprove it

We must accept some uncertainty until substantial observations and tests have been conducted.

Some problems do not yield easily and answers are complex (for example--the origin of water on Earth; the carbon cycle; global climate, earthquake prediction

The Habitable Zone

Where did Earth’s Water Come From? And Why is it

Still Here?

Seawater Origin and Evolution

Earth: The Third Stone from the Sun (Jimi is not dead!)• The chemical evolution of Earth’s ocean and

atmosphere is intimately related to the processes that formed the Earth--the water planet.

• Why does Earth have liquid water whereas the other planets do not at present? Or do they?

Where’s Pluto?

Seawater Origin and Evolution

Is it a planet ?!

The chemical evolution of Earth’s ocean and atmosphere is intimately related to the processes that formed the Earth--the water planet. Why does Earth have liquid water whereas the other planets do not at present? Or do they?

The “Goldilocks Principle”

Planetary mass

High gravity retainslight volatile gases =thick atmosphere

Low gravity losesall atmospheric

gases

Boiling breakschem bonds

Freezing stopsall biochem rxns

0°

100°

LIFE ZONE

solid

liqui

dg

as

SURFACETEMPERATURE

Distance from sun

The “Goldilocks Principle”

*(°C

)

ATMOSPHERICCOMPOSITION

INTERNAL COMPOSITION

http://www3.geosc.psu.edu/geosc040/40.lecture_files/

NASA “Global Surveyor” mission map of ancient oceans on Mars (orbiter, 1997)

WATER on MARS 4 BILLION YEARS AGO?

Photos and mosaic JPL/ NASA

The Grand Canyon of Mars - Valles Marineris

3000 km

Water-formed gullies in crater

Summary: Origin of Water on Earth and in the Oceans

Two Major HypothesesEarth Belch –degassing of volatile chemical species (water, C02, etc. Substances easily driven off by heatVolcanic Eruptions, Hot Springs, Seafloor Vents

E.T ? Comets and meteorites. Impacts big and small

Chat with at least 3 people around you. See if you could get together with them to go over course materials and study for exams in this course.

Does the person on your right live

A) On campus

B) Off campus

This image shows the distribution of Earth’s surface water. Which is/are correct?

A) Most of Earth’s surface water is in the Ocean

B) Rivers and Lakes account for more water than the Atlantic Ocean

C) Land ice (glaciers) account for most of the surface water that’s not in the ocean

D) A and C

E) Rain and clouds contain as much water as the ocean

Water in the world ocean came from Earth’s interior

A) This is a falsifiable, scientific hypothesis

B) This is a known, proven fact

C) This is reasonable, based on what we know about Earth’s composition and internal structure

D) All of the above

E) A and C

Ocean water most likely formed:

a) During the first 0.5 x 109 years of Earth’s history

b) Largely from emission (degassing) of materials (volatiles) from Earth’s interior

c) From melting of glaciers and polar ice caps

d) (a) and (c)

e) (a) and (b)

So, How Would You Answer This Question?

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

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/precipitation• very important for heat transfer between ocean &

atmosphere (main source of energy for hurricanes!)

Properties of Water: Surface Tension, Viscosity, Compressibility

Viscosity:Is the resistance to shear motion Increases as water coolsIs low for water, compared to say, ketchupLow viscosity liquids pour or stir easily

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

After Compressio

nbefore

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.

http://www.flixxy.com/water-drop.htm#.UPQpcIVe8oY%3Cp%3E

Physical Properties of Water.Check out Water Drop at 2000 Frames per Second

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 EarthLow viscosity

• rapid flow to equalize pressure differencesHigh 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 WaterUnusual Properties--compare other liquids

Heat capacity (high)• only ammonia (NH3) higher• H20 much higher heat capacity than rock or steel

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 = 4190 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

3 phases of materials

Heat input

Tem

pera

ture

(°C

)

water

Heat, Temperature and Changes of PhaseWhich statement is correct about this plot?

A. Ice changes to water at 50° C

B. Heat is required to change ice to water and this is known as latent heat

C. Once the ice melts, heat will cause temperature to rise, this is known as sensible heat

D. B & C

E. None of the above

Ice

05

0-5

0

Heat Capacity Heat required to change the temperature (by 1 °) of a given mass

Heat input (J/kg or cal/gram)

Tem

pera

ture

(°C

)

Liquid water

Rock & Soil

4190Kg °C

J-1

Heat capacity and phase changes: ice (solid)

water (liquid) vapor or steam (gas)

0 200 400 600 800Heat input (cal/gram)

Tem

pera

ture

(°C

)

150

100

-100

50

0

-50

Liquid water

Ice

Vapor

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

Latent heat of fusion or melting 80cal/gm

Ice + liquid

vapor+ liquid

Clicker question:

Which is the best answer

A. Viscosity is a measure of resistance to shear motion

B. A low viscosity liquid pours more slowly than a high viscosity liquid

C. The viscosity of water is zero

D. Water is highly compressible, which means that 1 kg of it occupies a much, much smaller volume at the bottom of the ocean than near the ocean surface

E. A & D

Consider: two identical pots, filled with equal masses of fluid, on identical burners on a stove.Pot A is filled with a fluid of low heat capacityPot B is filled with a fluid of high heat capacity

After a time…..

A. The material in Pot A has reached higher temp.

B. The material in Pot B has reached higher temp.

C. Both pots are at the same temp.

Heat Capacity is the heat required to change the temperature (by 1 °) of a given mass of material

Heat input (J/kg or cal/gram)

Tem

pera

ture

(°C

)

Higher Heat Capacity

Lower Heat Capacity

Heat Capacity Heat required to change a given mass by a given temp.

J/kg or cal/gram

Pepsi

Heat Capacity Heat required to change a given mass by a given temp.

J/kg or cal/gram

Heat input (J/kg or cal/gram)

Tem

pera

ture

(°C

)

Higher Heat Capacity

Lower Heat Capacity

It’s game day, and you want to keep your Pepsi cold as long as possible.

You should fill your cooler with:

A. A material with high heat capacity

B. A material with low heat capacity

C. Doesn’t matter because you’re trying to keep it cold, not hot

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 CapacityWhat 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 formationEnergy 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