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Water – Physical Properties

Image: Brittany Ferries

H2O• Elemental building blocks

Atoms and Molecules

• A (not) – tomos (cut)– Fundamental building block of matter

• Molecule– Two or more atoms sharing electrons

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Water – H2O

• Polar molecule– Electrons are unevenly shared, giving

apparent negative and positive ends

Hydrogen Bonds

• Polarity of water results in weak attraction call hydrogen bonding. This is not a molecular bond! It does result in an ordered liquid with special properties.

Water’s Special Properties

• Cohesion and Surface Tension

• Capillarity

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Thermal Properties of Water

• As a gas water is unordered – energy is high enough to overcome hydrogen bonding

Thermal Properties of Water

• Order provided by hydrogen bonds provides more stability for liquid phase

Thermal Properties of Water

• Hexagonal crystals formed in solid phase actually cause ice to be less dense than liquid water

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Liquid Water’s Heat Capacity

• Water can remain a liquid despite the addition of more energy per unit mass

Heat = Energy

• Heat– Measured in calories (joules*)– 1 kilocalorie is 1000 calories– One calorie raises the temperature of water by 1

degree Celsius• Heat Capacity

– The quantity of heat needed to produce a unit change of temperature in a unit mass of material.

– The heat capacity of water is 1 calorie per gram

*1 calorie = 4.184 joules (J)

Phase Changes

• Heat of Fusion– Change fresh water from a solid at 0oC to a

liquid at 0oC requires 80 calories– This is the latent heat of fusion– There is no change in temperature only a

change in physical state– The heat is released again in changing liquid

water to ice.

Efus = 80 cal/g

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Phase Changes

• Heat of Evaporation– Change fresh water at 100oC to a vapor at

100oC requires 540 calories– This is the latent heat of evaporation– There is no change in temperature only a

change in physical state– The heat is released again in changing from

vapor to liquid water.

Evap = 565 cal/g

Phase Changes

Phase Changes in Water

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Evaporation and Precipitation

Salt and Phase Change• Adding salt (dissolved ions) into water

changes physical properties– Raises boiling temperature at a given

pressure– Lowers freezing temperature at a given

temperature

Salt and Phase Change

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Density

• Mass per unit volume– Liquid water at room temperature = 1 g/cm3

• Density effected by temperature, pressure, and salinity– Thermal contraction

• Expansion with heat• Contraction with lower temperatures

• But water is unusual…

Density of Water

• Density maximum at 4oC

• Ice less dense than liquid water– Ice floats!

USGS

Density of Seawater

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Formation of Sea Ice

Coolantarctica.com

Brine Rejection

• Water away from spheres of hydration freezes first

• Salinity in liquid increases

• Pockets of brine are left over and expelled to ocean

Sea Ice and Sea Level

• Does melting and freezing of sea ice affect global sea level?

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Pressure and Salinity

• Pressure– Increasing pressure increases density

• Water is not very compressible

• Salinity– Higher salinity increases density

• Cold salty waters are denser than warm fresher waters.

Transmission of Heat

• Conduction– This is a molecular process. When heat is

applied to one area, the molecules move faster and the energy spreads to adjacent ones.

• Convection– Convection is a density driven process

• Radiation– Direct transmission of energy by radiation

Temperature, Density, and Salinity Distributions

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Temperature, Density, and Salinity Distributions

Temperature, Density, and Salinity Profiles

Seasonal Thermocline Variations

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Seasonal Thermocline Variations

Halocline

• Rapid change in salinity with depth

Halocline

• Rapid change in salinity with depth

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Light Transmission through Water

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Light Transmission through Water

• Absorption• Scattering• Attenuation• By 10m, only 10% of light is

transmitted• By 100m, nearly no light is

being transmitted

Shallow Underwater

• Flash unable to cover large area

Shallow Underwater

• Close-up view allows flash to bring out reds and oranges

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Shallow Underwater

Natural light in backgroundCloser up, flash is more effective (less absorption)

Sound Transmission in Water

• Speed of sound in water is 5 times faster than in air

• Speed of sound increases with increasing pressure, temperature, and salt

Sofar Channel

• Sound Fixing and Ranging Channel

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Key Points

• Water Thermal Properties– Heats of fusion, evaporation, and heat content– Hydrogen bonding– Phase changes

• Light transmissivity• Sound transmissivity• Depth profiles – all of the ‘clines.