Physical properties of seawater
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PHYSICAL PROPERTIES OF SEAWATER. How Unique is Water?. Water is one of only 3 naturally occurring liquids (mercury and ammonia) Only substance occurring naturally that exists in all 3 states – solid , liquid, and gas – on Earth’s surface Extremely large liquid range (0 o C - 100 o C)

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How unique is water
How Unique is Water?

  • Water is one of only 3 naturally occurring liquids (mercury and ammonia)

  • Only substance occurring naturally that exists in all 3 states – solid, liquid, and gas – on Earth’s surface

  • Extremely large liquid range (0oC - 100oC)

  • Expands, becomes less dense as a solid

The nature of pure water
The Nature of Pure Water

  • Water made of 2 hydrogen atoms and 1 oxygen atom

  • Water is a polar molecule (+ end & – end)

  • Water’s unusual structure causes them to “stick together”

  • Water molecules form hydrogen bonds

  • Hydrogen bonds not very strong, but make water different from any other substance on Earth

Water has
Water has…

  • Cohesion – sticks to itself

  • Adhesion – sticks to others

  • Surface Tension – a measure of how difficult it is to stretch or break the surface of water

    • No waves without surface tension

Water has1
Water has…

  • Low Viscosity – little resistance to flow

  • Good for Earth’s marine organisms – WHY?

The three states of water
The Three States of Water

  • Water is the only substance that naturally occurs as a solid, liquid and gas on Earth

    • Evaporation absorbs heat

    • Condensation releases heat

Water is weird
Water is Weird

  • Density – the mass of a certain volume of a substance

  • Solid water is less dense than liquid water

  • Water becomes more dense as it cools

    • Water is most dense @ 4º C

    • Becomes less dense as it nears 0º C

  • Good for the planet – WHY?

Heat capacity
Heat Capacity

  • The amount of heat required to raise the temperature of 1 gram of a substance 1º C

    • Water has one of the highest

    • 1 calorie raises 1 gram of water 1º C

    • It absorbs large amounts of energy before the temperature changes

  • Good for earth’s climate – WHY?

Changes of state
Changes of State

  • Latent Heat of Fusion / Melting –

    • The amount of heat required to melt a substance without change in temperature

    • 80 calories per gram

Changes of state1
Changes of State

  • Latent Heat of Vaporization / Evaporation–

    • The amount of heat required to change a substance from a liquid to a gas without change in temperature

    • 540 calories per gram

Why is water important
Why is Water Important?

  • Water is the universal solvent

  • Water can dissolve more than any other natural substance

  • Water can dissolve many hydrophilic substances

    • Ionic compounds

    • Other polar compounds

  • Form “spheres of hydration”


Seawater has dissolved solids
Seawater has dissolved solids…

  • Source –

    • Chemical weathering of crustal rocks

    • Hydrothermal vents

    • From volcanic eruptions


  • Density of pure water is 1 g/mL @ 4º C

  • Density of seawater is 1.0278g/mL @ 4ºC

  • Density is determined by temperature and salinity

    • Seawater gets denser as it gets saltier, colder or both

  • Because temperature varies more than salinity, density is controlled by temperature


  • Changes with depth

  • Densest water sinks

  • Ocean becomes layered, stratified

  • Seen in profiles of salinity, temperature, and density

  • The greater the difference in density between surface and deep water, the more stable the water column and the harder it is to mix vertically


  • Water is noncompressible– does not change volume with increasing pressure

  • So is seawater

  • Pressure increases with increasing depth

    • Has small effect on volume

    • 1 atm (14.7 lbs/in2) for every 10 m (33 ft)

    • Pressure in deepest trench ~1100 atm

    • As pressure increases, gases are compressed


  • The ability of an object to float by displacing a volume of water equal to its own weight


  • Transmits energy

    • Heat

    • Light

    • Sound

  • Refraction – the bending of light and sound waves due to density differences that affect the speed of energy transmission

    • increases with increasing salt, decreases with increasing temperature


  • Transmits heat energy by

    • Conduction – molecule to molecule

    • Convection – moving fluids & density driven

    • Radiation – direct from source (sun)

Water is
Water is …

  • Transparent – transmits light energy readily

    • Important for photosynthesis

    • Oceans are blue because blue light penetrates the deepest

    • Coastal waters sometimes green because blue absorbed


  • Transmits soundfaster & farther than in air

    • 1500 m/s in seawater (& 60 times farther)

    • 334 m/s in air

  • At 1000 m combination of salinity, temp & pressure creates a zone of minimum velocity for sound – the Sofar Layer (sound fixing and ranging layer)

    • Sound waves produced here do not escape & travel long distances