Water - Its Properties and Role in the Environment

Water - Its Properties and Role in the Environment

Outline: ? Role in early history and science ? Unique chemistry ? Hydrologic cycle - redistribution, climate effects ? Ocean circulation - basic wind & thermohaline

Chemically unique

Exists in all three phases at atmospheric temperatures & pressures (high melting and boiling points compared to molecules of similar size It is the only substance that does this!

Chemically and Physically unique

? High heat capacity (4.2 J/g/K). It stores a lot of heat energy which makes it a good medium for spreading the planet's heat

? High heat of fusion (solid to liquid ~ 335 J/g/K) and vaporization (liquid to gas ~ 2400 J/g/K) so more effectively transfers heat when changing phase in atmosphere/ocean

Physically Unique

?Water is physically unique because it is less dense as a solid (ice) than as a liquid. ?The maximum density of liquid water occurs at 4?C

Chemically and Biologically Unique

? High surface tension so it forms drops & helps make good cell membranes

? Dissolve other compounds very easily and so can transport chemicals (e.g., NaCl, nutrients)

? Mediates or facilitates most chemical reactions in living systems (e.g., takes water to photosynthesize) - neutral pH

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