Properties Of Water And Sea Water Class 14 -- The Oceans Properties Of Water And Sea Water Why is water such an unusual substance? Structure of the H2O molecule States of H2O, and energy transfer in changes of state Density, and effects of temperature Sea water -- the effect of dissolved salts

The Water Planet

The Most Important Driver of Earth Surface Processes WATER (H2O): The Most Important Driver of Earth Surface Processes Most common substance at the surface Less common on the surface of other planets Essential for life Unusual properties Excellent solvent for ions Absorbs (and releases) large amounts of energy Regulates climate

The Water Planet

STRUCTURE OF H2O MOLECULES Non-linear --> electrically "polar" + and - charged ends "H-bonding" = attraction, + and - Unusual properties result from this Strong solvent for ions Charges attracted by charged ends of the water molecules

STATES (PHASES) OF H2O Ice -- All H2O’s are H-bonded in an orderly crystal structure Liquid Water -- H2O’s about as close as in Ice, BUT not rigidly held free to move somewhat Vapor -- Free molecules, far apart

Energy Absorbed Or Released In H2O Phase Changes Ice <--> Water -- 80 calories/gram Water <--> Vapor -- nearly 600 cal./gram Large amount!

Why so much energy? Evaporation --> energy required to break H-bonds Condensation --> energy liberated when H-bonds form So... Water is an efficient means of moving heat energy around (as you well know!!!)

Water vapor = “latent” heat

Heat on the earth- Huge role for water vapor Evap. of sea water --> water vapor in air Cools the ocean Heat energy transferred to water vapor Water vapor moved to higher latitude Condensation of water vapor: WARMS the atmosphere; main way heat is transported from low to high Latitude

Water vapor = “latent” heat

HEAT CAPACITY (= specific heat) How much energy is needed to heat up a substance...OR How efficiently heat is stored in a substance Definition: "Energy required to raise the temperature of one gram of the substance by 1˚C.”

WATER HAS A LARGE HEAT CAPACITY 1 calorie / g - ˚C ... very high! Rocks and soils = 0.2 cal. / g - ˚C. Consequences of this difference... Oceans and lakes gain/lose much heat with little T change (moderates T) Land heats and cools much more easily

Warmer = less dense, right? Density Warmer = less dense, right?

DENSITY Mass per unit volume, e.g., grams/cm3 Pure water (at 4˚C) = 1.000 g/cm3 Ice = 0.92 g/cm3 . . . Less than liquid ...unusual! Sea water = 1.021 - 1.028 g/cm3 Large water bodies tend to be stratified (= layered) Top layers -- least dense Bottom layers -- most dense