Oceans are filled with??? The Water Molecule. Hydrogen Bonding between Polar Molecules: WATER!!!!! Let s understand water then.

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1 Oceans are filled with??? WATER!!!!! Let s understand water then. The Water Molecule V -shaped molecule: 105º angle between H nuclei Due to covalent bonds involving Oxygen s p-orbitals P-orbitals are 90º apart, but the hydrogen nuclei repel each other (Born repulsion) resulting in 105º between hydrogen nuclei Polar molecule: Electronegativity of Oxygen pulls electrons away from Hydrogen nuclei Electron cloud around Oxygen results in negative charge at the Oxygen side and positive charge at the Hydrogen side of the molecule Polar property leads to hydrogen bonding Hydrogen Bonding between Polar Molecules: Hydrogen bonds positive H ends attract negative O ends Water molecules thus stick together The polar water molecule and resulting hydrogen bonds are responsible for ALL water s REMARKABLE properties! E.g. Surface Tension Highest among common liquids Makes drops! Other strange properties resulting from Hydrogen Bonds, large heat capacity, large latent heats of fusion and vaporization, Strange Density variations 1

2 Freezing & Density: Ice floats! Freezing = removal of heat, Slows vibrations (lowers Temperature) Structure becomes compact - increase density Read pp Max density 1g/cc at 4ºC Below 4ºC rigid framework develops (0.99g/cc 0ºC) Ice - expanded structure: 105º to 109º 0.92 g/cc at 0ºC Phases of Water: Boiling point and freezing point are in normal range of temperature! Thus, water is present nearly everywhere No other substance is present in all phases on Earth s surface! Phase Changes - change P and T (condensation, sublimation, boiling) Heat & Phase Changes: The Calorie is the unit of measure of Heat Definition of a Calorie: Heat required to raise 1 gram of H 2 O by 1ºC The more water you have, the more heat required! Temperature is not heat! Heat = Energy. This energy causes molecules to vibrate (number of molecules & how fast) Temp = how fast are molecules vibrating (does not account for number of molecules). 2

3 Which contains more heat? A. Candle flame B. Warm Bath Heat Capacity = amount of heat required to raise Temperature of a substance 1ºC (this is a definition!) Heat Capacity of Water = 1 calorie/mole/ºc (definition of calorie) Highest of all common solids & liquids! Note to science majors: the heat capacity per gram of substance is the Specific Heat Hydrogen bonds in water are the cause of this LARGE heat capacity need lots of heat energy to vibrate all those hydrogen bonds and raise temperature! Heat Capacity of water > most solids (20 x that of quartz) Few liquids have greater Heath Capacity - e.g. ammonia Examples: water vs. ethyl alcohol Ethyl alcohol s Heat Capacity = 1/3 calorie Quartz sand (beach) vs. water Heat Capacity of quartz = 0.2 cal Big Point about Heat Capacity: Water has very high Heat Capacity - RESISTS changes in Temperature while absorbing or releasing heat. Compared to continents, Oceans require more heat to change temperature! Therefore, no wide diurnal or seasonal variations in ocean temperature. THUS vast amounts of Heat are moved around the globe as oceans circulate! Which is to say Water can store & transport lots of heat! Or Water controls heat budget of Oceans- Atmosphere-Crust! 3

4 Review: What is Heat Capacity A. A Measure of Energy B. The capacity of a substance to radiate heat C. The amount of heat needed to change temperature Review: High heat capacity allows. A. Water to transport great quantities of heat B. Water to store great quantities of heat C. Oceans to regulate climate D. All of the above Which way does heat flow? A. The baby will boil B. The candle will cool C. Cannot know 4

5 Heat flow and how oceans regulate climate: Clausius taught us that heat flows down a temperature gradient Analogy: balls roll down hill under force of gravity Heat flows from hot to cold under the force of entropy (dq = T/dS) Oceans have high heat capacity compared to continents Thus, no great change in temperature of oceans relative to the continents During winter, oceans are warmer than continents and heat is transferred to the continents During summer, oceans are cooler than continents and heat is transferred to the oceans Continental temperature difference ~ 140ºC N.Africa ~50ºC, Antarctic ~-90ºC Oceanic temperature difference ~ 34ºC Tropics ~ 34ºC, Arctic ~-2ºC This is the lake Effect or the Thermostatic Effect Sun s heat warms oceans unevenly - warm tropics, cool high latitudes Causes convection currents How much heat is transferred (by convection!)? How does water transfer heat? See discussion of Latent Heat What happens in a phase change? Melting ice: Ice has long-range order = crystal Add E, vibrate structure and disrupt order = melting to water Water has v. short-range order = liquid Boil water: Add E, vibrate hydrogen bonds and disrupt order, super energetic molecules escape to vapor Vapor has no order - individual molecules Latent Heat & Phase Changes: Cartoon What is Latent Heat? E required to melt or boil Consider icy cool lemonade Initially 0ºC, as ice melts what is the Temp? Latent heat fusion = Heat consumed during melting ice to water (80 cal/g ice) 5

6 Latent Heat of Fusion = 80 cal/g Latent Heat of Fusion is quite large Heat required to melt ice Also, Heat liberated during freezing! Highest among all common solids/liquids! Latent Heat of Vaporization = 540 cal/g Latent Heat Vaporization is HUGE Heat require to turn liquid at 100ºC into vapor Latent Heat Evaporation = 585 cal/g Heat require to turn liquid < 100ºC into vapor Zeer Pot Liberated molecule must take heat energy from surrounding Nigerian water molecules - thus the cooling effect of evaporation. invention uses Heat liberated during condensation LHV to Highest of all common substances - VERY IMPORTANT to refrigerate ocean/atmosphere food When water condenses in the atmosphere to form rain or clouds.. A. Heat is transferred to the atmosphere. B. Heat is transferred to the water, which falls back to the oceans. C. Heat is transferred to the continents, warming them and making high latitudes habitable. 6

7 Thermostatic effects of water s latent heat Evaporation - condensation on global scale cools oceans and warms the atmosphere at low latitude evaporation removes heat from ocean (cools tropical seas) At high latitude condensation releases heat to to the atmosphere (warming)! Heat stored/released by sea ice: Annual volume change: 18,000 km 3 How much Heat? ~1.44 x10 21 calories absorbed during melting! ~1.44 x10 21 calories liberated during freezing! Heat transported by Gulf Stream Gulf Stream outflow 10ºC warmer than return flow. Flow is 55 x 10 6 m 3 per second Calculate 550 trillion calories per second! ~550 x 10 9 calories transferred to atmosphere Atmospheric transfer is even greater! 7

8 Convection in the Oceans- Cooling of surface water at high latitude Warming of surface water at low latitude North Atlantic Cooling Equator Heating We will return to this Review Questions What single feature of water is responsible for some of its important properties (e.g., high heat capacity)? Which direction does heat flow during melting of ice, crystallization of ice, evaporation of water and condensation of water? How do the oceans influence climate? 8